Assuntos
DNA Complementar/genética , Biblioteca Gênica , Técnicas de Amplificação de Ácido Nucleico , Reação em Cadeia da Polimerase/métodos , Arabidopsis/genética , Clonagem Molecular/métodos , Primers do DNA/genética , DNA de Plantas/genética , Eletroforese em Gel de Ágar , Proteína Ribossômica L3 , Proteínas Ribossômicas/genéticaRESUMO
Two clones of Arabidopsis thaliana possessing high sequence identity to the yeast gene encoding ribosomal (r) protein L3 were isolated by heterologous DNA hybridization. The coding regions of these two clones have approx. 63% amino acid (aa) sequence identity to the yeast L3 r-protein and 85% aa sequence identity to each other. Both genes are expressed in shoots. The presence of two divergent genes in A. thaliana raises the possibility that the gene products participate in the formation of functionally distinct ribosomes.
Assuntos
Evolução Biológica , DNA/biossíntese , Plantas/genética , Proteínas Ribossômicas/genética , Alelos , Sequência de Aminoácidos , Sequência de Bases , Clonagem Molecular , Citoplasma/metabolismo , Dados de Sequência Molecular , Mutação , Plantas/efeitos dos fármacos , Proteína Ribossômica L3 , Saccharomyces cerevisiae/efeitos dos fármacos , Saccharomyces cerevisiae/genética , Homologia de Sequência do Ácido NucleicoRESUMO
A population of A. thaliana, produced by self-fertilization of ethylmethane sulfonate treated plants, was exposed to chlorate in the watering solution, and plants showing early susceptibility symptoms were rescued. Among the progeny lines of these plants five were shown to be repeatably chlorate-hypersusceptible. One of these lines (designated C-4) possessed elevated activity of nitrate reductase (NR). The NR activity of mutant C-4 was higher than that of normal plants throughout the life cycle. Nitrite reductase and glutamine synthetase activities of C-4 were normal, as were chlorate uptake rate and tissue nitrate content. The elevated NR activity apparently was responsible for the chlorate hypersusceptibility of C-4. Inheritance studies of NR indicated that the elevated activity of C-4 was probably controlled by a single recessive allele.
RESUMO
Races of a C3 plant species, Arabidopsis thaliana, were screened for time of survival when enclosed in an air-tight chamber with a C4 plant species (Zea mays L.). This has been suggested as a method of detecting and selecting for increased photosynthetic efficiency among C3 genotypes. The C4 plant should, in such conditions, reduce the atmospheric CO2 concentration below the compensation point of the C3 plant, resulting in its eventual death. Significant differences were found among the A. thaliana races for survival time; some races survived only one week in competition with corn while others survived more than two weeks. Two races, chosen for contrasting survival in closed chambers, were hybridized and compared to their F2 progeny for survival time. Substantial genetic segregation occurred among the F2, and a number of transgressive segregates having survival times superior of both parents were identified. Also significant heterosis was observed in the F2 population.
RESUMO
Nitrate reductase activity is most commonly assayed by measurement of product formation. Excess NADH and factor(s) present in the enzyme extract that interfere with the diazotization and azo color complex of nitrite cause a depression of apparent nitrate reductase activity. Two postassay treatments were found that markedly enhanced the extent of nitrite color formation and apparent nitrate reductase activity. The procedure involves stopping the reaction with zinc acetate (50 mumoles per ml of reaction mix), followed by removal of the precipitate by centrifugation. Presumably the zinc acetate removes extract factor(s) that interfere with color development, because it does not remove the NADH. Phenazine methosulfate (15 nmoles per ml of reaction mix) is added to aliquots of the supernatant and allowed to stand for 20 min at 30 C to oxidize the residual NADH before color development.
