Sodium Hydrosulfide Mitigates Cadmium Toxicity by Promoting Cadmium Retention and Inhibiting Its Translocation from Roots to Shoots in Brassica napus

The association between hydrogen sulfide (H2S) and cell wall composition with regard to the mitigation of cadmium (Cd) toxicity in Brassica napus L. was investigated. Cd caused growth retardation, leaf chlorosis, and decreased endogenous H2S content in Brassica napus roots. Stimulating L-cysteine desulfhydrase (LCD)-mediated H2S production with H2S releaser (NaHS) markedly improved plant growth, reduced Cd content in stems and leaves, and rescued Cd-induced chlorosis. Furthermore, increased Cd retention was observed in root cell walls, indicating that NaHS reduced Cd movement from the roots to upper-plant parts. Exogenous NaHS also significantly increased the content of pectin and the activity of pectin methylesterase in cell walls of roots, thereby increasing Cd retention in pectin fractions. However, intensification of H2S barely affected hemicellulose content under Cd stress. Intensified H2S signal, therefore, alleviates Cd toxicity in Brassica napus by increasing pectin content and its demethylation, increasing Cd fixation in cell walls, and reducing root-to-shoot Cd translocation.