LEAF WATER POTENTIAL, STOMATAL-RESISTANCE AND ACTIVITIES OF ENZYMES DURING THE DEVELOPMENT OF MOISTURE STRESS IN THE COCONUT PALM

Response of coconut palms (Cocos nucifera L.) to available soil moisture was studied by determination of leaf water potential, psi, stomatal resistance and activities of three enzymes, acid phosphatase (orthophosphoryl monoester phosphohydrolase, (E.C. 3.1.3.2), L-aspartate: 2-oxoglutarate aminotransferase (E.C. 2.6.1.1) and malate dehydrogenase (E.C. 1.1.1.39). Comparison between the irrigated and rainfed palms was made during the course of a six-month period (December 1985 - May 1986) representing increasing drought conditions. A combined effect of soil and atmospheric droughts on the development of stress in terms of high stomatal resistance and low psi was discernible in coconut. Stress-induced changes in enzyme activities was noticed. The threshold psi for the activities of acid phosphatase and L-aspartate: 2-oxoglutarate aminotransferase was determined.