MITIGATION OF SALT STRESS IN SOYBEAN BY THE APPLICATION OF Bacillus SPECIES

Abstract

Executive Summary Considering the growth-promoting potential and other regulatory roles of bacteria, we investigated the possible mechanism of the role of Bacillus subtilis in conferring salt tolerance in soybean. Soybean (Glycine max cv. BARI Soybean-5) seeds were inoculated with B. subtilis, either through presoaking with seeds or direct application with pot soil. After 20 days of sowing, both seed- and soil-inoculated plants were exposed to 50, 100, and 150 mM NaCl for 30 days. A clear sign of oxidative stress was evident through a remarkable increase in lipid peroxidation, hydrogen peroxide, methylglyoxal, and electrolyte leakage in the salt-treated plants. Moreover, the efficiency of the ascorbate (AsA)-glutathione (GSH) pathways was declined. Consequently, plant growth, biomass accumulation, water relations, and synthesis of the photosynthetic pigments were decreased. Salt stress also caused increased Na + /K + ratio and decreased Ca

26 2+ . On the contrary, B. subtilis inoculated plants showed increased levels of AsA and GSH, their redox balance, and the activities of AsAGSH

pathway enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, and peroxidase. B. subtilis inoculated plants also enhanced the activities of glyoxalase enzymes, which mitigated methylglyoxal toxicity in coordination with ROS homeostasis. Besides this, the accumulation of K + and Ca 2+ was increased to maintain the ion homeostasis in the B. subtilis inoculated plants under salinity. Furthermore, plant water status was uplifted in the salt-treated soybean plants with B. subtilis inoculation. This investigation reveals the potential of B. subtilis in mitigating salt-induced oxidative stress in soybean plants through modulating the antioxidant defense and glyoxalase system along with maintaining ion homeostasis and osmotic adjustments.