Properties of nitrate reductase from seedling leaves of selected barley genotypes

Crude extracts from leaves of 6-day barley seedlings of parental genotypes (cv. Aramir and primitive line R567) and selected doubled haploid (DH) lines were not found to have significant differences in the NADH:NR activity, while considerable differences between these genotypes were shown by the NAD(P)H:NR activity. The cv. Aramir and DH lines did not differ by nitrate accumulation in the leaves. However, the primitive line R567, as compared to the remaining genotypes, was characterized by an appreciably lower ability to accumulate nitrates. In partially purified leaf extracts, significant differences in total NADH:NR activity and in distal activity dependent on methyl viologen (MV:NR) were found between the parental genotypes and selected DH lines. The studied genotypes differed also in dehydrogenase NR activity, i.e. cytochrome c reductase activity in crude extracts. In the studied genotypes, the NADH:NR activity in partially purified leaf extracts did not substantially differ by Km values for nitrates. Calculated Vmax values for NADH:NR in these genotypes were similar to total NR activity in partially purified extracts. Significant differences between the parental genotypes and selected DH lines were found in the thermal NADH:NR stability in crude and partially purified leaf extracts. From the performed studies it follows that different NR stability was one of the reasons of revealed differences in total activity and in partial NR activities in the leaf extracts between the studied genotypes of spring barley. Besides, it is suggested that varied NR gene expression in the leaves of these barley genotypes could also influence NR activity.