Iminodisuccinic Acid Relieved Cadmium Stress in Rapeseed Leaf by Affecting Cadmium Distribution and Cadmium Chelation with Pectin

Rapeseed (Brassica napus L.) is a nutritious vegetable, while cadmium (Cd) pollution threatens the growth, productivity, and food security of rapeseed. By studying the effects of iminodisuccinic acid (IDS), an easily biodegradable and environmental friendly chelating agent, on Cd distribution at the organ and cellular level, we found IDS promoted dry matter accumulation of rapeseed and increased the contents of photosynthetic pigment in leaves. Inhibited root-shoot Cd transport resulted in higher activity of antioxidant enzymes and decreased hydrogen peroxide (H2O2) and malondialdehyde (MDA) accumulation in leaves, which indicated that IDS contributed to alleviating Cd-caused oxidative damage in leaf cells. Additionally, IDS increased Cd subcellular distribution in cell wall (CW), especially in covalently bound pectin (CSP), and relieved Cd toxicity in organelle of leaves. IDS also enhanced demethylation of CSP. The Cd content in CSP, demethylation degree, and pectin methylesterase activity of CSP increased by 37.95%, 13.34%, and 13.16%, respectively, while IDS did not change the contents of different CW components. The improved Cd fixation in leaf CW was mainly attributed to enhance demethylation of covalently bound pectin (CSP) and Cd chelation with CSP.