Dopamine improves the phytoremediation capacity of hyperaccumulator <i>Solanum nigrum</i> var. <i>humile</i> for cadmium

Dopamine can alleviate cadmium (Cd) stress in plants and promote plant growth but has differential regulatory effects on Cd accumulation among different plant species. To enhance the phytoremediation capacity of hyperaccumulators, the effects of dopamine on the Cd accumulation in hyperaccumulator Solanum nigrum var. humile were investigated using a pot experiment. The Cd treatment (5 mg/L) induced stress, inhibiting the growth of S. nigrum var. humile by reducing biomass, photosynthetic pigment content, and photosynthetic gas exchange parameters, while increasing antioxidant enzyme activity. Under Cd stress, dopamine treatment (100 μmol/L) increased the root length, tolerance coefficient, and biomass of S. nigrum var. humile, without significantly affecting plant height or root/shoot ratio. Compared to Cd treatment, the root and shoot biomass treated with dopamine treatment increased by 18.97% and 11.57%, respectively. Additionally, dopamine treatment enhanced photosynthetic pigment content, photosynthetic gas exchange parameters, antioxidant enzyme activities, Cd content, and Cd accumulation amount of S. nigrum var. humile. Relative to Cd treatment, the chlorophyll a content, chlorophyll b content, carotenoid content, root Cd content, shoot Cd content, and whole plant Cd accumulation amount treated with dopamine treatment increased by 34.00%, 41.01%, 10.92%, 23.16%, 12.36%, and 35.64%, respectively. Furthermore, correlation and grey relational analyses revealed that root Cd content, superoxide dismutase activity, peroxidase activity, and catalase activity were closely correlated with shoot Cd content. Therefore, dopamine can promote Cd uptake and enhance the phytoremediation capacity of S. nigrum var. humile.