OSMOTIC ADJUSTMENT OF COTTON TO MODERATE KCL STRESS AND SUBSEQUENT WATER-STRESS DURING EARLY STAGES OF DEVELOPMENT

High KCl fertilization of drip irrigated cotton (Gossypium hirsutum L.) under intensive growth conditions, mainly in wheat (Triticum aestivum L.) cotton double cropping when the soil profile is dried out and the cotton has a restricted root volume, may cause moderate osmotic stress. Therefore, the response of cotton to KCl stress and successive water stress was evaluated by measurements of leaf water potential (.psi.L), osmotic potential (.psi.S), turgor pressure (P), and mineral composition of leaves and flower buds. Young cotton plants (var. Acala SJ2) grown in 10-L plastic pots filled with a peat/tuff mixture (1:1) in a field environment were exposed to prolonged osmotic stress for 35 days by application of KCl. Electrical conductivity of the nutrient solutions was 1.5, 3.6, 6.7, 9.8, and 13 dS m-1, and the final .psi.S of the growth medium at the time of measurement 65 days after planting was 0.05, 0.16, 0.27, 0.38, and 0.47 MPa, respectively. The prolonged 35-day long KCl stress caused stunting of vegetative growth and reduced .psi.L, which was accompanied by reduction in .psi.S and maintenance of positive P. Osmotic adjustment was also observed in developing flower buds, but their .psi.S was higher than leaf .psi.s. The main contribution to osmotic adjustment was from the accumulation of inorganic minerals such as K+ and Cl- in leaves and flower buds. Exposure of the control and KCl-treated plants to successive water stress by withholding irrigation reduced .psi.L in both treatments. Plants from the KCl treatment responded by a concomitant decrease in .psi.S, which enabled maintenance of positive P, whereas the control plants that were exposed to water stress did not show osmotic adjustment. The results indicate that prolonged KCl stress enabled the cotton plant to exist and withstand successive water stress, but the cotton plant could not overcome growth inhibition.