MULTIPLE FORMS OF NITRATE REDUCTASE AND THEIR ROLE IN NITRATE ASSIMILATION IN ROOTS OF WHEAT AT LOW-TEMPERATURE OR HIGH SALINITY

NADPH-, NADH-, and KNO3-eluted fractions of nitrate reductase (NR) were isolated from roots of winter wheat (Triticum aestivum L. cv. Mironovskaya 808) grown under low temperature or high salinity. All three fractions exerted activity with either NADPH or NADH as electron donor. The NADPH-eluted Fraction showed the highest activity with NADPH, whereas the NADH- and KNO3-eluted fractions were most active with NADH. The NADH- and NADPH-dependent activities in the NADH- and KNO3-eluled fractions were the ones that changed the most in response to low temperature. The inhibitory effect of salt stress was the same for both activities in each of the NADH- and KNO3-eluted fractions. The NADPH-eluted NR was the one least affected by the growth conditions.