Effect of Nitrate Reductase Deficiency upon Growth, Yield, and Protein in Barley1

Abstract

Two nitrate reductase (NR)‐deficient mutants, Az 12 and Az 13, and the ‘Steptoe’ control were grown in the field to determine the effect of NR upon growth, N utilization, yield, and grain protein in barley (Hordeum vulgate L.). Although seasonal in vitro and in vivo NR activities in the mutants were less than 10% of the control, total vegetative dry weight, total reduced N, and percent grain protein in the mutants and Steptoe were not significantly different at maturity. Grain yields of both mutants, however, were significantly lower than the control. A greenhouse study indicated that Az 12 could utilize nitrate as a nitrogen source, although not as effectively as the control. These results indicate that harley mutants with very low levels of apparent NR can utilize nitrate as a N source and that NR activity is not closely associated with percent grain protein. At present it is not known whether the low level of NR in the mutants is sufficient to account for the nitrate reduced or whether there is another mechanism for reducing nitrate in plants that is not detected by conventional NR assay techniques.