II. 27. Nitrate reductase-deficient mutants in barley.
A. Kleinhofs, T. Kuo and R. L. Warner, Department of Agronomy and Soils and Program in Genetics, Washington State University, Pullman, Washington 99164, U.S.A.
We have isolated nitrate reductase (NR)-deficient mutants in barley by screening individual M2 seedlings from azide mutagenized material (Kleinhofs et al., 1978). The first three mutants obtained have been previously described (Warner et al., 1977). In this report we describe additional mutants with respect to their enzymic phenotype as well as allelism. Gene designations are proposed.
For techniques in mutation induction, selection and enzyme assays, please refer to the above cited papers.
The mutants described here have been self-propagated for several generations now. The characteristics described have been invarient. Most of the mutants are clearly different with respect to several enzyme activities (Table 1). Thus, Az 29 and Az 34 are completely lacking in any detectable in vivo NR activity, while Az 12, Az 13, Az 23, Az 28 and Az 31 show a very low level (0.1-4.3% of control) of activity. The mutants Az 30, Az 32, and Az 33 have substantial in vivo NR activity ranging from 11.8 to 26.4% of the control activity. All the mutants except Az 34 have very low, but not zero, NADH NR activity (Table 1). The mutant Az 34 seems to have a somewhat higher NADH NR activity (5.5% of the control). All the mutants are lacking in FMNH2 NR activity except Az 32 which is higher than the control (Table 1). The cytochrome C reductase (CR) activity shows three different classes of mutants, i.e., those with CR activity comparable to uninduced wild type controls thus lacking the inducible NR associated CR activity (Az 12, Az 23, Az 29, Az 30, and Az 32), those with intermediate CR activity (Az 13, Az 31, Az 33, and Az 34), and those with much higher than normal CR activity (Az 28). The nitrite reductase (NiR) activity is elevated above normal levels in all of the mutants. The mutant Az 29 seems to be somewhat different in that here the NiR activity is only slightly above normal.
Table 1. Nitrate (NR), nitrite (NiR), and cytochrome
C reductase (CR) activities in 7-day-old nitrate reductase mutant and control
seedlings grown with nitrate.
All enzyme activities of the mutants expressed as
percent of the control.
Allelism tests were conducted by intercrossing the mutants in all possible combinations. The crosses were made in 1976-78. The individual F1 seedlings were tested for NADH NR activity. Nine out of the ten mutants showed a lack of complementation for NR activity, indicating that they are allelic (Table 2). The F1 seedlings of the cross Az 34 with Az 12 contained approximately one-half the NR activity of the wild type control indicating complementation and non-allelism (Table 2).
Table 2. Allelism test of NR-deficient mutants.
A more detailed characterization of these mutants is being prepared for publication.
References
Kleinhofs, A., R. L. Warner, F. J. Muehlbauer and R. A. Nilan, 1978. Induction and selection of specific gene mutations in Hordeum and Pisum, Mutation Res., 51:29-35.
Warner, R. L., C. J. Lin and A. Kleinhofs, 1977. Nitrate reductasedeficient mutants in barley, Nature 269:406-407.
