Interpretation of melatonin-mediated vacuolar compartmentalization at the cellular level in the hyperaccumulator plant Solanum nigrum L. under cadmium stress

Abstract Melatonin can alleviate cadmium (Cd) stress in plants, but the cellular-level mechanism remains unclear, particularly in relation to its impact on detoxification processes within the protoplast and vacuole of plants. The plant Solanum nigrum L. was selected to explore the Cd concentration on vacuolar compartmentalization in the leaf cell under the application of exogenous melatonin. The contents of total Cd, Cd²⁺, ascorbic acid-glutathione (AsA-GSH) and reactive oxygen species (ROS) were determined in protoplasts and vacuoles of leaf cells through subcellular separation. It was found that vacuolar compartmentalization is a dynamic strategy accompanied by the reasonable allocation and continuous consumption of related substances outside the vacuole. Melatonin promoted a more reasonable allocation of resources outside the vacuole to maintain homeostasis. These findings might have implications for understanding melatonin-mediated cellular tolerance mechanisms and instructing the genetic ways to devise more ideal hyperaccumulator plants.