Insight into the Mechanism of Salt-Induced Oxidative Stress Tolerance in Soybean by the Application of Bacillus subtilis: Coordinated Actions of Osmoregulation, Ion Homeostasis, Antioxidant Defense, and Methylglyoxal Detoxification

Abstract

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 a presoaking with seeds or a direct application with pot soil. After 20 days of sowing, both the seed- and soil-inoculated plants were exposed to 50, 100, and 150 mM of 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, the plant growth, biomass accumulation, water relations, and content of the photosynthetic pigments were decreased. Salt stress also caused an increased Na+/K+ ratio and decreased Ca2+. On the contrary, the B. subtilis inoculated plants showed increased levels of AsA and GSH, their redox balance, and the activities of the AsA–GSH pathway enzymes, superoxide dismutase, catalase, glutathione peroxidase, glutathione S-transferase, and peroxidase. The 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 Ca2+ was increased to maintain the ion homeostasis in the B. subtilis inoculated plants under salinity. Furthermore, the 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 systems along with maintaining ion homeostasis and osmotic adjustments. In addition, it was evident that the soil inoculation performed better than the seed inoculation in mitigating salt-induced oxidative damages in soybean.

Biological control potential of worrisome wheat blast disease by the seed endophytic bacilli

“…Under biotic and abiotic stress, various reactive oxygen species (ROS) are produced in plant cells and are scavenged or detoxified by various antioxidant enzymes and metabolites. Hasanuzzaman et al (2022) showed that applying B. subtilis can induce coordinated actions of osmoregulation, ion homeostasis, and antioxidant defense in host plants. The presence of these antioxidant enzyme-related gene clusters in our bacterial isolates may indicate that they are involved in ROS metabolism during blast infection.…”

Probiotic <em>Bacillus</em> Species: Promising Biological Control Agents for Managing Worrisome Wheat Blast Disease

“…Under biotic and abiotic stress, various reactive oxygen species (ROS) are produced in plant cells and scavenged or detoxified by various antioxidant enzymes and metabolites. Hasanuzzaman et al [65] described coordinated actions of osmoregulation, ion homeostasis, and antioxidant defense induced in host plants by the application of B. subtilis. The antioxidant enzyme-related gene clusters present in our biocontrol bacteria may be involved in ROS metabolism during blast infection.…”

Recent advances in PGPR-mediated resilience toward interactive effects of drought and salt stress in plants

“…After the plants absorb salt, the sodium ions (Na + ) are transported to the plant’s shoots via the xylem, eventually accumulating in the leaves and shoots ( Ullah et al, 2021 ). The consensus is that sodium ion buildup in plants is harmful because it competes for binding sites with potassium ions (K + ) essential for cellular activity ( Desoky et al, 2020 ; Hasanuzzaman et al, 2022 ). Similarly, ROS are developed within the plants that can subsequently induce lipid peroxidation in plant cell membranes, lead to electrolyte leakage from plant cells, and either augment photorespiration or reduce the transpiration ensuing in a slower photosynthesis rate, thereby having a detrimental effect on the production and quality of the plants ( Khan, 2022 ).…”

“…Due to the imbalanced gas exchange and decreased leaf area, photosynthesis slows down, and therefore, to mitigate the effect of these stressors on plants, they should sustain water homeostasis and maintain their photosynthetic structures unharmed. Further, the osmotic stress brought on by salt and drought directly impacts numerous soil processes, including stressing out the microorganisms ( Hasanuzzaman et al, 2022 ). When under stressful conditions, the soil bacteria adjust their osmotic conditions and sustain themselves hydrated by cellular compatible solute accumulation that assists in maintaining the right amount of water in their cells ( Desoky et al, 2020 ).…”