Nitrate reductase-deficient mutants in barley

Abstract

MUTANTS have long been used to study genetic and biochemical regulation of metabolic pathways in microorganisms. Often it is a relatively simple task to screen large bacterial populations for an individual lacking a specific enzyme or enzyme product. Defined enzyme mutants would also be valuable research tools for plant geneticists and biochemists. Unfortunately, very few biochemically defined mutants have been selected in higher plants, principally because of the genetic and biochemical complexity, and the long generation time of higher plants¹. But, these obstacles could be overcome in plants by inducing high mutation frequencies and developing effective techniques for selecting biochemically defined mutants. High mutation frequencies can be readily induced in some higher plant species by sodium azide, a potent base substitution mutagen in barley^2,3. Nitrate reductase, which has an important function in higher plants⁴, has been extensively studied in bacteria and fungi⁵, is highly regulated^5,6, and has several catalytic activities including NAD(P)H, FMNH₂ and reduced methyl viologen nitrate reductase activities, and NAD(P)H cytochrome c reductase activity⁶. Nitrate reductase is therefore an excellent enzyme in which defined mutants in higher plants can be selected, studied, and compared with microorganisms. We describe here a procedure for the induction and selection of nitrate reductase-deficient mutants in higher plants, and the partial characterisation of three nitrate reductase-deficient mutants in barley.