Oxidative Damage in Roots of Rice (Oryza sativa L.) Seedlings Exposed to Microplastics or Combined with Cadmium

This study aimed to investigate the effect of 10-40 mg L^-1 polystyrene microplastics (PS-MPs), 0.05 mg L^-1 cadmium (Cd) and their combination on the growth and related physiological and toxicological responses in Oryza sativa L. seedling roots. Results showed that the fresh weight, dry weight and root lengths of treatments by PS-MPs, Cd single and combinative were all lower than the control, and opposite phenomenon appeared in production of superoxide radical (O₂^-.), malondialdehyde (MDA) and carbonylated protein. Superoxide dismutase (SOD) and guaiacol peroxidase (POD) activities induced by 10-40 mg L^-1 PS-MPs and combination with Cd were almost higher than those by Cd alone, expression of heat shock protein (HSP)70 and carbonylated protein slightly decreased. In compound exposure, 10-20 mg L^-1 PS-MPs alleviated Cd damage and promoted root growth by increasing SOD and POD activities, but 40 mg L^-1 PS-MPs accelerated the accumulation of Cd, MDA, and O₂^-., which was responsible for decreasing root biomass and the aggravating necrosis of root tip cells.