REGULATION OF MO-COFACTOR, NADH-SPECIFIC AND NAD(P)H-SPECIFIC NITRATEREDUCTASE ACTIVITIES IN THE WILD-TYPE AND 2 NAR-MUTANT LINES OF BARLEY (HORDEUM-VULGARE L)

Seedlings of three genotypes of barley, Hordeum vulgare L., cv, Winer, were grown in nutrient solutions for 12 d: (a) Wt, the wild type; (b) Chlo19 and (c) Chlo29, two nitrate reductase (NR) deficient nar-mutan ts, Nar-mutant plants grown in nitrate developed about 5-24% of NADH-N R (EC 1.6.6.1.) activity level characteristic of the Wt, The NR in vit ro assays in which NADH or NADPH were used as electron donors showed t hat the two mutant lines contained a mixture of NADH-specific and NAD( P)H-bispecific (EC 1.6.6.2.) NRs, Chlo19 had a very low level of MoCo activity as compared to Chlo29 and Wt, Chlo19 appeared to be mutated i n a MoCo gene rather than in the genes coding for the nitrate NR apoen zyme, NAD(P)H-NR was found in the shoots and roots of both mutants but only in the roots of Wt. Several aspects of the regulation of NADH an d NAD(P)H specific NRs in plants of the barley cv. Winer genotypes are discussed, MoCo was a strong limiting factor for NR biosynthesis in n itrate-fed plants of Chlo19, but less limited in N-starved and ammoniu m-fed plants. Biomass production by the three genotypes was similar du ring first 12 d after germination, regardless of the level of NR detec ted in vitro, Mutant plants may be able to supply the nitrogen require d for growth with only 5-24% of the NR level of the WT.