Mutants Of Higher Plants Research Articles

Nitrate reductase-deficient mutants in barley

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 barley2,3. Nitrate reductase, which has an important function in higher plants4, has been extensively studied in bacteria and fungi5, is highly regulated5,6, 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.

The Inheritance of Genes in Mitochondria and Chloroplasts

Among all the areas of biological science, genetics is one of the most beautifully exact and formal in its structure. The subject is built upon a framework of precisely formulated laws of great generality, and most of those laws are firmly grounded in mechanistic explanations in terms of the behavior of cells, chromosomes, and molecules. One aspect of heredity has largely resisted such treatment: the study of organelle genes, which are located inside mitochondria or chloroplasts and consequently are inherited via the cytoplasm. The first cases of cytoplasmic inheritance, later shown to involve plastid genes, were discovered by Correns (1909) and Baur (1909) just a few years after the rediscovery of the Mendelian laws, which describe the inheritance of nuclear genes. The next 50 years saw the discovery of more instances of plastid mutants in higher plants (reviewed by Kirk and Tilney-Bassett 1967) and in algae (reviewed by Sager 1972), and the first cases of mitochondrial gene mutants (Ephrussi et al. 1949, Mitchell and Mitchell 1952). But the investigation of these phenomena lagged far behind that of the more numerous and more easily studied nuclear genes; some geneticists were reluctant to believe in the existence, let alone the importance, of genes in the cytoplasm. Then, in the early 1960's, the discovery of DNA in plastids (Chun et al. 1963, Ris and Plaut 1962, Sager and Ishida 1963) and in mitochondria (Luck and Reich 1964, Nass and Nass 1963, Schatz et al. 1964) made the study of genes in these organelles respectable, and the study of their unique DNA's has virtually become a scientific bandwagon. Nevertheless, scientists are still far from a clear

Defined mutants in higher plants.

This chapter briefly reviews work on mutant selection using somatic cells of higher plants and then describes experiments designed to recover agriculturally useful variants. Mutants of Nicotiana tabacum were recovered which were resistant to an analog of methionine. These plants were found to be much less susceptible to damage by the pathogen Pseudomonas tabaci, which produces a toxin that is an analog of methionine. Several mutants show a specific increase in the level of free methionine.KeywordsMutant PlantNecrotic SpotAuxotrophic MutantMutant SelectionSelective TechniqueThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Production of auxotrophic mutants in ferns.

A method has been devised for the selection of auxotrophic mutants in higher plants. The method depends upon the incorporation of BUdR into the DNA of non-auxotrophic cells and upon its lack of incorporation into the DNA of auxotrophic cells. A wide range of auxotrophic types were recovered.

The influence of different light intensities on the growth of the tobacco aurea mutant Su/su

Chlorophyll mutants in higher plants are often injured by high light intensities [see 14, 24]. By contrast a dominant aurea mutant in tobacco, Su/su, which was discovered by BURK and MENSER in 1964 [2], requires high light intensities for normal growth. The mutation has apparently produced a sun plant in which the inherited loss of light-absorbing pigments has been made up by an increased capacity for using light. Numerically, this characteristic is expressed by a maximal rate of photosynthesis of 230 μl O2 evolved/mg chlorophyll per min, whereas the green control var. John Williams Broadleaf only gives 45 μl O2 evolved/mg chlorophyll per min. Similar, but not as large, metabolic ratios seem to prevail between other normal green plants and their yellow-green derivatives, like Nicotiana tabacum Rg, Fla. 15, No. 63 and Dixie Shade.

Studies of growth & metabolism of a barley mutant lacking chlorophyll b

In an earlier paper (7) the chlorophyll composition of a number of chlorina mutants of barley obtained from D. W. Robertson (10) were described and it was then pointed out that one of the mutants appeared to be entirely lacking in chlorophyll b. Thus, it was of considerable interest to learn whether the chlorophyll b deficiency was affecting the photosynthetic activity of this mutant. Comparative studies on the photosynthetic activities in white light of the normal type (containing chlorophyll a & b) and of the mutant as well as studies on their respiratory behavior in the dark and in the light are reported here. In addition, some effort has been made to ascertain whether chlorophyll b could possibly be detected in the chlorophyll b deficient mutant by means of the more sensitive fluorescence analysis of chromatographed pigment extracts. Chlorophyll b deficient mutants in higher plants first were described by Eyster (4) in maize and more recently by Robbelen (9) in Arabidopsis. However, the plants described by these investigators did not survive the seedling stage-dying rather early in their life cycles. In contrast, the barley mutant employed in the investigations described here can complete its life cycle and thus should be of considerable usefulness in continued investigations on the role of chlorophyll b in the photo-metabolism of higher plants. Materials & Methods