The effects of matric water potential (Ψm), proline (P) and abscisic acid (ABA) on cotton plants were studied. The characteristics examined included the stability of leaf membranes, chlorophyll content, chlorophyll stability index, leaf relative water content and dry matter content. Membrane stability was assessed by determining leakage of electrolytes from leaf discs exposed to heat and dehydration stress. The membrane of water-stressed plants was less stable than unstressed plants. Discs taken from water-stressed plants at (Ψm) =−0·5 and −1·5 MPa leaked more under heat stress than those taken from unstressed plants.
The reverse was true under dehydration stress. Decreasing (Ψm) reduced chlorophyll a and chlorophyll b content and stability to heat, leaf relative water content and dry matter accumulation. Proline either alone, or in combination with ABA, significantly enhanced chlorophyll content, as well as the chlorophyll stability index, leaf relative water content and dry matter accumulation especially at low water potentials. Leaf relative water content was significantly higher in ABA-treated plants at higher stress level. The results proved that spraying cotton plants grown under conditions of low soil water potential with ABA and proline solutions counteracted the effects of stress especially at moderate and high stresses.
