Ethylene needs endogenous hydrogen sulfide for alleviating hexavalent chromium stress in Vigna mungo L. and Vigna radiata L.

Chromium toxicity to crops is a big scientific issue of the present time. Thus, continuous scientific attempts have been taken for reducing chromium toxicity in crop plants. In this study, we have tested potential of ethylene (ET) and hydrogen sulfide (H2S) in alleviating hexavalent chromium [(Cr(VI)] stress in two pulse crops i.e. black bean and mung bean. Cr(VI) declined growth (by 21 % and 27 % in black and mung bean, respectively) and also negatively affected photosynthesis in both pulse crops due to accumulation of Cr(VI) and cell death in roots. Under similar conditions, levels of reactive oxygen species (ROS) were enhanced but antioxidant defense system showed differential responses. The addition of AVG (an inhibitor of ethylene biosynthesis) and PAG (an inhibitor of H2S biosynthesis) with Cr(VI) further increased toxicity of Cr(VI) suggesting that endogenous H2S and ET are important for tolerating Cr(VI) toxicity. But supplementation of either ET or H2S alleviated Cr(VI) toxicity. Interestingly, ET did not rescue negative effects of PAG under Cr(VI) stress but NaHS rescued negative effect of AVG. Overall, results indicate that though both ET and H2S are able in alleviating Cr(VI) stress but endogenous H2S is crucial in ET-mediated mitigation of Cr(VI) stress. Furthermore, H2S appears to be a downstream signal of ET in alleviating Cr(VI) stress in two pulse crops.