EFFECT OF WATER-STRESS, ABSCISIC-ACID AND PROLINE ON COTTON PLANTS

The effects of matric water potential (psi(m)), proline (P) and abscis ic acid (ABA) on cotton plants were studied. The characteristics exami ned included the stability of leaf membranes, chlorophyll content, chl orophyll stability index, leaf relative water content and dry matter c ontent. Membrane stability was assessed by determining leakage of elec trolytes from leaf discs exposed to heat and dehydration stress. The m embrane of water-stressed plants was less stable than unstressed plant s. Discs taken from water-stressed plants at (psi(m)) = -0.5 and -1.5 MPa leaked more under heat stress than those taken from unstressed pla nts. The reverse was true under dehydration stress. Decreasing (psi(m) ) reduced chlorophyll a and chlorophyll b content and stability to hea t, leaf relative water content and dry matter accumulation. Proline ei ther alone, or in combination with ABA, significantly enhanced chlorop hyll content, as well as the chlorophyll stability index, leaf relativ e water content and dry matter accumulation especially at low water po tentials. Leaf relative water content was significantly higher in ABA- treated plants at higher stress level. The results proved that sprayin g cotton plants grown under conditions of low soil water potential wit h ABA and proline solutions counteracted the effects of stress especia lly at moderate and high stresses.