Boron-induced phenylpropanoid metabolism, Na+/K+ homeostasis and antioxidant defense mechanisms in salt-stressed soybean seedlings

Boron (B)-induced alleviation of salt stress in plants have been examined in some details, but the mechanisms underlying these processes remain largely unexplored. In this study, soybean seedlings were irrigated with nutrient solution containing either 0 or 100 mM NaCl with two B levels. The results showed that salt stress adversely inhibited plant growth-related parameters and photosynthetic rate, caused oxidative damage in terms of higher malondialdehyde (MDA) and reactive oxygen species (ROS) levels. Co-treatment with B and salt causes a decrease in overall Na⁺ content in plant, with increased in Na⁺ content in root and root cell wall (CW) and a reduction in Na⁺ translocation factor. Additionally, B supplementation boosted antioxidant enzyme activities, and reduced MDA, H₂O₂, and osmotic substance levels under salt stress. Boron specifically induced the phenylpropanoid metabolism pathway, enhanced the antioxidants accumulation such as cinnamic acid, coumarin, and sinapic acid, as well as flavonoids like glycine and genistein, collectively reduced salt-induced ROS accumulation. Taken together, B mitigates salt stress by enhancing root antioxidant defenses and activating the phenylpropanoid metabolism pathway which reduces ROS level. Boron enhanced root retention of Na⁺ to alleviate oxidative damage caused by Na⁺ accumulation in leaf, ultimately improves photosynthesis and promotes seedlings growth.