Cotton seedling plants adapted to cadmium stress by enhanced activities of protective enzymes

Cotton (Gossypium hirsutum L.) is a global major crop with strong tolerance to abiotic stress, but its tolerance to cadmium (Cd) stress is unclear. The objective of this study was to determine the influence of Cd stress on the seedling growth and some physiological properties of cotton. Cotton seedlings with three fully expended leaves were treated with Cd at different concentrations (0, 25, 50 and 100 μmol/L), and seedling growth, chlorophyll (Chl) content, malonaldehyde (MDA) content, photosynthetic rate, superoxide dismutase (SOD) and peroxidase (POD) activity in the main-stem leaves were measured 5 days or 10 days after stress treatment. It was found that with the increase in the Cd concentration, the SOD and POD activity of the stressed seedlings displayed an increase first and then a decrease. The MDA content increased and the Chl decreased, which finally led to a decline in plant height and leaf area. The results suggest that cotton seedlings were adapted to low-concentration Cd stress by the increased protective enzyme activity, but over 50 μmol/L of Cd concentration would exert a significantly inhibitory effect on the photosynthetic properties and protective enzyme activity of the cotton leaves. Cotton plants can be adapted to low Cd stress by increasing the activity of the protective enzymes.