Effects of melatonin on cadmium accumulation in the accumulator plant Perilla frutescens

To enhance the phytoremediation ability of the heavy metal accumulator Perilla frutescens, melatonin (MT) was applied at different concentrations (0, 25, 50, 100, 150, and 200mol/L) to P.frutescens growing in cadmium (Cd) contaminated soil (10mg/kg). The MT treatments increased the root and shoot biomasses of P.frutescens, with the maximum increase in the 150mol/L MT treatment (79.51% and 36.18% higher, respectively, than those of the control). The MT treatments also enhanced superoxide dismutase activity, peroxidase activity, and the soluble protein concentration of P.frutescens, and 100-200mol/L MT increased the chlorophyll a, chlorophyll b, and total chlorophyll concentrations in P.frutescens. The MT treatments increased the Cd concentrations in roots and shoots of P.frutescens in a dose-dependent manner. Different MT concentrations increased the Cd accumulation amounts of roots and shoots of P.frutescens, with the maxima accumulation amounts in the 150mol/L MT treatment (226.98% and 85.89% higher, respectively, than those of the control). These results show that MT can promote the growth and phytoremediation ability of P.frutescens growing in Cd-contaminated soil, and the optimum MT dose is 150mol/L.