Hydrogen sulfide - cysteine cycle system enhances cadmium tolerance through alleviating cadmium-induced oxidative stress and ion toxicity in Arabidopsis roots.

Cadmium (Cd) is a common toxic heavy metal ion. We investigated the roles of hydrogen sulfide (HS) and cysteine (Cys) in plant responses to Cd stress. The expression of HS synthetic genes LCD and DES1 were induced by Cd within 3 h, and endogenous HS was then rapidly released. HS promoted the expression of Cys synthesis-related genes SAT1 and OASA1, which led to endogenous Cys accumulation. The HS and Cys cycle system was stimulated by Cd stress, and it maintained high levels in plant cells. HS inhibited the ROS burst by inducing alternative respiration capacity (AP) and antioxidase activity. HS weakened Cd toxicity by inducing the metallothionein (MTs) genes expression. Cys promoted GSH accumulation and inhibited the ROS burst, and GSH induced the expression of phytochelatin (PCs) genes, counteracting Cd toxicity. In summary, the HS and Cys cycle system played a key role in plant responses to Cd stress. The Cd tolerance was weakened when the cycle system was blocked in lcddes1-1 and oasa1 mutants. This paper is the first to describe the role of the HS and Cys cycle system in Cd stress and to explore the relevant and specificity mechanisms of HS and Cys in mediating Cd stress.