Hydrogen sulfide decreases Cd translocation from root to shoot through increasing Cd accumulation in cell wall and decreasing Cd2+ influx in Isatis indigotica

Hydrogen sulfide (H2S), a small gaseous signalling molecule, plays a pivotal role in the plant response to heavy metal stress. Here, we revealed a novel mechanism of Isatis indigotica resistance to cadmium (Cd) stress, in which H2S promotes Cd accumulation in the root and decreases the long-distance transport of Cd from the root to shoot. Cd significantly inhibited Isatis indigotica growth and induced the endogenous H2S level. Application of NaHS (a H2S donor) alleviated the effects of Cd. NaHS restriction of the translocation factor of Cd, elevated the Cd content in roots and depressed the Cd content in shoots. Cd stress decreased the cellulose and pectin contents in the cell wall, but NaHS restored the effect of Cd on the cell wall components. The Cd2+ fluxes were detected by noninvasive microtest technology (NMT). The data showed that NaHS pretreatment decreased the Cd2+ influx and proportion of the Cd content in organelles. We analyzed the effect of NaHS on the metallothionein and phytochelatin (PC) contents in roots and found that the PC and metallothionein1A (MT1A) contents were induced by NaHS. Additionally, the chemical forms of Cd2+ were changed by NaHS. Thus, H2S alters the content of cell wall component, improves Cd accumulation in the cell wall, depresses Cd2+ transmembrane movement, induces the synthesis of metallothioneins and decreases the toxicity of intracellular Cd. Our finding has great value to reduce the loss of Isatis indigotica resulted by heavy metals stress.