Hydrogen Sulfide Is Involved In Cysteine- Induced Alleviation Of Primary Root Growth Inhibition And Oxidative Damage Due To Cadmium Stress In Arabidopsis

Cysteine is an important protein in plants. The integration of reduced sulphur into cysteine is a central step in the assimilation of inorganic sulphur. Cysteine functions as a precursor for antioxidants and many defense compounds, as well as vitamins and cofactors. cysteine is found to alleviate heavy metal stresses through GSH synthesis. Besides, cysteine can be catalyzed by cysteine desulfhydrase to form H2S, ammonia and pyruvate. This is the essential source of endogenous H2S in plants. As one of important gaseous messenger molecules, H2S participates in plant systems in controlling root growth and development, and modulates many adaptive responses to different biotic and abiotic stresses. As an important source of endogenous H2S, can cysteine alleviate cadmium stress by generating H2S? we examined the question above, and the main results were summarized as follows:Cadmium stress induced the synthesis of endogenous cysteine and H2S in Arabidopsis seedling roots, and the producing time of H2S is later than that of cysteine; cadmium stress also induced the expression of cysteine metabolism associated genes, among which the expression of L-CDes (the gene of L-cysteine desulfhydrase) and D-CDes (the gene of D-cysteine desulfhydrase) increased mostly. Furthermore, the addition of cysteine desulfhydrase inhibitor, DL-propargylglycine (PAG), potentiated the PR growth inhibition by cadmium exposure. Both pretreatments of cysteine and H2S donor sodium hydrosulfide (NaHS), instead of two other cysteine desulfuration products pyruvate and ammonia, reversed the inhibition effect of cadmium on primary root (PR) elongation.Furthermore, the investigation of H2S synthesizing mutants 1-cdes and d-cdes demonstrated that compared with the wild type, 1-cdes displayed the highest sensitivity, and that of d-cdes was next; simultaneously, the accumulation of H2S content in 1-cdes and d-cdes induced by cadmium exposure was significantly weakened. Further analyse of lipid peroxidation and loss of membrane integrity in seedling roots using histochemical staining demonstrated that 1-cdes and d-cdes were more sensitive to cadmium exposure. Pretreatment of NaHS effectively alleviated lipid peroxidation and loss of membrane integrity in wild type and both mutants, while the alleviation effect of cysteine was only significant in wild type. Besides, cadmium exposure significantly induced the expression of antioxidative genes of CAT1?CAT2?APX1?APX2 in wild type, which is stronger than that in l-cdes and d-cdes.Taking together, our observation indicates that H2S may be involved in cysteine-induced alleviation of PR growth inhibition and oxidative damage in Arabidopsis due to cadmium stress.