Gibberellic acid-induced generation of hydrogen sulfide alleviates boron toxicity in tomato (Solanum lycopersicum L.) plants.

It was aimed to examine the role of gibberellic acid (GA) induced production of hydrogen sulfide (H2S) in alleviating boron toxicity (BT) in tomato plants. Two weeks after germination, a solution consisting of GA (100 mg L-1) was sprayed once a week for 14 days to the leaves of cv. "SC 2121" of tomato under BT stress (BT; 2.0 mM). Before starting BT treatment, half of the seedlings were retained in a solution containing a scavenger of H2S, 0.1 mM hypotaurine (HT), for 12 h. Boron toxicity led to a substantial decrease in dry biomass, leaf water potential, leaf relative water content, chlorophyll a, chlorophyll b, photosynthetic quantum yield (Fv/Fm), ascorbate (AsA) and glutathione (GSH) in the tomato plants. However, it increased the accumulation of hydrogen peroxide (H2O2), malondialdehyde (MDA), endogenous hydrogen sulfide (H2S), and free proline as well as the activities of catalase, superoxide dismutase and peroxidase. The supplementation of GA mitigated BT by increasing the endogenous H2S, and leaf Ca2+ and K+, and reducing the contents of leaf H2O2, MDA, and B as well as membrane leakage. GA-induced BT tolerance was further enhanced by the supplementation of sodium hydrosulfide (0.2 mM NaHS), an H2S donor. A scavenger of H2S, hypotaurine (0.1 mM HT) was supplied along with the GA and NaHS treatments to assess if H2S was involved in GA-induced BT tolerance of tomato plants. Addition of HT reversed the beneficial effect of GA on oxidative stress and antioxidant defence system by reducing the endogenous H2S without changing L-DES activity, suggesting that H2S participates in GA-induced tolerance to BT of tomato plants.