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 (H 2 S), 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 H 2 S significantly alleviated Cd-induced growth inhibition and reductions in chlorophyll content, and dramatically depressed leaf malondialdehyde (MDA) accumulation. Addition of H 2 S markedly reduced Cd concentration in plants and increased leaf soluble protein contents compared with the corresponding Cd-only treatments. Supplemental H 2 S 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 (H 2 O 2 ) and superoxide ions (O 2 ⋅− ) 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 H 2 S 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 H 2 S is involved in the reduced Cd uptake/translocation and decreased MDA, H 2 O 2 and O 2 ⋅− accumulation, and increased chlorophyll.