Physiological and Biochemical Properties of Cotton Seedlings in Response to Cu 2+ Stress.

Copper(II) (Cu ²⁺ ) is essential for plant growth and development. However, high concentrations are extremely toxic to plants. We investigated the tolerance mechanism of cotton under Cu ²⁺ stress in a hybrid cotton variety (Zhongmian 63) and two parent lines with different Cu ²⁺ concentrations (0, 0.2, 50, and 100 μM). The stem height, root length, and leaf area of cotton seedlings had decreased growth rates in response to increasing Cu ²⁺ concentrations. Increasing Cu ²⁺ concentration promoted Cu ²⁺ accumulation in all three cotton genotypes' roots, stems, and leaves. However, compared with the parent lines, the roots of Zhongmian 63 were richer in Cu ²⁺ and had the least amount of Cu ²⁺ transported to the shoots. Moreover, excess Cu ²⁺ also induced changes in cellular redox homeostasis, causing accumulation of hydrogen peroxide (H ₂ O ₂ ) and malondialdehyde (MDA). Conversely, antioxidant enzyme activity increased, while photosynthetic pigment content decreased. Our findings indicated that the hybrid cotton variety fared well under Cu ²⁺ 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.