Physiological and biochemical responses of pepper (Capsicum annuum) to cadmium stress: The mitigating effects of exogenous abscisic acid.

The production of pepper is increasingly challenged by cadmium (Cd) contamination. Abscisic acid (ABA) is supposed to alleviate Cd-induced toxicity and reduce the accumulation of Cd. However, the underlying physiological mechanisms by which ABA regulates Cd tolerance remain unclear. Therefore, this study investigates the mitigation of Cd toxicity in pepper exposed to Cd stress through the application of exogenous ABA under hydroponic conditions. The analysis focused on the subcellular distribution of Cd in the root, its localization in cell wall polysaccharide components, and the associated physiological indices. The results showed that ABA treatment significantly reduced Cd accumulation in pepper roots and shoots, which suggests that ABA effectively decreases Cd translocation from roots to aboveground tissues. This was accompanied by enhanced antioxidant activity, as evidenced by increased peroxidase and catalase activities. Furthermore, ABA regulated the subcellular distribution of Cd in root tissues, decreased Cd content in the cell wall and thereby mitigating Cd toxicity at the cellular level. The addition of ABA also reduced the content of hydrogen peroxide and malondialdehyde, indicating a reduction in lipid peroxidation and cell membrane damage. These findings highlight that ABA can enhance plant tolerance to Cd stress by modifying Cd distribution within the plant, boosting the antioxidant defense mechanism, and altering cell wall composition to limit Cd absorption. This study suggests that exogenous ABA could be a potential strategy for improving Cd resistance in pepper and reducing Cd contamination in crops.