Physiological Responses of Cotton (Gossypium hirsutum L.) to Salt Stress
Mohammad Pessarakli
Abstract
Cotton plants grown in normal (control) and NaCl-treated Hoagland solutions were studied at two stages of growth (vegetative and reproductive). Plant growth in terms of dry-matter production was measured. Nitrogen absorption (total N and 15N) and water uptake were determined. Plant parts (shoots and roots) were analyzed separately for N content and distribution of 15N in ammonium plus amide-N, free amino-N, total soluble-N, and protein-N after the plants were provided 15NH4NO3 in nutrient solutions for 6, 12, and 24 h. The metabolism of 15N in salinized cotton plants was adversely affected under medium and high levels of NaCl, at both vegetative and reproductive stages of growth. Significant accumulations of all soluble-15N fractions occurred when plants were subjected to medium and high levels of NaCl compared with the controls. The −0.4 MPa osmotic potential of the culture solution enhanced protein synthesis at the vegetative growth stage. Only the −1.2 MPa osmotic potential significantly decreased the protein-15N content of plants as compared with the controls and any other level of NaCl. Protein synthesis was impaired by a large excess of NaCl in the nutrient solution, which inhibited NH 4 + metabolism. Consequently, under salt-stress conditions of sufficient magnitude, plant growth, N absorption and metabolism, protein synthesis, and water absorption will be altered. This will result in the failure of plants to fully utilize nutrients and water. Salinity levels in excess of those causing drastic interference with plant growth, nutrient (i.e., N) absorption and metabolism, and water uptake in salt-sensitive plants such as beans do not appreciably interfere with these factors in cotton, a relatively high-salt-tolerant plant. This indicates a link between salt tolerance, growth, nutrient (i.e., N) absorption and metabolism, and water uptake. Although the contribution of osmotic and specific ion effects cannot be distinguished from this study, it is likely that both were involved.