Glutathione and hydrogen sulfide are required for sulfur-mediated mitigation of Cr(VI) toxicity in tomato, pea and brinjal seedlings.

In plants, investigation on heavy metal toxicity and its mitigation by nutrient elements have gained much attention. However, mechanism(s) associated with nutrients-mediated mitigation of metal toxicity remain elusive. In this study, we have investigated the role and interrelation of glutathione (GSH) and hydrogen sulfide (H ₂ S) in the regulation of hexavalent chromium [Cr(VI)] toxicity in tomato (Solanum lycopersicum), pea (Pisum sativum) and brinjal (Solanum melongena) seedlings, supplemented with additional sulfur (S). The results show that Cr(VI) significantly reduced growth, total chlorophyll and photosynthetic quantum yield of tomato, pea and brinjal seedlings which was accompanied by enhanced intracellular accumulation of Cr(VI) in roots. Moreover, Cr(VI) enhanced the generation of reactive oxygen species in the studied vegetables, while antioxidant defense system exhibited differential responses. However, additional supply of S alleviated Cr(VI) toxicity. Interestingly, addition of l-buthionine sulfoximine (BSO, a glutathione biosynthesis inhibitor) further increased Cr(VI) toxicity even in the presence of additional S but GSH addition reverses the effect of BSO. Under similar condition, endogenous H ₂ S, l-cysteine desulfhydrase (DES) activity and cysteine content did not significantly differ when compared to controls. Hydroxylamine (HA, an inhibitor of DES) also increased Cr(VI) toxicity even in the presence of additional S but sodium hydrosulfide (NaHS, an H ₂ S donor) reverses the effect of HA. Moreover, Cr(VI) toxicity amelioration by NaHS was reversed by the addition of hypotaurine (HT, an H ₂ S scavenger). Taken together, the results show that GSH which might be derived from supplied S is involved in the mitigation of Cr(VI) toxicity in which H ₂ S signaling preceded GSH biosynthesis.
(© 2019 Scandinavian Plant Physiology Society.)