Exogenous hydrogen sulfide reduces cadmium uptake and alleviates cadmium toxicity in barley

Greenhouse hydroponic experiments were conducted to evaluate the ameliorative effects of NaHS, a donor of hydrogen sulfide (H2S), on different levels of cadmium (Cd) stress in barley seedlings. The results showed that Cd stress dramatically reduced plant biomass, chlorophyll and soluble protein contents. Exogenous application of H2S significantly alleviated Cd-induced growth inhibition and reductions in chlorophyll content, and dramatically depressed leaf malondialdehyde (MDA) accumulation. Addition of H2S markedly reduced Cd concentration in plants and increased leaf soluble protein contents compared with the corresponding Cd-only treatments. Supplemental H2S counteracted Cd-induced alterations of certain antioxidant enzymes, e.g. elevated depressed superoxide dismutase in leaves and roots and depressed Cd-induced increase in leaf catalase and ascorbate peroxidase activities. Pretreatment with 200 μM NaHS markedly reduced the accumulation of hydrogen peroxide (H2O2) and superoxide ions (O2⋅−) in roots tissues treated with 5 and 25 μM Cd, which was consistent with the result of histochemical staining of roots. Compared with non-pretreated plants, exogenous H2S significantly increased reduced glutathione contents and ascorbate contents in barley given the 25 μM Cd treatment. These results indicate that the mitigated Cd toxicity by H2S is involved in the reduced Cd uptake/translocation and decreased MDA, H2O2 and O2⋅− accumulation, and increased chlorophyll.