Ethylene and hydrogen sulfide regulate hexavalent chromium toxicity in two pulse crops: Implication on growth, photosynthetic activity, oxidative stress and ascorbate glutathione cycle.

Sustainable agriculture has become prime importance to feed growing population. To achieve this goal application of exogenous hormones and signaling molecules are gaining important. In this context, we have investigated potential of ethylene (25 μM ethephon; donor) and HS (10 μM NaHS; donor) in mitigating hexavalent chromium [Cr (VI), 50 μM] toxicity in two pulse seedlings: black bean and mung bean. Cr(VI) declined growth and gas exchange parameters (photosynthetic rate, stomatal conductance, sub cellular CO concentration, and transpiration level) which was accompanied by intracellular accumulation of Cr in both pulse crops and the damaging effect was greater in mung bean seedlings. The suppression in the growth and related parameters was occurred due to higher buildup of oxidative stress markers; O‾, HO, lipid peroxidation (as malondialdehyde, MDA equivalents) and membrane injury in leaf and root of both pulse crops. Cr induced disturbance in AsA-GSH cycle (reduction in the activity of glutathione reductase, ascorbate peroxidase, monodehydroascorbate reductase and dehydroascorbate reductase, and the amount of ASA and GSH) could be one of the reasons for greater accumulation of HO. Further, exogenous application of ethylene and HS significantly ameliorated Cr toxicity on growth and photosynthetic activity by significantly lowering the intracellular Cr accumulation and oxidative biomarkers, and also by strengthening the activity of AsA-GSH cycle. The exogenous application of biosynthesis inhibitors of ethylene (AVG) and HS (PAG) caused greater damaging effect on these parameters due to more accumulation of Cr(VI), thereby suggesting that the endogenous levels of these regulators are critical for Cr(VI) tolerance. Interestingly, ET did not rescue adverse effects of Cr(VI) in absence of endogenous HS, while HS could do so even without endogenous ethylene, suggesting that HS played downstream signaling to ethylene in regulating Cr(VI) toxicity. Hence, being cheap and easily available theses growth regulators may be considered for sustainable agriculture.