Exploring the impact of cadmium stress on morphophysiological traits and GhPCS gene expression in upland cotton seedlings

Cadmium (Cd)-contaminated soil has seriously endangered the agricultural ecological environment, food security and human health. The large biomass, strong capacity of Cd accumulation, and non-edible properties of fiber are the characteristics of cotton, which make it unique in both agricultural production and the remediation of Cd pollution in soil. Phytochelatin synthase (PCS) is a key enzyme that catalyzes the synthesis of phytochelatin, and its gene expression is regulated by tissue development and Cd stress. In this experiment, the morphological and physiological characteristics of cotton seedlings were examined, and the PCS gene was cloned and its expression was analyzed in cotton leaves and roots under Cd stress. The results showed that Cd stress caused a decrease in the biomass of roots, stems and leaves of cotton seedlings, and the plants were slender and severely dehydrated, resulting in a decrease in the contents of glutamic acid (Glu), glycine (Gly) and cysteine (Cys), but a increase in the activity of superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), glutathione reductase (GR), and the content of malondialdehyde (MDA). The Cd contents of shoots and roots increased significantly, and the contents of Cu, Mn, Mg, K in shoots and Mn, Mg, K in roots decreased under Cd stress, while Cu in roots increased. A 1473 bp GhPCS gene was cloned, which can encode 491 amino acid residues. With the increasing Cd concentration and the extension of treatment time, the expression of GhPCS gene in leaves and roots showed dose and time effects. The expression of the GhPCS gene in cotton leaves increased to the highest at 48 h under 200 μM Cd, and reached a maximum at 24 h under 400 μM Cd, indicating that the GhPCS gene in leaves was rapidly and actively expressed in response to high concentration of Cd. The expression of GhPCS gene in roots was lower than that in leaves under different Cd concentrations, and reached the maximum at 48 h, indicating that the GhPCS gene in roots had relatively stable adaptability to Cd stress. And Cd stress improved the expression of GhPCS gene, especially in roots, which in turn increased the accumulation of Cd in shoots and roots. This study provides a theoretical basis for further research on the functional characteristics of the GhPCS gene and its molecular mechanism in cotton under Cd pollution in soil.