Physiological and Biochemical Properties of Cotton Seedlings in Response to Cu²⁺ Stress

Copper(II) (Cu2+) is essential for plant growth and development. However, high concentrations are extremely toxic to plants. We investigated the tolerance mechanism of cotton under Cu2+ stress in a hybrid cotton variety (Zhongmian 63) and two parent lines with different Cu2+ concentrations (0, 0.2, 50, and 100 mu M). The stem height, root length, and leaf area of cotton seedlings had decreased growth rates in response to increasing Cu2+ concentrations. Increasing Cu2+ concentration promoted Cu2+ accumulation in all three cotton genotypes' roots, stems, and leaves. However, compared with the parent lines, the roots of Zhongmian 63 were richer in Cu2+ and had the least amount of Cu2+ transported to the shoots. Moreover, excess Cu2+ also induced changes in cellular redox homeostasis, causing accumulation of hydrogen peroxide (H2O2) and malondialdehyde (MDA). Conversely, antioxidant enzyme activity increased, while photosynthetic pigment content decreased. Our findings indicated that the hybrid cotton variety fared well under Cu2+ stress. This creates a theoretical foundation for the further analysis of the molecular mechanism of cotton resistance to copper and suggests the potential of the large-scale planting of Zhongmian 63 in copper-contaminated soils.