Abscisic Acid Improves the Ability of Accumulator Plant Perilla Frutescens to Perform Phytoremediation in Cadmium-Contaminated Soils

Perilla frutescens is widely distributed and considered to be an accumulator plant for heavy metals, including cadmium (Cd). However, the phytoremediation ability of P. frutescens is lower than the other hyperaccumulators or accumulators. To improve the phytoremediation ability of P. frutescens to Cd, different concentrations of abscisic acid (ABA) were applied to P. frutescens grown in Cd-contaminated soil to improve its phytoremediation ability. The concentrations of 5, 10, and 20 mu mol/L ABA increased the shoot biomass and contents of photosynthetic pigments (chlorophyll a, chlorophyll b, total chlorophyll and carotenoids) of P. frutescens, while 1 mu mol/L ABA had no significant effect. Different concentrations of ABA enhanced the activities of superoxide dismutase and peroxidase of P. frutescens but had no significant effect on the activity of catalase, while it reduced the contents of soluble protein and malondialdehyde. Different concentrations of ABA increased the contents of Cd in various organs of P. frutescens, and the contents of Cd in stems, leaves, and shoots tended to increase in parallel with the concentrations of ABA. Varying amounts of ABA also increased the Cd extractions by various organs of P. frutescens, and the concentrations of 1, 5, 10, and 20 mu mol/L ABA increased the shoot Cd extraction by 11.26%, 32.24%, 36.18%, and 35.96%, respectively, compared with the control. Therefore, ABA could improve the ability of P. frutescens to perform phytoremediation when grown in Cd-contaminated soil, and the optimal concentration of ABA was 5 mu mol/L.