Exogenous Melatonin Attenuates Cd Toxicity in Tea (Camellia sinensis)

Abstract

Cadmium (Cd) is highly toxic and not easily degradable. It damages plant growth and results in large-scale economic losses. The present study explored the feasibility of using melatonin to alleviate Cd toxicity, and to reduce Cd accumulation in tea seedlings cultivated in Cd-contaminated soil. Exogenous melatonin, especially at 150 μM, promoted tea seedling growth under Cd stress, and increased the photosynthetic pigment by 16% and soluble protein content by 5%. Furthermore, melatonin effectively increased the activities of superoxide dismutase (SOD), and peroxidase (POD) by 21 and 31%, respectively, contributed to a decrease of the malondialdehyde (MDA) by 2% and the Cd content in leaves by 52%. Furthermore, soil enzyme activities were enhanced, including acid phosphatase (ACP), urease (UE), soil sucrase (SC), and soil catalase (CAT), by 11, 70, 1, and 18%, respectively, along with a pH reduction and available Cd content increase, after melatonin application. Taken together, our results provide evidence that melatonin lessens the adverse Cd effects on tea seedlings’ physiology, mainly through enhancing the antioxidant capacity of the plants and soils to scavenge reactive oxygen species (ROS) upon Cd exposure. Therefore, melatonin may be used as a modulator to alleviate Cd-induced toxicity in tea seedlings, thereby resulting in healthier tea plant growth.