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.
