Aldose reductase in rice (Oryza sativa L.): stress response and developmental specificity.

Aldose reductase (AR) protein and enzyme (alditol: NAD (P)(+) 1-oxidoreductase, EC 1.1.1.21) activity have been identified in mature seeds of indica rice cultivars. The protein begins to accumulate 15 days after pollination, reaches a peak at seed maturity and disappears upon imbibition. Furthermore, AR is induced in vegetative tissues in response to exogenous ABA application and other stress conditions, such as PEG mediated water stress and salinity. Increase in AR protein levels upon stress are in close agreement with a similar increase in enzyme activity. Varietal differences in AR levels have been demonstrated. Interestingly, all tested tolerant cultivars (as denoted by breeders) accumulate AR in vegetative tisssue in response to ABA application, while the sensitive line, Hamsa, does not do this under similar stress conditions, suggesting that AR may be associated with stress tolerance. Furthermore, AR protein has been identified in mature seeds of some selected cereals indicating the conserved nature of AR across grasses.