Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

Influence of the Rhizobacterium Rhodobacter sphaeroides KE149 and Biochar on Waterlogging Stress Tolerance in Glycine max L.

Influence of the Rhizobacterium Rhodobacter sphaeroides KE149 and Biochar on Waterlogging Stress... environments Article Influence of the Rhizobacterium Rhodobacter sphaeroides KE149 and Biochar on Waterlogging Stress Tolerance in Glycine max L. Sang-Mo Kang, Arjun Adhikari , Muhammad Aaqil Khan , Eun-Hae Kwon, Yong-Sung Park and In-Jung Lee * Department of Applied Biosciences, Kyungpook National University, 80 Daehakro, Bukgu, Daegu 41566, Korea; kmoya@hanmail.net (S.-M.K.); farmerarjun7@gmail.com (A.A.); aqil_bacha@yahoo.com (M.A.K.); eunhaekwon@naver.com (E.-H.K.); Pjyjsj3@gmail.com (Y.-S.P.) * Correspondence: ijlee@knu.ac.kr; Tel.: +82-53-950-5708 Abstract: In the context of the current climate change and increasing population scenarios, wa- terlogging stress in plants represents a global threat to sustainable agriculture production. Plant- growth-promoting rhizobacteria and biochar have been widely reported to mitigate the effects of several abiotic stresses. Hence, in the present study, we examined the effect of the rhizobacterium Rhodobacter sphaeroides KE149 and biochar on soybean plants subjected to sufficient water supply and waterlogging stress conditions. Our results revealed that KE149 and biochar inoculation significantly improved plant morphological attributes, such as root length, shoot length, and fresh biomass. The biochemical analysis results showed that the two treatments determined a significant drop in the levels of endogenous phytohormones (such as abscisic acid) under normal conditions, which were considerably enhanced under waterlogging stress. However, the jasmonic acid content increased with Citation: Kang, S.-M.; Adhikari, A.; the application of biochar and KE149 under normal conditions, and it considerably decreased under Khan, M.A.; Kwon, E.-H.; Park, Y.-S.; waterlogging stress. Moreover, proline, methionine, and aspartic acid were significantly increased, Lee, I.-J. Influence of the whereas the phenolic and flavonoid contents were reduced with the application of the two treatments Rhizobacterium Rhodobacter under waterlogging stress. These results suggest that the application of KE149 and biochar can be sphaeroides KE149 and Biochar on a safe biological tool with which to improve the physiology and productivity of soybean plants Waterlogging Stress Tolerance in exposed to waterlogging stress. Glycine max L. Environments 2021, 8, 94. https://doi.org/10.3390/ environments8090094 Keywords: biochar; soybean; Rhodobacter sphaeroides KE149; waterlogging; abiotic stress Academic Editor: Wen-tien Tsai Received: 6 August 2021 1. Introduction Accepted: 13 September 2021 Exposure to abiotic stress is one of the major causes of low productivity of agricul- Published: 15 September 2021 tural crops, and [1] waterlogging stress, in particular, is prevalent globally in agriculture sites [2]. Climate change, influenced by massive anthropogenic human activities, has Publisher’s Note: MDPI stays neutral further triggered water stress in lands used for agricultural production. In general, water with regard to jurisdictional claims in stress is categorized as (i) water deficiency and (ii) excess water exposure, which includes published maps and institutional affil- waterlogging and complete submergence [3]. Plants face several physiological abnormal- iations. ities when subjected to water stress. The main processes induced are the generation of reactive oxygen species (ROS) in cells, ionic imbalance, electrolytic leakage, and osmotic stress, which all ultimately result in cell death. To counteract these stress reactions, the plant undergoes several functional changes that include molecule signaling, antioxidant Copyright: © 2021 by the authors. production, phytohormone modulation, and amino acid biosynthesis [3–5]. Licensee MDPI, Basel, Switzerland. Phytohormones such as abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) This article is an open access article are widely reported as being associated with stress tolerance [6]. ABA plays a key role in distributed under the terms and the regulation of stomata to confer water stress resistance [7,8], SA is a natural phenolic conditions of the Creative Commons compound that activates the defense system against pathogens and abiotic stresses [9], and Attribution (CC BY) license (https:// JA induces defense mechanisms, in addition to activating antioxidants and participating in creativecommons.org/licenses/by/ amino acid accumulation and cross-signaling [10]. 4.0/). Environments 2021, 8, 94. https://doi.org/10.3390/environments8090094 https://www.mdpi.com/journal/environments Environments 2021, 8, 94 2 of 13 Antioxidants play a key role in minimizing the detrimental effects of oxygen radi- cals generated in plant cells in response to abiotic stress [11]. Among the antioxidants, flavonoids are known to improve yield quality, while phenolic compounds are known to scavenge ions to neutralize ROS [12]. Similarly, the amino-acid-like proline, methionine, and aspartic acid are actively involved in metal sequestration, radical scavengers, stabi- lizers of macromolecules, electron sinks, and manufacturing cell wall components [13]. Therefore, it is vital to improve plants’ physiological aspects under stress in order to achieve optimal crop production. Plant-growth-promoting rhizobacteria (PGPR) and biochar are emerging biostimulants that have been reported to improve metabolism and confer tolerance in crops subjected to several biotic and abiotic stresses [14,15]. Biochar and PGPR are biologically safe tools, and they work symbiotically to improve plant metabolism. The functional aspects of PGPR include the production of secondary metabolites, ion regulation, the improvement of ion absorption through roots, and translocation to shoots [16,17]. Similarly, biochar replenishes the soil, enhances carbon sequestration, and facilitates microbial growth [18,19]. Numerous studies have reported the beneficial role of PGPR application for plant growth and development [20]. In addition, Abideen et al. [18] showed that biochar application improved the growth of Phragmites karka under water stress conditions, and Kammann et al. [21] reported that appropriate doses of biochar improved the growth of Chenopodium quinoa, also subjected to water stress. Moreover, PGPR and biochar are widely known to improve the growth of several leguminous crops [22,23]. Leguminous plants are highly prone to waterlogging stress [24,25]. The photosynthetic activity of Rhodobacter spp. has been widely reported to mitigate stress in plants [26–28], and biochar is recognized as a stress reliever and growth promoter [29]. Considering these facts, the aim of the present study is to understand the metabolomic perspectives of soybean plants treated with biochar and the plant-growth-promoting bacterium Rhodobac- ter sphaeroides KE149, during exposure to waterlogging stress. The tested hypothesis is that PGPR and biochar have a potential role in regulating ion absorption through roots, regulating phytohormones, and amino acid synthesis in soybean plants exposed to waterlogging stress. 2. Materials and Methods 2.1. Selection of Microbes The bacterium Rhodobacter sphaeroides KE149 was selected for the current experiment based on the results obtained from our previous study, where KE149 was reported to have various plant-growth-promoting traits, including the ability to confer resistance against water stress in adzuki bean plants [30]. 2.2. Experiment Location, Method, and Design The experiment was conducted at the greenhouse of Kyungpook National University, Daegu, Korea, located at longitude 128.587655 E and latitude 35.857655 N. Soybean (Glycine max L. cv. Taekwang) seeds were surface-sterilized with 1% Tween solution and 2% perchloric acid, and were washed thoroughly with sterile distilled water. The seeds were then sown into pots filled with autoclaved soil containing peat moss (13–18%), perlite (7–11%), coco-peat (63–68%), and zeolite (6–8%), with the following macro-nutrients: NH ~90 mg/kg, NO ~205 mg/kg, P O ~350 mg/kg, and K O~100 mg/kg. Three- 4 3 2 5 2 week-old soybean plants (50 per treatment) were treated with 10 mL of bacterial culture 8 –1 (10 CFUmL ) and oak wood biochar (0.1% per pot). The biochar consisted of dolomite 10%, zeolite 5%, molasses 10%, peat 5%, and diameter 3–4 mm. Seven days later, soybean plants, with and without bacterial treatment, were subjected to waterlogging stress. The pots were kept in a tray and water was applied on daily basis to maintain the water level up to 5 cm above the soil surface. The experiment was designed as no stress (NS) and waterlogging stress (WLS). The length and fresh weight of shoots and roots in addition Environments 2021, 8, 94 3 of 13 to chlorophyll content were measured after 7 days of waterlogging treatment, and plant samples were collected for further biochemical analyses. 2.3. Measurement of Realtive Water Content and Chlorophyll Content The relative water content (RWC) was measured according to the method described by Wattoo [31]. The chlorophyll content was measured by using a CCM-300 chlorophyll content meter (Opti-Sciences, Hudson, NH). This instrument uses a fiber optic probe that detects the emission rate of red to far-red fluorescence (700 nm to 735 nm) [30]. 2.4. Quantification of Endogenous Phytohormones ABA: The method described by Bhusal et al. [32] was used to quantify the ABA content in plant shoots. In brief, one gram of freeze-dried sample was extracted with isopropanol and acetic acid (95:5 v/v). The obtained solution was filtered and an internal standard [()-3,5,5,7,7,7-d6)-ABA] was added. The extract was washed with 1 N NaOH and chlorophyll was separated by CH CL . Subsequently, polyvinylpolypyrrolidone was 2 2 added and the solution was stirred for an hour; then it was filtered, evaporated, and finally extracted through ethyl acetate/diethyl ether. The ABA extracts were analyzed by GC-MS/SIM (6890 N Network GC System and 5973 Network Mass Selective Detector; Agilent Technologies, Santa Clara, CA, USA). JA: The protocol described in Adhikari et al. [33] was used to obtain the JA extract. In brief, one gram of freeze-dried ground sample was extracted using acetone/citric acid (70:30 v/v) and filtered. The (9,10– H )-9,10- Dihydro-JA (100 ng) was added as an internal standard. Methylation was performed using diethyl ether followed by dichloromethane. The peaks were obtained using GC-MS/SIM technology (6890 N Network GC System and 5973 Network Mass Selective Detector; Agilent Technologies, Santa Clara, CA, USA). SA: SA was quantified based on the method used by Adhikari et al. [34]. In brief, 0.5 g of lyophilized sample was extracted with 100% methanol, was centrifuged, and the solution obtained was vacuum-dried and suspended in trichloroacetic acid (5%). The solution was then partitioned by cyclopentane, ethyl acetate, and isopropanol, and subsequently it was dried using N . The excitation and emission peaks at 305 nm and 355 nm were recorded respectively using HPLC (Shimadzu RF-10AXL fluorescence detector). 2.5. Amino Acid and Antioxidant Analyses The method described by Shahzad et al. [35] was used to quantify the amino acid content in soybean shoots. In brief, 0.05 g of lyophilized sample was suspended with 6 N HCl and charged with N . The sample was kept airtight at 110 C on a hot plate for 24 h and was dried at 80 C for the next 24 h. The extract was obtained with 0.02 N hydrochloric acid and injected into an amino acid auto-analyzer (Hitachi, Japan). For the analysis of antioxidants, phenolic and flavonoid contents were measured based on the methods described by Adhikari et al. [36] and Adhikari et al. [37], respectively. 2.6. Statistical Analysis The present study was conducted using a completely randomized design with six replicates for each treatment. The data were analyzed in SAS 9.4 (SAS Institute, Cary, NC, USA) and evaluated using Duncan’s multiple range test (DMRT) at p  0.05. 3. Results 3.1. Effect on Morphological Attributes and Relative Water Content The inoculation of KE149 and biochar in soybean improved morphological character- istics such as root and shoot length as well as total biomass. Under normal conditions, the plants treated with KE149 and biochar showed a 52% and 58% increase, respectively, in shoot weight. A similar trend was observed under waterlogging conditions, where the shoot weight increased by 26% and 29%, respectively in the two treatments. Minor differ- ences were observed in shoot and root lengths under normal conditions. However, under Environments 2021, 8, 94 4 of 13 waterlogging conditions, shoot length increased by 15% and 25% in the two treatments, respectively, and root length increased by 26% and 27%, also respectively (Table 1 and Figure 1). Table 1. Effect of waterlogging stress and absence of stress (‘no stress’) in soybean plants. Shoot Length Root Length Shoot Fresh Root Fresh RWC (%) (cm/plant) (cm/plant) Weight (g/plant) Weight (g/plant) No Stress NT 22.88  0.88 b 18.07  1.06 a 4.22  0.14 b 2.19  0.09 b 71.7  1.5 a RS 24.08  0.54 a 19.0  1.67 a 6.43  0.52 a 4.60  0.06 a 72.0  1.0 a BC 25.60  0.76 a 19.32  1.21 a 6.69  0.47 a 4.70  0.04 a 72.3  1.2 a Waterlogging Stress NT 19.70  0.73 b 15.04  0.44 b 3.86  0.08 c 1.69  0.24 b 68.3  1.5 b RS 22.80  1.79 a 19.00  0.86 a 4.87  0.18 b 2.45  0.32 a 74.0  1.0 a BC 24.72  0.68 a 19.20  1.10 a 5.00  0.09 a 2.79  0.24 a 76.0  1.0 a Each value represents the mean  SD. Each data point represents the mean of at least three replicates. Different letters in the column after mean values represent the least significant differences at p  0.05. (NT: no treatment; RS: Rhodobacter spaheroides KE149; BC: biochar.) Figure 1. Effect of biochar and R. sphaeroides KE149 on (A) morphological characteristics and (B) color bleaching of soybean plants grown under sufficient water conditions and waterlogging stress. (NT: no treatment; RS: Rhodobacter spaheroides KE149; BC: biochar.) 3.2. Chlorophyll Content The chlorophyll content of the first-, second-, and third-trifoliate leaves was measured. The results showed that KE149 and biochar increased the chlorophyll content by 57% in first-trifoliate leaves, and by similar amounts—namely 142% and 154%, respectively—in second-trifoliate leaves. In third-trifoliate leaves, a vast increase in chlorophyll content was observed for both treatments (Figure 2). Environments 2021, 8, 94 5 of 13 Figure 2. Effect of biochar and R. sphaeroides KE149 inoculation on chlorophyll content in the first-, second-, and third-trifoliate leaves of soybean plants. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress). 3.3. Hormone Quantification ABA: The ABA content significantly dropped by 6% and 25% in plants treated with KE149 and biochar, respectively, under normal stress conditions when compared to no treatment (NT). In contrast, under waterlogging stress, ABA considerably increased by 32% and 33% in plants treated with KE149 and biochar, respectively, compared to NT (Figure 3A). JA: The JA content was significantly increased by 47% and 61% in plants treated with KE149 and biochar, respectively, under normal conditions. However, under stress Environments 2021, 8, 94 6 of 13 conditions it dropped in KE149-treated plants, but it increased in biochar-treated plants (Figure 3B). SA: The SA content was significantly enhanced under normal conditions in plants inoculated with KE149 and biochar. However, under waterlogging stress, biochar appli- cation increased the SA content, whereas no significant differences were observed in the KE149 treatment (Figure 3C). Figure 3. Cont. Environments 2021, 8, 94 7 of 13 Figure 3. Quantification of endogenous phytohormones (A) abscisic acid, (B) jasmonic acid, and (C) salicylic acid content in soybean shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal conditions. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) 3.4. Amino Acid Analysis Proline content was significantly enhanced by 18% and 14% in plants inoculated with KE149 and biochar, respectively, under waterlogging conditions. However, under normal conditions no significant differences were observed. Methionine content increased by 42% and 28% after KE149 and biochar application, respectively, under waterlogging stress. Aspartic acid increased by 233% and 379% in the two treatments, respectively, under stress conditions and, under normal conditions, its contents were enhanced by 72% and 152%, respectively, compared to the control (Figure 4). Figure 4. Cont. Environments 2021, 8, x FOR PEER REVIEW 8 of 13 Environments 2021, 8, 94 8 of 13 No treatment R. sphaeroides KE149 Biochar NS WLS (B) No treatment R. sphaeroides KE149 Biochar NS WLS (C) Figure 4. Quantification of (A) methionine, (B) proline, and (C) aspartic acid content in soybean Figure 4. Quantification of (A) methionine, (B) proline, and (C) aspartic acid content in soybean shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal conditions. Each data point represents the mean of at least three replicates. Error bars represent conditions. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p ≤ 0.05. standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) (NS: no stress; WLS: waterlogging stress.) 3.5. Antioxidant Analysis 3.5. Antioxidant Analysis In the present study, the inoculation of KE149 and biochar significantly enhanced the In the present study, the inoculation of KE149 and biochar significantly enhanced phenolic content by 34% and 15%, respectively, under normal conditions. However, un- the phenolic content by 34% and 15%, respectively, under normal conditions. However, der waterlogging stress conditions, the content of this antioxidant significantly dropped under waterlogging stress conditions, the content of this antioxidant significantly dropped by 24% and 44% in the two treatments, respectively. A similar trend was observed in fla- by 24% and 44% in the two treatments, respectively. A similar trend was observed in vonoid content, which increased by 8% in KE149-treated plants, while no significant dif- flavonoid content, which increased by 8% in KE149-treated plants, while no significant ferences were observed in biochar-treated plants, under normal conditions. However, un- differences were observed in biochar-treated plants, under normal conditions. However, der waterlogging stress, the flavonoid content significantly dropped by 10% and 16% in under waterlogging stress, the flavonoid content significantly dropped by 10% and 16% in KE149- and biochar-treated plants, respectively (Figures 5 and 6). KE149- and biochar-treated plants, respectively (Figures 5 and 6). Aspartic acid content (mg/g, DW) Proline content (mg/g, DW) Environments 2021, 8, 94 9 of 13 Figure 5. Effect of biochar and R. sphaeroides inoculation on the phenolic content of soybean shoots. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) Figure 6. Analysis of flavonoid content in soybean shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal conditions. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) 4. Discussion Biofertilizers are emerging biological tools used for promoting sustainable agriculture and combating threats to the environment. In the present study, the application of the rhizobacterum KE149 and biochar significantly improved plant-growth-promoting traits in soybean plants exposed to waterlogging stress. Here we discuss how KE149 and biochar application regulates various metabolic aspects, such as the functioning of endogenous phytohormones, amino acids, and the antioxidant system of soybean plants subjected to waterlogging stress. A large number of studies reported that ABA maintains water levels in the cell as it controls stomatal activity [38]. In general, low water retention allows guard cells around stomata to close and, at higher moisture levels, it activates the stomatal conductance and stimulates the transpiration rate [39]. In our study, the ABA level was significantly enhanced by the inoculation of biochar and KE149, which might have protected cells from Environments 2021, 8, 94 10 of 13 excess osmotic stress. Our results are in line with those by De Ollas et al. [40], which showed that the ABA level decreased under waterlogging conditions in tomato plants. Similar results were also shown by Arbona et al. [41], who observed a significant drop in the ABA level of Carrizo citrange plant roots exposed to flooding stress. JA is reported to stimulate resistance in plants subjected to stress and is involved in crosstalk for the synthesis of other endogenous phytohormones, as well as amino acids. In the present study, the JA level was significantly enhanced by the application of KE149 and biochar under normal conditions. In contrast, under waterlogging stress, the level dropped after KE149 application, while no significant difference was observed when compared to the control. These results are in line with the findings by Shan et al. [42], who reported that JA application led to the improvement of Agropyron cristatum. Similarly, Yosefi et al. [43] reported that JA was involved in crosstalk with SA to improve water stress resistance in tomatoes. Maladaptive overproduction of JA may reduce plant growth and resistance against stress. Waqas et al. [44] recommended the application of appropriate doses of biochar, after reporting that excessive JA production in rice—following the application of biochar—resulted in physiological abnormalities. Hence, the lower level of of JA in our results indicates the significance of biochar doses on waterlogging stress in soybean plants. SA is reported to induce systemic resistance in plants facing attacks by external pathogens or exposure to abiotic stress [45,46]. Our study showed that SA significantly increased after the application of biochar and KE149, indicating the higher resistance level conferred to the plants (Figure 5). These results are supported by the findings presented in Hayat et al. [47], who reported that the external application of SA improved the physiological status of tomatoes. Similar results have been shown by Sing et al. [48] in wheat. Moreover, our results are validated by various previous studies [49–51] that described the significance of SA in plant toxicity. Amino acids are key components of protein structures, and precursors of hormonal pathways. The crosstalk between endogenous phytohormones is highly influenced by amino acid biosynthesis [52]. Under water stress, proline, methionine, and aspartic acid concentrations play a key role in adjusting the moisture level in plants, and in regulat- ing phytohormones and antioxidants. In general, an increase in proline enhances ABA biosynthesis, which in turn controls the transpiration rate. Our study showed that the proline level significantly increased with biochar and KE149 treatments. A similar trend was observed for aspartic acid and methionine. Proline serves as an osmoregulant and it maintains the redox balance [53]. Similarly, aspartic acid enhances the mobility of amino acids in the phloem [54]. Methionine undergoes a chemical reaction that pro- duces S-adenosylmethionine under the influence of ACC synthase, to finally synthesize ethylene [55]. As ethylene enhances tolerance to prolonged waterlogging stress [56], the observed effect of KE149 and biochar, in terms of amino acid accumulation, possibly trig- gered ethylene synthesis, which might have improved the resistance of plants against waterlogging stress. Water stress generates ROS and imposes osmotic stress on plant cells [57]. To coun- teract or neutralize the negative effects of ROS, plants scavenge radicals [58]. In general, polyphenolic compounds and flavonoids are stimulated in response to biotic/abiotic stresses [57,59]. Their contents have been reported to counterbalance the effects of harmful oxygen radicals [59]. In the present study, the inoculation of KE149 and biochar signifi- cantly enhanced the polyphenol and flavonoid contents under normal conditions, while these decreased considerably under waterlogging stress. The drop in polyphenolic and flavonoid levels indicates the reduced effort made by the plants to combat the negative effects of oxygen radicals. 5. Conclusions The present study shows that the inoculation of biochar and KE149 regulated phyto- hormones and amino acids, and strengthened the antioxidant systems of soybean plants. Environments 2021, 8, 94 11 of 13 Therefore, KE149 and appropriate doses of biochar can be considered as safe, eco-friendly biofertilizers to be used to mitigate waterlogging stress. Author Contributions: Conceptualization, S.-M.K.; Methodology, E.-H.K.; formal analysis, M.A.K.; investigation, E.-H.K. and Y.-S.P.; writing—original draft preparation, A.A.; writing—review and editing, M.A.K.; visualization, supervision, project administration, and funding acquisition; I.-J.L. and S.-M.K. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2020R1I1A1A01065443). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: We would like to acknowledge our deep gratitude to the Kyungpook National University, Department of Applied Biosciences, for providing us with a well-equipped platform with which to undertake our research activities. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. References 1. Khan, M.A.; Asaf, S.; Khan, A.L.; Adhikari, A.; Jan, R.; Ali, S.; Imran, M.; Kim, K.M.; Lee, I.J. Halotolerant rhizobacterial strains mitigate the adverse effects of NaCl stress in soybean seedlings. BioMed Res. Int. 2019, 2019, 9530963. [CrossRef] 2. Bansal, R.; Srivastava, J.P. Antioxidative defense system in pigeonpea roots under waterlogging stress. Acta Physiol. Plant. 2012, 34, 515–522. [CrossRef] 3. Kim, Y.; Shahzad, R.; Lee, I.-J. Regulation of flood stress in plants. In Plant Life under Changing Environment; Elsevier: Amsterdam, The Netherlands, 2020; pp. 157–173. [CrossRef] 4. Hwang, S.-Y.; Lin, H.-W.; Chern, R.-H.; Lo, H.F.; Li, L. Reduced susceptibility to waterlogging together with high-light stress is related to increases in superoxide dismutase and catalase activities in sweet potato. Plant Growth Regul. 1999, 27, 167–172. [CrossRef] 5. Kim, Y.H.; Hwang, S.J.; Waqas, M.; Khan, A.L.; Lee, J.H.; Lee, J.D.; Nguyen, H.T.; Lee, I.J. Comparative analysis of endogenous hormones level in two soybean (Glycine max L.) lines differing in waterlogging tolerance. Front. Plant Sci. 2015, 6, 714. [CrossRef] [PubMed] 6. Egamberdieva, D.; Wirth, S.J.; Alqarawi, A.A.; Abd Allah, E.F.; Hashem, A. Phytohormones and beneficial microbes: Essential components for plants to balance stress and fitness. Front. Microbiol. 2017, 8, 2104. [CrossRef] 7. Yoshida, T.; Christmann, A.; Yamaguchi-Shinozaki, K.; Grill, E.; Fernie, A.R. Revisiting the basal role of ABA–roles outside of stress. Trends Plant Sci. 2019, 24, 625–635. [CrossRef] 8. Kuromori, T.; Seo, M.; Shinozaki, K. ABA transport and plant water stress responses. Trends Plant Sci. 2018, 23, 513–522. [CrossRef] [PubMed] 9. Miura, K.; Tada, Y. Regulation of water, salinity, and cold stress responses by salicylic acid. Front. Plant Sci. 2014, 5, 4. [CrossRef] 10. Wang, J.; Song, L.; Gong, X.; Xu, J.; Li, M. Functions of jasmonic acid in plant regulation and response to abiotic stress. Int. J. Mol. Sci. 2020, 21, 1446. [CrossRef] 11. Das, K.; Roychoudhury, A. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during environmental stress in plants. Front. Environ. Sci. 2014, 2, 53. [CrossRef] 12. Pourcel, L.; Routaboul, J.M.; Cheynier, V.; Lepiniec, L.; Debeaujon, I. Flavonoid oxidation in plants: From biochemical properties to physiological functions. Trends Plant Sci. 2007, 12, 29–36. [CrossRef] 13. Sharma, S.S.; Dietz, K.J. The significance of amino acids and amino acid-derived molecules in plant responses and adaptation to heavy metal stress. J. Exp. Bot. 2006, 57, 711–726. [CrossRef] 14. Lee, K.-E.; Adhikari, A.; Kang, S.-M.; You, Y.-H.; Joo, G.-J.; Kim, J.-H.; Kim, S.-J.; Lee, I.-J. Isolation and characterization of the high silicate and phosphate solubilizing novel strain Enterobacter ludwigii GAK2 that promotes growth in rice plants. Agronomy 2019, 9, 144. [CrossRef] 15. Kubi, H.A.A.; Khan, M.A.; Adhikari, A.; Imran, M.; Kang, S.-M.; Hamayun, M.; Lee, I.-J. Silicon and plant growth-promoting rhizobacteria Pseudomonas psychrotolerans CS51 mitigates salt stress in Zea mays L. Agriculture 2021, 11, 272. [CrossRef] 16. Kazerooni, E.A.; Maharachchikumbura, S.S.N.; Adhikari, A.; Al-Sadi, A.M.; Kang, S.M.; Kim, L.R.; Lee, I.-J. Rhizospheric Bacillus amyloliquefaciens protects Capsicum annuum cv. Geumsugangsan from multiple abiotic stresses via multifarious plant growth-promoting attributes. Front. Plant Sci. 2021, 12, 669693. [CrossRef] Environments 2021, 8, 94 12 of 13 17. Danish, S.; Zafar-ul-Hye, M. Co-application of ACC-deaminase producing PGPR and timber-waste biochar improves pigments formation, growth and yield of wheat under drought stress. Sci. Rep. 2019, 9, 1–13. [CrossRef] 18. Abideen, Z.; Koyro, H.W.; Huchzermeyer, B.; Ansari, R.; Zulfiqar, F.; Gul, B.J.P.B. Ameliorating effects of biochar on photosynthetic efficiency and antioxidant defence of Phragmites karka under drought stress. Plant Biol. 2020, 22, 259–266. [CrossRef] [PubMed] 19. Ren, H.; Lv, C.; Fernández-García, V.; Huang, B.; Yao, J.; Ding, W. Biochar and PGPR amendments influence soil enzyme activities and nutrient concentrations in a eucalyptus seedling plantation. Biomass Convers. Biorefinery 2019, 1–10. [CrossRef] 20. Masciarelli, O.; Llanes, A.; Luna, V. A new PGPR co-inoculated with Bradyrhizobium japonicum enhances soybean nodulation. Microbiol. Res. 2014, 169, 609–615. [CrossRef] 21. Kammann, C.I.; Linsel, S.; Gößling, J.W.; Koyro, H.-W.J.P. Influence of biochar on drought tolerance of Chenopodium quinoa Willd and on soil–plant relations. Plant Soil 2011, 345, 195–210. [CrossRef] 22. Oram, N.J.; van de Voorde, T.F.J.; Ouwehand, G.-J.; Bezemer, T.M.; Mommer, L.; Jeffery, S.; Van Groenigen, J.W.V. Soil amendment with biochar increases the competitive ability of legumes via increased potassium availability. Agric. Ecosyst. Environ. 2014, 191, 92–98. [CrossRef] 23. Jabborova, D.; Wirth, S.; Kannepalli, A.; Narimanov, A.; Desouky, S.; Davranov, K.; Sayyed, R.Z.; El Enshasy, H.; Malek, R.A.; Syed, A.; et al. Co-inoculation of rhizobacteria and biochar application improves growth and nutrientsin soybean and enriches soil nutrients and enzymes. Agronomy 2020, 10, 1142. [CrossRef] 24. Foyer, C.H.; Nguyen, H.; Lam, H.M. Legumes—the art and science of environmentally sustainable agriculture. Plant Cell Environ. 2019, 42, 1–5. [CrossRef] [PubMed] 25. Pampana, S.; Masoni, A.; Arduini, I. Response of cool-season grain legumes to waterlogging at flowering. Can. J. Plant Sci. 2016, 96, 597–603. [CrossRef] 26. Glaeser, J.; Klug, G. Photo-oxidative stress in Rhodobacter sphaeroides: Protective role of carotenoids and expression of selected genes. Microbiology 2005, 151, 1927–1938. [CrossRef] [PubMed] 27. Siebert, C.A.; Qian, P.; Fotiadis, D.; Engel, A.; Hunter, C.N.; Bullough, P.A. Molecular architecture of photosynthetic membranes in Rhodobacter sphaeroides: The role of PufX. EMBO J. 2004, 23, 690–700. [CrossRef] [PubMed] 28. Guo, L.; Zhang, Z.-M.; Lu, D.-T. Effects of Rhodobacter sphaeroides on some physiological-biochemical indexes of wheat seedlings under cadmium stress. J. Agro-Environ. Sci. 2008, 1. 29. Głodowska, M.; Schwinghamer, T.; Husk, B.; Smith, D. Biochar based inoculants improve soybean growth and nodulation. Agric. Sci. 2017, 08, 1048–1064. [CrossRef] 30. Kang, S.-M.; Adhikari, A.; Lee, K.-E.; Khan, M.A.; Shahzad, R.; Dhungana, S.K.; Lee, I.-J. Inoculation with Indole-3-acetic acid-producing rhizospheric Rhodobacter sphaeroides KE149 augments growth of adzuki bean plants under water stress. J. Microbiol. Biotechnol. 2020, 30, 717–725. [CrossRef] 31. Wattoo, F.M.; Rana, R.M.; Fiaz, S.; Zafar, S.A.; Noor, M.A.; Hassan, H.M.; Bhatti, M.H.; Rehman, S.U.; Anis, G.B.; Amir, R.M. Identification of drought tolerant maize genotypes and seedling based morpho-physiological selection indices for crop improvement. Sains Malays. 2018, 47, 295–302. 32. Bhusal, N.; Lee, M.; Lee, H.; Adhikari, A.; Han, A.R.; Han, A.; Kim, H.S. Evaluation of morphological, physiological, and biochemical traits for assessing drought resistance in eleven tree species. Sci. Total Environ. 2021, 779, 146466. [CrossRef] 33. Adhikari, A.; Lee, K.E.; Khan, M.A.; Kang, S.M.; Adhikari, B.; Imran, M.; Jan, R.; Kim, K.M.; Lee, I.J. Effect of silicate and phosphate solubilizing Rhizobacterium Enterobacter ludwigii GAK2 on Oryza sativa L. under cadmium stress. J. Microbiol. Biotechnol. 2020, 30, 118–126. [CrossRef] 34. Adhikari, A.; Khan, M.A.; Lee, K.E.; Kang, S.M.; Dhungana, S.K.; Bhusal, N.; Lee, I.-J. The halotolerant Rhizobacterium— Pseudomonas koreensis MU2 enhances inorganic silicon and phosphorus use efficiency and augments salt stress tolerance in soybean (Glycine max L.). Microorganisms 2020, 8, 1256. [CrossRef] 35. Shahzad, R.; Khan, A.L.; Bilal, S.; Asaf, S.; Lee, I.-J. Plant growth-promoting endophytic bacteria versus pathogenic infections: An example of Bacillus amyloliquefaciens RWL-1 and Fusarium oxysporum f. sp. lycopersici in tomato. Peer J. 2017, 5, e3107. [CrossRef] [PubMed] 36. Adhikari, B.; Dhungana, S.K.; Waqas Ali, M.W.; Adhikari, A.; Kim, I.-D.; Shin, D.-H. Antioxidant activities, polyphenol, flavonoid, and amino acid contents in peanut shell. J. Saudi Soc. Agric. Sci. 2019, 18, 437–442. [CrossRef] 37. Adhikari, B.; Dhungana, S.K.; Ali, M.W.; Adhikari, A.; Kim, I.D.; Shin, D.H. Resveratrol, total phenolic and flavonoid contents, and antioxidant potential of seeds and sprouts of Korean peanuts. Food Sci. Biotechnol. 2018, 27, 1275–1284. [CrossRef] [PubMed] 38. Maheshwari, P.; Assmann, S.M.; Albert, R. A guard cell abscisic acid (ABA) network model that captures the stomatal resting state. Front. Physiol. 2020, 11, 927. [CrossRef] [PubMed] 39. Jacob, T.; Ritchie, S.; Assmann, S.M.; Gilroy, S. Abscisic acid signal transduction in guard cells is mediated by phospholipase D activity. Proc. Natl. Acad. Sci. USA 1999, 96, 12192–12197. [CrossRef] 40. De Ollas, C.; González-Guzmán, M.; Pitarch, Z.; Matus, J.T.; Candela, H.; Rambla, J.L.; Granell, A.; Gómez-Cadenas, A.; Arbona, V. Identification of ABA-mediated genetic and metabolic responses to soil flooding in tomato (Solanum lycopersicum L. mill). Front. Plant Sci. 2021, 12, 613059. [CrossRef] 41. Arbona, V.; Zandalinas, S.I.; Manzi, M.; González-Guzmán, M.; Rodriguez, P.L.; Gómez-Cadenas, A. Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf.  Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors. Plant Mol. Biol. 2017, 93, 623–640. [CrossRef] Environments 2021, 8, 94 13 of 13 42. Shan, C.; Liang, Z. Jasmonic acid regulates ascorbate and glutathione metabolism in Agropyron cristatum leaves under water stress. Plant Sci. 2010, 178, 130–139. [CrossRef] 43. Yosefi, A.; Mozafari, A.; Javadi, T. Jasmonic acid improved in vitro strawberry (Fragaria  ananassa Duch.) resistance to PEG- induced water stress. Plant Cell Tissue Organ Cult. (PCTOC) 2020, 142, 549–558. [CrossRef] 44. Waqas, M.; Shahzad, R.; Hamayun, M.; Asaf, S.; Khan, A.L.; Kang, S.M.; Yun, S.; Kim, K.M.; Lee, I.J. Biochar amendment changes jasmonic acid levels in two rice varieties and alters their resistance to herbivory. PLoS ONE 2018, 13, e0191296. [CrossRef] [PubMed] 45. Zhang, S.; Moyne, A.-L.; Reddy, M.S.; Kloepper, J.W. The role of salicylic acid in induced systemic resistance elicited by plant growth-promoting rhizobacteria against blue mold of tobacco. Biol. Control. 2002, 25, 288–296. [CrossRef] 46. De Vleesschauwer, D.; Djavaheri, M.; Bakker, P.A.; Höfte, M. Pseudomonas fluorescens WCS374r-induced systemic resistance in rice against Magnaporthe oryzae is based on pseudobactin-mediated priming for a salicylic acid-repressible multifaceted defense response. Plant Physiol. 2008, 148, 1996–2012. [CrossRef] [PubMed] 47. Hayat, S.; Hasan, S.A.; Fariduddin, Q.; Ahmad, A.J. Growth of tomato (Lycopersicon esculentum) in response to salicylic acid under water stress. J. Plant Interact. 2008, 3, 297–304. [CrossRef] 48. Singh, B.; Usha, K. Salicylic acid induced physiological and biochemical changes in wheat seedlings under water stress. Plant Growth Regul. 2003, 39, 137–141. [CrossRef] 49. Yang, Y.; Qi, M.; Mei, C. Endogenous salicylic acid protects rice plants from oxidative damage caused by aging as well as biotic and abiotic stress. Plant J. Cell Mol. Biol. 2004, 40, 909–919. [CrossRef] [PubMed] 50. Sakhabutdinova, A.; Fatkhutdinova, D.; Bezrukova, M.; Shakirova, F. Salicylic acid prevents the damaging action of stress factors on wheat plants. Bulg. J. Plant Physiol. 2003, 21, 314–319. 51. Liu, Z.; Ding, Y.; Wang, F.; Ye, Y.; Zhu, C.J. Role of salicylic acid in resistance to cadmium stress in plants. Plant Cell Rep. 2016, 35, 719–731. [CrossRef] 52. Waqas, M.; Khan, A.L.; Kamran, M.; Hamayun, M.; Kang, S.M.; Kim, Y.H.; Lee, I.-J. Endophytic fungi produce gibberellins and indoleacetic acid and promotes host-plant growth during stress. Molecules 2012, 17, 10754–10773. [CrossRef] 53. Li, Z.; Yong, B.; Cheng, B.; Wu, X.; Zhang, Y.; Zhang, X.; Peng, Y.J. Nitric oxide, -aminobutyric acid, and mannose pretreatment influence metabolic profiles in white clover under water stress. J. Integr. Plant Biol. 2019, 61, 1255–1273. [CrossRef] [PubMed] 54. Farhangi-Abriz, S.; Faegi-Analou, R.; Nikpour-Rashidabad, N.J. Polyamines, affected the nitrogen partitioning, protein accumula- tion and amino acid composition of mung bean under water stress. J. Crop. Sci. Biotechnol. 2017, 20, 279–285. [CrossRef] 55. Vwioko, E.; Adinkwu, O.; El-Esawi, M.A. Comparative physiological, biochemical, and genetic responses to prolonged waterlog- ging stress in okra and maize given exogenous ethylene priming. Front. Physiol. 2017, 8, 632. [CrossRef] [PubMed] 56. Kim, Y.; Seo, C.W.; Khan, A.L.; Mun, B.G.; Shahzad, R.; Ko, J.W.; Yun, B.W.; Park, S.K.; Lee, I.J. exo-ethylene application mitigates waterlogging stress in soybean (Glycine max L.). BMC Plant Biol. 2018, 18, 254. [CrossRef] 57. Haddadi, B.S.; Hassanpour, H.; Niknam, V. Effect of salinity and waterlogging on growth, anatomical and antioxidative responses in Mentha aquatica L. Acta Physiol. Plant. 2016, 38, 119. [CrossRef] 58. Ksouri, R.; Megdiche, W.; Debez, A.; Falleh, H.; Grignon, C.; Abdelly, C. Salinity effects on polyphenol content and antioxidant activities in leaves of the halophyte Cakile maritima. Plant Physiol. Biochem. 2007, 45, 244–249. [CrossRef] 59. Giorgi, A.; Mingozzi, M.; Madeo, M.; Speranza, G.; Cocucci, M. Effect of nitrogen starvation on the phenolic metabolism and antioxidant properties of yarrow (Achillea collina Becker ex Rchb.). Food Chem. 2009, 114, 204–211. [CrossRef] http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environments Multidisciplinary Digital Publishing Institute

Influence of the Rhizobacterium Rhodobacter sphaeroides KE149 and Biochar on Waterlogging Stress Tolerance in Glycine max L.

Download PDF
13 pages

Loading next page...
 
/lp/multidisciplinary-digital-publishing-institute/influence-of-the-rhizobacterium-rhodobacter-sphaeroides-ke149-and-6BG0eVcB7H

References

References for this paper are not available at this time. We will be adding them shortly, thank you for your patience.

Publisher
Multidisciplinary Digital Publishing Institute
Copyright
© 1996-2021 MDPI (Basel, Switzerland) unless otherwise stated Disclaimer The statements, opinions and data contained in the journals are solely those of the individual authors and contributors and not of the publisher and the editor(s). MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Terms and Conditions Privacy Policy
ISSN
2076-3298
DOI
10.3390/environments8090094
Publisher site
See Article on Publisher Site

Abstract

environments Article Influence of the Rhizobacterium Rhodobacter sphaeroides KE149 and Biochar on Waterlogging Stress Tolerance in Glycine max L. Sang-Mo Kang, Arjun Adhikari , Muhammad Aaqil Khan , Eun-Hae Kwon, Yong-Sung Park and In-Jung Lee * Department of Applied Biosciences, Kyungpook National University, 80 Daehakro, Bukgu, Daegu 41566, Korea; kmoya@hanmail.net (S.-M.K.); farmerarjun7@gmail.com (A.A.); aqil_bacha@yahoo.com (M.A.K.); eunhaekwon@naver.com (E.-H.K.); Pjyjsj3@gmail.com (Y.-S.P.) * Correspondence: ijlee@knu.ac.kr; Tel.: +82-53-950-5708 Abstract: In the context of the current climate change and increasing population scenarios, wa- terlogging stress in plants represents a global threat to sustainable agriculture production. Plant- growth-promoting rhizobacteria and biochar have been widely reported to mitigate the effects of several abiotic stresses. Hence, in the present study, we examined the effect of the rhizobacterium Rhodobacter sphaeroides KE149 and biochar on soybean plants subjected to sufficient water supply and waterlogging stress conditions. Our results revealed that KE149 and biochar inoculation significantly improved plant morphological attributes, such as root length, shoot length, and fresh biomass. The biochemical analysis results showed that the two treatments determined a significant drop in the levels of endogenous phytohormones (such as abscisic acid) under normal conditions, which were considerably enhanced under waterlogging stress. However, the jasmonic acid content increased with Citation: Kang, S.-M.; Adhikari, A.; the application of biochar and KE149 under normal conditions, and it considerably decreased under Khan, M.A.; Kwon, E.-H.; Park, Y.-S.; waterlogging stress. Moreover, proline, methionine, and aspartic acid were significantly increased, Lee, I.-J. Influence of the whereas the phenolic and flavonoid contents were reduced with the application of the two treatments Rhizobacterium Rhodobacter under waterlogging stress. These results suggest that the application of KE149 and biochar can be sphaeroides KE149 and Biochar on a safe biological tool with which to improve the physiology and productivity of soybean plants Waterlogging Stress Tolerance in exposed to waterlogging stress. Glycine max L. Environments 2021, 8, 94. https://doi.org/10.3390/ environments8090094 Keywords: biochar; soybean; Rhodobacter sphaeroides KE149; waterlogging; abiotic stress Academic Editor: Wen-tien Tsai Received: 6 August 2021 1. Introduction Accepted: 13 September 2021 Exposure to abiotic stress is one of the major causes of low productivity of agricul- Published: 15 September 2021 tural crops, and [1] waterlogging stress, in particular, is prevalent globally in agriculture sites [2]. Climate change, influenced by massive anthropogenic human activities, has Publisher’s Note: MDPI stays neutral further triggered water stress in lands used for agricultural production. In general, water with regard to jurisdictional claims in stress is categorized as (i) water deficiency and (ii) excess water exposure, which includes published maps and institutional affil- waterlogging and complete submergence [3]. Plants face several physiological abnormal- iations. ities when subjected to water stress. The main processes induced are the generation of reactive oxygen species (ROS) in cells, ionic imbalance, electrolytic leakage, and osmotic stress, which all ultimately result in cell death. To counteract these stress reactions, the plant undergoes several functional changes that include molecule signaling, antioxidant Copyright: © 2021 by the authors. production, phytohormone modulation, and amino acid biosynthesis [3–5]. Licensee MDPI, Basel, Switzerland. Phytohormones such as abscisic acid (ABA), jasmonic acid (JA), and salicylic acid (SA) This article is an open access article are widely reported as being associated with stress tolerance [6]. ABA plays a key role in distributed under the terms and the regulation of stomata to confer water stress resistance [7,8], SA is a natural phenolic conditions of the Creative Commons compound that activates the defense system against pathogens and abiotic stresses [9], and Attribution (CC BY) license (https:// JA induces defense mechanisms, in addition to activating antioxidants and participating in creativecommons.org/licenses/by/ amino acid accumulation and cross-signaling [10]. 4.0/). Environments 2021, 8, 94. https://doi.org/10.3390/environments8090094 https://www.mdpi.com/journal/environments Environments 2021, 8, 94 2 of 13 Antioxidants play a key role in minimizing the detrimental effects of oxygen radi- cals generated in plant cells in response to abiotic stress [11]. Among the antioxidants, flavonoids are known to improve yield quality, while phenolic compounds are known to scavenge ions to neutralize ROS [12]. Similarly, the amino-acid-like proline, methionine, and aspartic acid are actively involved in metal sequestration, radical scavengers, stabi- lizers of macromolecules, electron sinks, and manufacturing cell wall components [13]. Therefore, it is vital to improve plants’ physiological aspects under stress in order to achieve optimal crop production. Plant-growth-promoting rhizobacteria (PGPR) and biochar are emerging biostimulants that have been reported to improve metabolism and confer tolerance in crops subjected to several biotic and abiotic stresses [14,15]. Biochar and PGPR are biologically safe tools, and they work symbiotically to improve plant metabolism. The functional aspects of PGPR include the production of secondary metabolites, ion regulation, the improvement of ion absorption through roots, and translocation to shoots [16,17]. Similarly, biochar replenishes the soil, enhances carbon sequestration, and facilitates microbial growth [18,19]. Numerous studies have reported the beneficial role of PGPR application for plant growth and development [20]. In addition, Abideen et al. [18] showed that biochar application improved the growth of Phragmites karka under water stress conditions, and Kammann et al. [21] reported that appropriate doses of biochar improved the growth of Chenopodium quinoa, also subjected to water stress. Moreover, PGPR and biochar are widely known to improve the growth of several leguminous crops [22,23]. Leguminous plants are highly prone to waterlogging stress [24,25]. The photosynthetic activity of Rhodobacter spp. has been widely reported to mitigate stress in plants [26–28], and biochar is recognized as a stress reliever and growth promoter [29]. Considering these facts, the aim of the present study is to understand the metabolomic perspectives of soybean plants treated with biochar and the plant-growth-promoting bacterium Rhodobac- ter sphaeroides KE149, during exposure to waterlogging stress. The tested hypothesis is that PGPR and biochar have a potential role in regulating ion absorption through roots, regulating phytohormones, and amino acid synthesis in soybean plants exposed to waterlogging stress. 2. Materials and Methods 2.1. Selection of Microbes The bacterium Rhodobacter sphaeroides KE149 was selected for the current experiment based on the results obtained from our previous study, where KE149 was reported to have various plant-growth-promoting traits, including the ability to confer resistance against water stress in adzuki bean plants [30]. 2.2. Experiment Location, Method, and Design The experiment was conducted at the greenhouse of Kyungpook National University, Daegu, Korea, located at longitude 128.587655 E and latitude 35.857655 N. Soybean (Glycine max L. cv. Taekwang) seeds were surface-sterilized with 1% Tween solution and 2% perchloric acid, and were washed thoroughly with sterile distilled water. The seeds were then sown into pots filled with autoclaved soil containing peat moss (13–18%), perlite (7–11%), coco-peat (63–68%), and zeolite (6–8%), with the following macro-nutrients: NH ~90 mg/kg, NO ~205 mg/kg, P O ~350 mg/kg, and K O~100 mg/kg. Three- 4 3 2 5 2 week-old soybean plants (50 per treatment) were treated with 10 mL of bacterial culture 8 –1 (10 CFUmL ) and oak wood biochar (0.1% per pot). The biochar consisted of dolomite 10%, zeolite 5%, molasses 10%, peat 5%, and diameter 3–4 mm. Seven days later, soybean plants, with and without bacterial treatment, were subjected to waterlogging stress. The pots were kept in a tray and water was applied on daily basis to maintain the water level up to 5 cm above the soil surface. The experiment was designed as no stress (NS) and waterlogging stress (WLS). The length and fresh weight of shoots and roots in addition Environments 2021, 8, 94 3 of 13 to chlorophyll content were measured after 7 days of waterlogging treatment, and plant samples were collected for further biochemical analyses. 2.3. Measurement of Realtive Water Content and Chlorophyll Content The relative water content (RWC) was measured according to the method described by Wattoo [31]. The chlorophyll content was measured by using a CCM-300 chlorophyll content meter (Opti-Sciences, Hudson, NH). This instrument uses a fiber optic probe that detects the emission rate of red to far-red fluorescence (700 nm to 735 nm) [30]. 2.4. Quantification of Endogenous Phytohormones ABA: The method described by Bhusal et al. [32] was used to quantify the ABA content in plant shoots. In brief, one gram of freeze-dried sample was extracted with isopropanol and acetic acid (95:5 v/v). The obtained solution was filtered and an internal standard [()-3,5,5,7,7,7-d6)-ABA] was added. The extract was washed with 1 N NaOH and chlorophyll was separated by CH CL . Subsequently, polyvinylpolypyrrolidone was 2 2 added and the solution was stirred for an hour; then it was filtered, evaporated, and finally extracted through ethyl acetate/diethyl ether. The ABA extracts were analyzed by GC-MS/SIM (6890 N Network GC System and 5973 Network Mass Selective Detector; Agilent Technologies, Santa Clara, CA, USA). JA: The protocol described in Adhikari et al. [33] was used to obtain the JA extract. In brief, one gram of freeze-dried ground sample was extracted using acetone/citric acid (70:30 v/v) and filtered. The (9,10– H )-9,10- Dihydro-JA (100 ng) was added as an internal standard. Methylation was performed using diethyl ether followed by dichloromethane. The peaks were obtained using GC-MS/SIM technology (6890 N Network GC System and 5973 Network Mass Selective Detector; Agilent Technologies, Santa Clara, CA, USA). SA: SA was quantified based on the method used by Adhikari et al. [34]. In brief, 0.5 g of lyophilized sample was extracted with 100% methanol, was centrifuged, and the solution obtained was vacuum-dried and suspended in trichloroacetic acid (5%). The solution was then partitioned by cyclopentane, ethyl acetate, and isopropanol, and subsequently it was dried using N . The excitation and emission peaks at 305 nm and 355 nm were recorded respectively using HPLC (Shimadzu RF-10AXL fluorescence detector). 2.5. Amino Acid and Antioxidant Analyses The method described by Shahzad et al. [35] was used to quantify the amino acid content in soybean shoots. In brief, 0.05 g of lyophilized sample was suspended with 6 N HCl and charged with N . The sample was kept airtight at 110 C on a hot plate for 24 h and was dried at 80 C for the next 24 h. The extract was obtained with 0.02 N hydrochloric acid and injected into an amino acid auto-analyzer (Hitachi, Japan). For the analysis of antioxidants, phenolic and flavonoid contents were measured based on the methods described by Adhikari et al. [36] and Adhikari et al. [37], respectively. 2.6. Statistical Analysis The present study was conducted using a completely randomized design with six replicates for each treatment. The data were analyzed in SAS 9.4 (SAS Institute, Cary, NC, USA) and evaluated using Duncan’s multiple range test (DMRT) at p  0.05. 3. Results 3.1. Effect on Morphological Attributes and Relative Water Content The inoculation of KE149 and biochar in soybean improved morphological character- istics such as root and shoot length as well as total biomass. Under normal conditions, the plants treated with KE149 and biochar showed a 52% and 58% increase, respectively, in shoot weight. A similar trend was observed under waterlogging conditions, where the shoot weight increased by 26% and 29%, respectively in the two treatments. Minor differ- ences were observed in shoot and root lengths under normal conditions. However, under Environments 2021, 8, 94 4 of 13 waterlogging conditions, shoot length increased by 15% and 25% in the two treatments, respectively, and root length increased by 26% and 27%, also respectively (Table 1 and Figure 1). Table 1. Effect of waterlogging stress and absence of stress (‘no stress’) in soybean plants. Shoot Length Root Length Shoot Fresh Root Fresh RWC (%) (cm/plant) (cm/plant) Weight (g/plant) Weight (g/plant) No Stress NT 22.88  0.88 b 18.07  1.06 a 4.22  0.14 b 2.19  0.09 b 71.7  1.5 a RS 24.08  0.54 a 19.0  1.67 a 6.43  0.52 a 4.60  0.06 a 72.0  1.0 a BC 25.60  0.76 a 19.32  1.21 a 6.69  0.47 a 4.70  0.04 a 72.3  1.2 a Waterlogging Stress NT 19.70  0.73 b 15.04  0.44 b 3.86  0.08 c 1.69  0.24 b 68.3  1.5 b RS 22.80  1.79 a 19.00  0.86 a 4.87  0.18 b 2.45  0.32 a 74.0  1.0 a BC 24.72  0.68 a 19.20  1.10 a 5.00  0.09 a 2.79  0.24 a 76.0  1.0 a Each value represents the mean  SD. Each data point represents the mean of at least three replicates. Different letters in the column after mean values represent the least significant differences at p  0.05. (NT: no treatment; RS: Rhodobacter spaheroides KE149; BC: biochar.) Figure 1. Effect of biochar and R. sphaeroides KE149 on (A) morphological characteristics and (B) color bleaching of soybean plants grown under sufficient water conditions and waterlogging stress. (NT: no treatment; RS: Rhodobacter spaheroides KE149; BC: biochar.) 3.2. Chlorophyll Content The chlorophyll content of the first-, second-, and third-trifoliate leaves was measured. The results showed that KE149 and biochar increased the chlorophyll content by 57% in first-trifoliate leaves, and by similar amounts—namely 142% and 154%, respectively—in second-trifoliate leaves. In third-trifoliate leaves, a vast increase in chlorophyll content was observed for both treatments (Figure 2). Environments 2021, 8, 94 5 of 13 Figure 2. Effect of biochar and R. sphaeroides KE149 inoculation on chlorophyll content in the first-, second-, and third-trifoliate leaves of soybean plants. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress). 3.3. Hormone Quantification ABA: The ABA content significantly dropped by 6% and 25% in plants treated with KE149 and biochar, respectively, under normal stress conditions when compared to no treatment (NT). In contrast, under waterlogging stress, ABA considerably increased by 32% and 33% in plants treated with KE149 and biochar, respectively, compared to NT (Figure 3A). JA: The JA content was significantly increased by 47% and 61% in plants treated with KE149 and biochar, respectively, under normal conditions. However, under stress Environments 2021, 8, 94 6 of 13 conditions it dropped in KE149-treated plants, but it increased in biochar-treated plants (Figure 3B). SA: The SA content was significantly enhanced under normal conditions in plants inoculated with KE149 and biochar. However, under waterlogging stress, biochar appli- cation increased the SA content, whereas no significant differences were observed in the KE149 treatment (Figure 3C). Figure 3. Cont. Environments 2021, 8, 94 7 of 13 Figure 3. Quantification of endogenous phytohormones (A) abscisic acid, (B) jasmonic acid, and (C) salicylic acid content in soybean shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal conditions. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) 3.4. Amino Acid Analysis Proline content was significantly enhanced by 18% and 14% in plants inoculated with KE149 and biochar, respectively, under waterlogging conditions. However, under normal conditions no significant differences were observed. Methionine content increased by 42% and 28% after KE149 and biochar application, respectively, under waterlogging stress. Aspartic acid increased by 233% and 379% in the two treatments, respectively, under stress conditions and, under normal conditions, its contents were enhanced by 72% and 152%, respectively, compared to the control (Figure 4). Figure 4. Cont. Environments 2021, 8, x FOR PEER REVIEW 8 of 13 Environments 2021, 8, 94 8 of 13 No treatment R. sphaeroides KE149 Biochar NS WLS (B) No treatment R. sphaeroides KE149 Biochar NS WLS (C) Figure 4. Quantification of (A) methionine, (B) proline, and (C) aspartic acid content in soybean Figure 4. Quantification of (A) methionine, (B) proline, and (C) aspartic acid content in soybean shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal conditions. Each data point represents the mean of at least three replicates. Error bars represent conditions. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p ≤ 0.05. standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) (NS: no stress; WLS: waterlogging stress.) 3.5. Antioxidant Analysis 3.5. Antioxidant Analysis In the present study, the inoculation of KE149 and biochar significantly enhanced the In the present study, the inoculation of KE149 and biochar significantly enhanced phenolic content by 34% and 15%, respectively, under normal conditions. However, un- the phenolic content by 34% and 15%, respectively, under normal conditions. However, der waterlogging stress conditions, the content of this antioxidant significantly dropped under waterlogging stress conditions, the content of this antioxidant significantly dropped by 24% and 44% in the two treatments, respectively. A similar trend was observed in fla- by 24% and 44% in the two treatments, respectively. A similar trend was observed in vonoid content, which increased by 8% in KE149-treated plants, while no significant dif- flavonoid content, which increased by 8% in KE149-treated plants, while no significant ferences were observed in biochar-treated plants, under normal conditions. However, un- differences were observed in biochar-treated plants, under normal conditions. However, der waterlogging stress, the flavonoid content significantly dropped by 10% and 16% in under waterlogging stress, the flavonoid content significantly dropped by 10% and 16% in KE149- and biochar-treated plants, respectively (Figures 5 and 6). KE149- and biochar-treated plants, respectively (Figures 5 and 6). Aspartic acid content (mg/g, DW) Proline content (mg/g, DW) Environments 2021, 8, 94 9 of 13 Figure 5. Effect of biochar and R. sphaeroides inoculation on the phenolic content of soybean shoots. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) Figure 6. Analysis of flavonoid content in soybean shoots following inoculation with R. spharoides KE149 and biochar under waterlogging and normal conditions. Each data point represents the mean of at least three replicates. Error bars represent standard deviations. Bars with different letters are significantly different from each other at p  0.05. (NS: no stress; WLS: waterlogging stress.) 4. Discussion Biofertilizers are emerging biological tools used for promoting sustainable agriculture and combating threats to the environment. In the present study, the application of the rhizobacterum KE149 and biochar significantly improved plant-growth-promoting traits in soybean plants exposed to waterlogging stress. Here we discuss how KE149 and biochar application regulates various metabolic aspects, such as the functioning of endogenous phytohormones, amino acids, and the antioxidant system of soybean plants subjected to waterlogging stress. A large number of studies reported that ABA maintains water levels in the cell as it controls stomatal activity [38]. In general, low water retention allows guard cells around stomata to close and, at higher moisture levels, it activates the stomatal conductance and stimulates the transpiration rate [39]. In our study, the ABA level was significantly enhanced by the inoculation of biochar and KE149, which might have protected cells from Environments 2021, 8, 94 10 of 13 excess osmotic stress. Our results are in line with those by De Ollas et al. [40], which showed that the ABA level decreased under waterlogging conditions in tomato plants. Similar results were also shown by Arbona et al. [41], who observed a significant drop in the ABA level of Carrizo citrange plant roots exposed to flooding stress. JA is reported to stimulate resistance in plants subjected to stress and is involved in crosstalk for the synthesis of other endogenous phytohormones, as well as amino acids. In the present study, the JA level was significantly enhanced by the application of KE149 and biochar under normal conditions. In contrast, under waterlogging stress, the level dropped after KE149 application, while no significant difference was observed when compared to the control. These results are in line with the findings by Shan et al. [42], who reported that JA application led to the improvement of Agropyron cristatum. Similarly, Yosefi et al. [43] reported that JA was involved in crosstalk with SA to improve water stress resistance in tomatoes. Maladaptive overproduction of JA may reduce plant growth and resistance against stress. Waqas et al. [44] recommended the application of appropriate doses of biochar, after reporting that excessive JA production in rice—following the application of biochar—resulted in physiological abnormalities. Hence, the lower level of of JA in our results indicates the significance of biochar doses on waterlogging stress in soybean plants. SA is reported to induce systemic resistance in plants facing attacks by external pathogens or exposure to abiotic stress [45,46]. Our study showed that SA significantly increased after the application of biochar and KE149, indicating the higher resistance level conferred to the plants (Figure 5). These results are supported by the findings presented in Hayat et al. [47], who reported that the external application of SA improved the physiological status of tomatoes. Similar results have been shown by Sing et al. [48] in wheat. Moreover, our results are validated by various previous studies [49–51] that described the significance of SA in plant toxicity. Amino acids are key components of protein structures, and precursors of hormonal pathways. The crosstalk between endogenous phytohormones is highly influenced by amino acid biosynthesis [52]. Under water stress, proline, methionine, and aspartic acid concentrations play a key role in adjusting the moisture level in plants, and in regulat- ing phytohormones and antioxidants. In general, an increase in proline enhances ABA biosynthesis, which in turn controls the transpiration rate. Our study showed that the proline level significantly increased with biochar and KE149 treatments. A similar trend was observed for aspartic acid and methionine. Proline serves as an osmoregulant and it maintains the redox balance [53]. Similarly, aspartic acid enhances the mobility of amino acids in the phloem [54]. Methionine undergoes a chemical reaction that pro- duces S-adenosylmethionine under the influence of ACC synthase, to finally synthesize ethylene [55]. As ethylene enhances tolerance to prolonged waterlogging stress [56], the observed effect of KE149 and biochar, in terms of amino acid accumulation, possibly trig- gered ethylene synthesis, which might have improved the resistance of plants against waterlogging stress. Water stress generates ROS and imposes osmotic stress on plant cells [57]. To coun- teract or neutralize the negative effects of ROS, plants scavenge radicals [58]. In general, polyphenolic compounds and flavonoids are stimulated in response to biotic/abiotic stresses [57,59]. Their contents have been reported to counterbalance the effects of harmful oxygen radicals [59]. In the present study, the inoculation of KE149 and biochar signifi- cantly enhanced the polyphenol and flavonoid contents under normal conditions, while these decreased considerably under waterlogging stress. The drop in polyphenolic and flavonoid levels indicates the reduced effort made by the plants to combat the negative effects of oxygen radicals. 5. Conclusions The present study shows that the inoculation of biochar and KE149 regulated phyto- hormones and amino acids, and strengthened the antioxidant systems of soybean plants. Environments 2021, 8, 94 11 of 13 Therefore, KE149 and appropriate doses of biochar can be considered as safe, eco-friendly biofertilizers to be used to mitigate waterlogging stress. Author Contributions: Conceptualization, S.-M.K.; Methodology, E.-H.K.; formal analysis, M.A.K.; investigation, E.-H.K. and Y.-S.P.; writing—original draft preparation, A.A.; writing—review and editing, M.A.K.; visualization, supervision, project administration, and funding acquisition; I.-J.L. and S.-M.K. All authors have read and agreed to the published version of the manuscript. Funding: This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF), funded by the Ministry of Education (2020R1I1A1A01065443). Institutional Review Board Statement: Not applicable. Informed Consent Statement: Not applicable. Data Availability Statement: Not applicable. Acknowledgments: We would like to acknowledge our deep gratitude to the Kyungpook National University, Department of Applied Biosciences, for providing us with a well-equipped platform with which to undertake our research activities. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; or in the decision to publish the results. References 1. Khan, M.A.; Asaf, S.; Khan, A.L.; Adhikari, A.; Jan, R.; Ali, S.; Imran, M.; Kim, K.M.; Lee, I.J. Halotolerant rhizobacterial strains mitigate the adverse effects of NaCl stress in soybean seedlings. BioMed Res. Int. 2019, 2019, 9530963. [CrossRef] 2. Bansal, R.; Srivastava, J.P. Antioxidative defense system in pigeonpea roots under waterlogging stress. Acta Physiol. Plant. 2012, 34, 515–522. [CrossRef] 3. Kim, Y.; Shahzad, R.; Lee, I.-J. Regulation of flood stress in plants. In Plant Life under Changing Environment; Elsevier: Amsterdam, The Netherlands, 2020; pp. 157–173. [CrossRef] 4. Hwang, S.-Y.; Lin, H.-W.; Chern, R.-H.; Lo, H.F.; Li, L. Reduced susceptibility to waterlogging together with high-light stress is related to increases in superoxide dismutase and catalase activities in sweet potato. Plant Growth Regul. 1999, 27, 167–172. [CrossRef] 5. Kim, Y.H.; Hwang, S.J.; Waqas, M.; Khan, A.L.; Lee, J.H.; Lee, J.D.; Nguyen, H.T.; Lee, I.J. Comparative analysis of endogenous hormones level in two soybean (Glycine max L.) lines differing in waterlogging tolerance. Front. Plant Sci. 2015, 6, 714. [CrossRef] [PubMed] 6. Egamberdieva, D.; Wirth, S.J.; Alqarawi, A.A.; Abd Allah, E.F.; Hashem, A. Phytohormones and beneficial microbes: Essential components for plants to balance stress and fitness. Front. Microbiol. 2017, 8, 2104. [CrossRef] 7. Yoshida, T.; Christmann, A.; Yamaguchi-Shinozaki, K.; Grill, E.; Fernie, A.R. Revisiting the basal role of ABA–roles outside of stress. Trends Plant Sci. 2019, 24, 625–635. [CrossRef] 8. Kuromori, T.; Seo, M.; Shinozaki, K. ABA transport and plant water stress responses. Trends Plant Sci. 2018, 23, 513–522. [CrossRef] [PubMed] 9. Miura, K.; Tada, Y. Regulation of water, salinity, and cold stress responses by salicylic acid. Front. Plant Sci. 2014, 5, 4. [CrossRef] 10. Wang, J.; Song, L.; Gong, X.; Xu, J.; Li, M. Functions of jasmonic acid in plant regulation and response to abiotic stress. Int. J. Mol. Sci. 2020, 21, 1446. [CrossRef] 11. Das, K.; Roychoudhury, A. Reactive oxygen species (ROS) and response of antioxidants as ROS-scavengers during environmental stress in plants. Front. Environ. Sci. 2014, 2, 53. [CrossRef] 12. Pourcel, L.; Routaboul, J.M.; Cheynier, V.; Lepiniec, L.; Debeaujon, I. Flavonoid oxidation in plants: From biochemical properties to physiological functions. Trends Plant Sci. 2007, 12, 29–36. [CrossRef] 13. Sharma, S.S.; Dietz, K.J. The significance of amino acids and amino acid-derived molecules in plant responses and adaptation to heavy metal stress. J. Exp. Bot. 2006, 57, 711–726. [CrossRef] 14. Lee, K.-E.; Adhikari, A.; Kang, S.-M.; You, Y.-H.; Joo, G.-J.; Kim, J.-H.; Kim, S.-J.; Lee, I.-J. Isolation and characterization of the high silicate and phosphate solubilizing novel strain Enterobacter ludwigii GAK2 that promotes growth in rice plants. Agronomy 2019, 9, 144. [CrossRef] 15. Kubi, H.A.A.; Khan, M.A.; Adhikari, A.; Imran, M.; Kang, S.-M.; Hamayun, M.; Lee, I.-J. Silicon and plant growth-promoting rhizobacteria Pseudomonas psychrotolerans CS51 mitigates salt stress in Zea mays L. Agriculture 2021, 11, 272. [CrossRef] 16. Kazerooni, E.A.; Maharachchikumbura, S.S.N.; Adhikari, A.; Al-Sadi, A.M.; Kang, S.M.; Kim, L.R.; Lee, I.-J. Rhizospheric Bacillus amyloliquefaciens protects Capsicum annuum cv. Geumsugangsan from multiple abiotic stresses via multifarious plant growth-promoting attributes. Front. Plant Sci. 2021, 12, 669693. [CrossRef] Environments 2021, 8, 94 12 of 13 17. Danish, S.; Zafar-ul-Hye, M. Co-application of ACC-deaminase producing PGPR and timber-waste biochar improves pigments formation, growth and yield of wheat under drought stress. Sci. Rep. 2019, 9, 1–13. [CrossRef] 18. Abideen, Z.; Koyro, H.W.; Huchzermeyer, B.; Ansari, R.; Zulfiqar, F.; Gul, B.J.P.B. Ameliorating effects of biochar on photosynthetic efficiency and antioxidant defence of Phragmites karka under drought stress. Plant Biol. 2020, 22, 259–266. [CrossRef] [PubMed] 19. Ren, H.; Lv, C.; Fernández-García, V.; Huang, B.; Yao, J.; Ding, W. Biochar and PGPR amendments influence soil enzyme activities and nutrient concentrations in a eucalyptus seedling plantation. Biomass Convers. Biorefinery 2019, 1–10. [CrossRef] 20. Masciarelli, O.; Llanes, A.; Luna, V. A new PGPR co-inoculated with Bradyrhizobium japonicum enhances soybean nodulation. Microbiol. Res. 2014, 169, 609–615. [CrossRef] 21. Kammann, C.I.; Linsel, S.; Gößling, J.W.; Koyro, H.-W.J.P. Influence of biochar on drought tolerance of Chenopodium quinoa Willd and on soil–plant relations. Plant Soil 2011, 345, 195–210. [CrossRef] 22. Oram, N.J.; van de Voorde, T.F.J.; Ouwehand, G.-J.; Bezemer, T.M.; Mommer, L.; Jeffery, S.; Van Groenigen, J.W.V. Soil amendment with biochar increases the competitive ability of legumes via increased potassium availability. Agric. Ecosyst. Environ. 2014, 191, 92–98. [CrossRef] 23. Jabborova, D.; Wirth, S.; Kannepalli, A.; Narimanov, A.; Desouky, S.; Davranov, K.; Sayyed, R.Z.; El Enshasy, H.; Malek, R.A.; Syed, A.; et al. Co-inoculation of rhizobacteria and biochar application improves growth and nutrientsin soybean and enriches soil nutrients and enzymes. Agronomy 2020, 10, 1142. [CrossRef] 24. Foyer, C.H.; Nguyen, H.; Lam, H.M. Legumes—the art and science of environmentally sustainable agriculture. Plant Cell Environ. 2019, 42, 1–5. [CrossRef] [PubMed] 25. Pampana, S.; Masoni, A.; Arduini, I. Response of cool-season grain legumes to waterlogging at flowering. Can. J. Plant Sci. 2016, 96, 597–603. [CrossRef] 26. Glaeser, J.; Klug, G. Photo-oxidative stress in Rhodobacter sphaeroides: Protective role of carotenoids and expression of selected genes. Microbiology 2005, 151, 1927–1938. [CrossRef] [PubMed] 27. Siebert, C.A.; Qian, P.; Fotiadis, D.; Engel, A.; Hunter, C.N.; Bullough, P.A. Molecular architecture of photosynthetic membranes in Rhodobacter sphaeroides: The role of PufX. EMBO J. 2004, 23, 690–700. [CrossRef] [PubMed] 28. Guo, L.; Zhang, Z.-M.; Lu, D.-T. Effects of Rhodobacter sphaeroides on some physiological-biochemical indexes of wheat seedlings under cadmium stress. J. Agro-Environ. Sci. 2008, 1. 29. Głodowska, M.; Schwinghamer, T.; Husk, B.; Smith, D. Biochar based inoculants improve soybean growth and nodulation. Agric. Sci. 2017, 08, 1048–1064. [CrossRef] 30. Kang, S.-M.; Adhikari, A.; Lee, K.-E.; Khan, M.A.; Shahzad, R.; Dhungana, S.K.; Lee, I.-J. Inoculation with Indole-3-acetic acid-producing rhizospheric Rhodobacter sphaeroides KE149 augments growth of adzuki bean plants under water stress. J. Microbiol. Biotechnol. 2020, 30, 717–725. [CrossRef] 31. Wattoo, F.M.; Rana, R.M.; Fiaz, S.; Zafar, S.A.; Noor, M.A.; Hassan, H.M.; Bhatti, M.H.; Rehman, S.U.; Anis, G.B.; Amir, R.M. Identification of drought tolerant maize genotypes and seedling based morpho-physiological selection indices for crop improvement. Sains Malays. 2018, 47, 295–302. 32. Bhusal, N.; Lee, M.; Lee, H.; Adhikari, A.; Han, A.R.; Han, A.; Kim, H.S. Evaluation of morphological, physiological, and biochemical traits for assessing drought resistance in eleven tree species. Sci. Total Environ. 2021, 779, 146466. [CrossRef] 33. Adhikari, A.; Lee, K.E.; Khan, M.A.; Kang, S.M.; Adhikari, B.; Imran, M.; Jan, R.; Kim, K.M.; Lee, I.J. Effect of silicate and phosphate solubilizing Rhizobacterium Enterobacter ludwigii GAK2 on Oryza sativa L. under cadmium stress. J. Microbiol. Biotechnol. 2020, 30, 118–126. [CrossRef] 34. Adhikari, A.; Khan, M.A.; Lee, K.E.; Kang, S.M.; Dhungana, S.K.; Bhusal, N.; Lee, I.-J. The halotolerant Rhizobacterium— Pseudomonas koreensis MU2 enhances inorganic silicon and phosphorus use efficiency and augments salt stress tolerance in soybean (Glycine max L.). Microorganisms 2020, 8, 1256. [CrossRef] 35. Shahzad, R.; Khan, A.L.; Bilal, S.; Asaf, S.; Lee, I.-J. Plant growth-promoting endophytic bacteria versus pathogenic infections: An example of Bacillus amyloliquefaciens RWL-1 and Fusarium oxysporum f. sp. lycopersici in tomato. Peer J. 2017, 5, e3107. [CrossRef] [PubMed] 36. Adhikari, B.; Dhungana, S.K.; Waqas Ali, M.W.; Adhikari, A.; Kim, I.-D.; Shin, D.-H. Antioxidant activities, polyphenol, flavonoid, and amino acid contents in peanut shell. J. Saudi Soc. Agric. Sci. 2019, 18, 437–442. [CrossRef] 37. Adhikari, B.; Dhungana, S.K.; Ali, M.W.; Adhikari, A.; Kim, I.D.; Shin, D.H. Resveratrol, total phenolic and flavonoid contents, and antioxidant potential of seeds and sprouts of Korean peanuts. Food Sci. Biotechnol. 2018, 27, 1275–1284. [CrossRef] [PubMed] 38. Maheshwari, P.; Assmann, S.M.; Albert, R. A guard cell abscisic acid (ABA) network model that captures the stomatal resting state. Front. Physiol. 2020, 11, 927. [CrossRef] [PubMed] 39. Jacob, T.; Ritchie, S.; Assmann, S.M.; Gilroy, S. Abscisic acid signal transduction in guard cells is mediated by phospholipase D activity. Proc. Natl. Acad. Sci. USA 1999, 96, 12192–12197. [CrossRef] 40. De Ollas, C.; González-Guzmán, M.; Pitarch, Z.; Matus, J.T.; Candela, H.; Rambla, J.L.; Granell, A.; Gómez-Cadenas, A.; Arbona, V. Identification of ABA-mediated genetic and metabolic responses to soil flooding in tomato (Solanum lycopersicum L. mill). Front. Plant Sci. 2021, 12, 613059. [CrossRef] 41. Arbona, V.; Zandalinas, S.I.; Manzi, M.; González-Guzmán, M.; Rodriguez, P.L.; Gómez-Cadenas, A. Depletion of abscisic acid levels in roots of flooded Carrizo citrange (Poncirus trifoliata L. Raf.  Citrus sinensis L. Osb.) plants is a stress-specific response associated to the differential expression of PYR/PYL/RCAR receptors. Plant Mol. Biol. 2017, 93, 623–640. [CrossRef] Environments 2021, 8, 94 13 of 13 42. Shan, C.; Liang, Z. Jasmonic acid regulates ascorbate and glutathione metabolism in Agropyron cristatum leaves under water stress. Plant Sci. 2010, 178, 130–139. [CrossRef] 43. Yosefi, A.; Mozafari, A.; Javadi, T. Jasmonic acid improved in vitro strawberry (Fragaria  ananassa Duch.) resistance to PEG- induced water stress. Plant Cell Tissue Organ Cult. (PCTOC) 2020, 142, 549–558. [CrossRef] 44. Waqas, M.; Shahzad, R.; Hamayun, M.; Asaf, S.; Khan, A.L.; Kang, S.M.; Yun, S.; Kim, K.M.; Lee, I.J. Biochar amendment changes jasmonic acid levels in two rice varieties and alters their resistance to herbivory. PLoS ONE 2018, 13, e0191296. [CrossRef] [PubMed] 45. Zhang, S.; Moyne, A.-L.; Reddy, M.S.; Kloepper, J.W. The role of salicylic acid in induced systemic resistance elicited by plant growth-promoting rhizobacteria against blue mold of tobacco. Biol. Control. 2002, 25, 288–296. [CrossRef] 46. De Vleesschauwer, D.; Djavaheri, M.; Bakker, P.A.; Höfte, M. Pseudomonas fluorescens WCS374r-induced systemic resistance in rice against Magnaporthe oryzae is based on pseudobactin-mediated priming for a salicylic acid-repressible multifaceted defense response. Plant Physiol. 2008, 148, 1996–2012. [CrossRef] [PubMed] 47. Hayat, S.; Hasan, S.A.; Fariduddin, Q.; Ahmad, A.J. Growth of tomato (Lycopersicon esculentum) in response to salicylic acid under water stress. J. Plant Interact. 2008, 3, 297–304. [CrossRef] 48. Singh, B.; Usha, K. Salicylic acid induced physiological and biochemical changes in wheat seedlings under water stress. Plant Growth Regul. 2003, 39, 137–141. [CrossRef] 49. Yang, Y.; Qi, M.; Mei, C. Endogenous salicylic acid protects rice plants from oxidative damage caused by aging as well as biotic and abiotic stress. Plant J. Cell Mol. Biol. 2004, 40, 909–919. [CrossRef] [PubMed] 50. Sakhabutdinova, A.; Fatkhutdinova, D.; Bezrukova, M.; Shakirova, F. Salicylic acid prevents the damaging action of stress factors on wheat plants. Bulg. J. Plant Physiol. 2003, 21, 314–319. 51. Liu, Z.; Ding, Y.; Wang, F.; Ye, Y.; Zhu, C.J. Role of salicylic acid in resistance to cadmium stress in plants. Plant Cell Rep. 2016, 35, 719–731. [CrossRef] 52. Waqas, M.; Khan, A.L.; Kamran, M.; Hamayun, M.; Kang, S.M.; Kim, Y.H.; Lee, I.-J. Endophytic fungi produce gibberellins and indoleacetic acid and promotes host-plant growth during stress. Molecules 2012, 17, 10754–10773. [CrossRef] 53. Li, Z.; Yong, B.; Cheng, B.; Wu, X.; Zhang, Y.; Zhang, X.; Peng, Y.J. Nitric oxide, -aminobutyric acid, and mannose pretreatment influence metabolic profiles in white clover under water stress. J. Integr. Plant Biol. 2019, 61, 1255–1273. [CrossRef] [PubMed] 54. Farhangi-Abriz, S.; Faegi-Analou, R.; Nikpour-Rashidabad, N.J. Polyamines, affected the nitrogen partitioning, protein accumula- tion and amino acid composition of mung bean under water stress. J. Crop. Sci. Biotechnol. 2017, 20, 279–285. [CrossRef] 55. Vwioko, E.; Adinkwu, O.; El-Esawi, M.A. Comparative physiological, biochemical, and genetic responses to prolonged waterlog- ging stress in okra and maize given exogenous ethylene priming. Front. Physiol. 2017, 8, 632. [CrossRef] [PubMed] 56. Kim, Y.; Seo, C.W.; Khan, A.L.; Mun, B.G.; Shahzad, R.; Ko, J.W.; Yun, B.W.; Park, S.K.; Lee, I.J. exo-ethylene application mitigates waterlogging stress in soybean (Glycine max L.). BMC Plant Biol. 2018, 18, 254. [CrossRef] 57. Haddadi, B.S.; Hassanpour, H.; Niknam, V. Effect of salinity and waterlogging on growth, anatomical and antioxidative responses in Mentha aquatica L. Acta Physiol. Plant. 2016, 38, 119. [CrossRef] 58. Ksouri, R.; Megdiche, W.; Debez, A.; Falleh, H.; Grignon, C.; Abdelly, C. Salinity effects on polyphenol content and antioxidant activities in leaves of the halophyte Cakile maritima. Plant Physiol. Biochem. 2007, 45, 244–249. [CrossRef] 59. Giorgi, A.; Mingozzi, M.; Madeo, M.; Speranza, G.; Cocucci, M. Effect of nitrogen starvation on the phenolic metabolism and antioxidant properties of yarrow (Achillea collina Becker ex Rchb.). Food Chem. 2009, 114, 204–211. [CrossRef]

Journal

Environments – Multidisciplinary Digital Publishing Institute

Published: Sep 15, 2021

Keywords: biochar; soybean; Rhodobacter sphaeroides KE149; waterlogging; abiotic stress

There are no references for this article.