Interactive effects of drought and cadmium stress on adzuki bean seedling growth, DNA damage repair, and Cd accumulation

Cadmium (Cd) is one of the most toxic heavy metal pollutants that seriously affects crop survival and human health. Drought is a common abiotic stress that affects crop production and yield. However, appropriate drought treatment can be used as a tillage measure to reduce the growth inhibition and toxic accumulation of Cd in plants. In this study, Adzuki bean (Vigna angularis L., cultivar Pearl red) seedlings were hydroponically grown to investigate the effects of Cd (2.5 mg & sdot;L-1 CdCl2), drought (D, 5 % (W/V) PEG6000), and combined stress of Cd and drought (Cd+D) on the plant growth. Compared with the control group, Cd, D, and Cd+D stress significantly inhibited the growth of adzuki bean seedling plants, among which Cd+D stress had the highest degree of inhibition. Compared with Cd stress, Cd+D treatment significantly up-regulated the expression levels of Cd ion transport-related genes in adzuki bean seedling roots, resulting in a decrease in Cd accumulation. In addition, Cd+D treatment significantly increased the activities of superoxide dismutase (SOD) and ascorbate peroxidase (APX), but significantly decreased the activities of peroxidase (POD) and catalase (CAT) enzymes, which led to a decrease in superoxide anion (O-2(-) ) content and an increase in hydrogen peroxide (H2O2) content in seedling roots. Compared with Cd stress, Cd+D treatment slowed down the G1/S phase of root cells; however, promoted the G2/ M phase. Although Cd+D treatment up-regulated the expression levels of DNA damage repair genes in the roots of adzuki bean seedlings under Cd stress, but not significantly reduce the degree of DNA damage, which may due to the existence of a DNA damage tolerance mechanism. This may also be the main reason for the inhibition of the adzuki bean growth.