Effect of light and nitrates on nitrate reductase activity and stability in seedling leaves of selected barley genotypes

Parental genotypes (cv. Aramir and line R567) and the selected doubled haploid (DH) lines C23, C47/1, C41, C55 did not differ in NR activity when they grew on a nutrient solution containing 10 mM KNO₃ and were illuminated with light at 124 μmol·m⁻²·s⁻¹ intensity. A decrease of nitrate content in the nutrient medium to 0.5 mM at 44 μmol·m⁻²·s⁻¹ light intensity caused a significant reduction of NR activity in the parental genotypes as well as in the lines C41 and C55. An increase in light intensity to 124 μmol·m⁻²·s⁻¹ raised NR activity in the leaf extracts of these genotypes. However, independently of light intensity, a high level of this enzyme activity was maintained in the line C23 growing on the nutrient medium with 10 mM and 0.5 mM KNO₃. The NR activity in that line dropped only when nitrate content in the medium decreased to 0.1 mM. NR in the leaves of the line C23, as compared to C41, was characterized by a higher thermal stability in all experimental combinations. An increase in light intensity had no significant influence on NR thermal stability in the leaves of the line C41, but induced a significant increase of this enzyme stability in the line C23. The lines C23 and C41 growing on the nutrient medium with 0.5 mM KNO₃ differed appreciably by nitrate concentration in leaves. A higher accumulation of nitrates was detected in the leaves of the line C41.