GENOTYPIC VARIATION IN WATER STRESS-RESPONSIVE ALDOSE REDUCTASE ACTIVITY IN RICE: IDENTIFICATION OF A STRESS INSENSITIVE ALDOSE REDUCTASE VARIANT

School of Life Sciences, University of Hyderabad Hyderabad-500 046, A. P INDIA

Aldose reductase (alditol: NAD (P)+ 1- oxidoreductase, EC 1.1.1.21) a member of the monomeric, NADPH dependent aldoketoreductase family catalyzing the stereospecific reduction of a number of aldehydes including glucose to the corresponding sugar alcohol sorbitol (Nishimura et al, 1990). They are well conserved in plants and animals. In humans they are reported to be involved in diabetic complications and hyperglycemia. In plants not much is known about the role of aldose reductases. We have screened rice cultivars for the presence of aldose reductase and its response to water stress and ABA. Aldose reductase has been identified in late maturing or mature embryos of several indica rice cultivars. Significant quantitative variation in the enzyme activity between tested indica rice genotypes has been observed. Western blot data also revealed genotypic variation. All of the tested rice lines accumulate AR in embryos but not in vegetative tissue. These lines are classified by breeders as relatively drought tolerant. Further, all but one of these genotypes when subjected to dehydration stress or exogenous application of ABA accumulates AR in vegetative tissue. On the contrary, an indica genotype Hamsa, (drought sensitive) does not accumulate AR in vegetative tissues under water stress and ABA suggesting this line represents a regulatory variant. There is correlation between stress-induced aldose reductase activity and the protein level. Further we detected AR protein in other cereals by using anti-AR antibodies raised against barley embryo protein. This, to our knowledge, is the first report of identification of AR in rice. Its possible role in drought tolerance in rice will be discussed.