FOLIAR ABSCISIC ACID (ABA) CONCENTRATION AND LEAF GAS EXCHANGE PROPERTIES OF JATROPHA CURCAS SUBJECTED TO WATER STRESS

International interest in Jatropha curcas as a drought tolerant, fast-growing \ncrop, suitable for bio-energy production, has grown significantly in recent \nyears. The effective management of commercially planted species in terms of \npossible water resource impacts requires accurate information on water use \nand bio-physical production characteristics relevant to areas having planting \npotential. Currently there is no knowledge on the type of water regimes \nsuitable for the survival, growth and yield performances of J. curcas \nparticularly in Sarawak which seems to be receiving rainfall all year round. \nFoliar abscisic acid (ABA) concentration and leaf gas exchange properties of \nJatropha curcas subjected to water stress were examined. Foliar ABA \nconcentration of J. curcas increased to 5 fold while its leaf stomatal \nconductance (gs) was reduced by 31 % as the soil water potential decreased \nfrom field capacity to more than 1.5 MPa. Photosynthetic rates (A) of plants \ngrown under control conditions were higher with mean values ranging from \n13.69 to 20.27 μmol m-2 \ns \n-1 \ncompared to those under water-stress with mean \nvalues ranging from 8.39 to 15.47 μmol m-2 \ns \n-1 \n. Photosynthetic rates were \nhowever reduced by 41 to 39 % from April to July after as the soil water \npotential decreased from field capacity to > 1.5 MPa indicating that water \nstress depressed photosynthetic capacity of J. curcas. A strong relationship \nbetween A and gs regardless of treatments (r2 = 0.86) was observed indicating \nthat photosynthesis was closely related to the changes in the leaf stomatal \nconductance and overall plant growth performance was closely correlated to \nphotosynthetic rates. Under water stress, the fivefold increment of foliar ABA \nassisted plant in adaptation to drought stress through stomata closure thus \nreducing excessive transpiration. The combinations of physiological \nmechanisms that effectively postpone dehydration and minimize damage \nenable this species to survive in hostile environment with unpredictable \nprecipitation.