Abstract
Water deficit is a main constraint on crop production in the semi-arid areas. Cowpea (Vigna unguiculata (L.) WALE) is one of the most drought resistant crops. Gene expression of aquaporins, water channel proteins, is induced by water stress indicating the necessity of facilitated water transport to the shoot. In order to identify the drought resistant characteristics in cowpea plants, transpiration rate, water content of leaves and roots in relation to aquaporin were studied. Following transpiration rate of cowpea leaves markedly decreased with the decrease in soil water until 7 days after treatment (DAT), it proceeded with minor change during 45 DAT while there was no change in water content of leaves and roots throughout the drought stress. Aquaporin-related proteins with a relative molecular mass of 30 kDa were detected in microsomal membrane fractions extracted from leaf and root tissues of both control and drought-stressed cowpea plants by immunoblot with an anti-aquaporin specific antibody. As a result, there were no differences in drought stress as well as organs. Interestingly, phosphorylation of serine residue at 30 kDa as a same size with the aquaporin-related protein, was detected in microsomal polypeptides extracted from roots of drought- stressed cowpea, but not in those of leaves. These results indicate that further studies on phosphorylation of aquaporins will reveal the water status characterizing the marked drought resistance in cowpea.
