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

Cadmium (Cd 2+ ) is a common toxic heavy metal ion. We investigated the roles of hydrogen sulfide (H 2 S) and cysteine (Cys) in plant responses to Cd 2+ stress. The expression of H 2 S synthetic genes LCD and DES1 were induced by Cd 2+ within 3 h, and endogenous H 2 S was then rapidly released. H 2 S promoted the expression of Cys synthesis-related genes SAT1 and OASA1 , which led to endogenous Cys accumulation. The H 2 S and Cys cycle system was stimulated by Cd 2+ stress, and it maintained high levels in plant cells. H 2 S inhibited the ROS burst by inducing alternative respiration capacity (AP) and antioxidase activity. H 2 S weakened Cd 2+ 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 2+ toxicity. In summary, the H 2 S and Cys cycle system played a key role in plant responses to Cd 2+ stress. The Cd 2+ 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 H 2 S and Cys cycle system in Cd 2+ stress and to explore the relevant and specificity mechanisms of H 2 S and Cys in mediating Cd 2+ stress.