Glycolate Oxidase Isozymes Are Coordinately Controlled by GLO1 and GLO4 in Rice

Glycolate oxidase (GLO) is a key enzyme in photorespiratory metabolism. Four putative GLO genes were identified in the rice genome, but how each gene member contributes to GLO activities, particularly to its isozyme profile, is not well understood. In this study, we analyzed how each gene plays a role in isozyme formation and enzymatic activities in both yeast cells and rice tissues. Five GLO isozymes were detected in rice leaves. GLO1 and GLO4 are predominately expressed in rice leaves, while GLO3 and GLO5 are mainly expressed in the root. Enzymatic assays showed that all yeast-expressed GLO members except GLO5 have enzymatic activities. Further analyses suggested that GLO1, GLO3 and GLO4 interacted with each other, but no interactions were observed for GLO5. GLO1/GLO4 co-expressed in yeast exhibited the same isozyme pattern as that from rice leaves. When either GLO1 or GLO4 was silenced, expressions of both genes were simultaneously suppressed and most of the GLO activities were lost, and consistent with this observation, little GLO isozyme protein was detected in the silenced plants. In contrast, no observable effect was detected when GLO3 was suppressed. Comparative analyses between the GLO isoforms expressed in yeast and the isozymes from rice leaves indicated that two of the five isozymes are homo-oligomers composed of either GLO1 or GLO4, and the other three are hetero-oligomers composed of both GLO1 and GLO4. Our current data suggest that GLO isozymes are coordinately controlled by GLO1 and GLO4 in rice, and the existence of GLO isozymes and GLO molecular and compositional complexities implicate potential novel roles for GLO in plants

Hormesis with glyphosate depends on coffee growth stage

Os sistemas de manejo de plantas daninhas em quase todos os pomares de café do Brasil permitem que o herbicida pulverizado sofra deriva sobre a cultura. Com objetivo de avaliar se há algum efeito do glyphosate, herbicida mais comumente utilizado em pomares de café, sobre as plantas de café, uma ampla faixa de doses do herbicida foi aplicada diretamente sobre plantas de café em dois distintos estádios de crescimento da planta. Embora o crescimento de ambas as plantas novas e velhas tenha sido reduzido em doses mais altas de glyphosate, baixas doses não causaram efeitos sobre características de crescimento de plantas novas e estimularam o crescimento das mais velhas. Portanto, o efeito hormético do glyphosate é dependente do estádio de crescimento da planta de café no momento da aplicação do herbicida.Weed management systems in almost all Brazilian coffee plantations allow herbicide spray to drift on crop plants. In order to evaluate if there is any effect of the most commonly used herbicide in coffee production, glyphosate, on coffee plants, a range of glyphosate doses were applied directly on coffee plants at two distinct plant growth stages. Although growth of both young and old plants was reduced at higher glyphosate doses, low doses caused no effects on growth characteristics of young plants and stimulated growth of older plants. Therefore, hormesis with glyphosate is dependent on coffee plant growth stage at the time of herbicide application.Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)Universidade do Estado de Santa Catarina (UDESC) Centro de Cencias Agroveterinarias Departamento de AgronomiaUniversidade Estadual Paulista Faculdade de Cencias Agrarias e Veterinarias Departamento de Biologia Aplicada a AgropecuariaUniversity of Mississippi Natural Products Utilization Research Unit United States Department of AgricultureUniversidade Estadual Paulista Faculdade de Cencias Agrarias e Veterinarias Departamento de Biologia Aplicada a Agropecuari

Variation in net photosynthesis, rubisco activity and chloroplast ultrastructure among somatic hybrids of Solanum tuberosum and S. brevidens

The effect of ploidy, parental chloroplast type and parental nuclear genome dosage on net photosynthesis, Rubisco activity and chloroplast ultrastructure was studied among somatic hybrids of diploid S. brevidens and dihaploid S. tuberosum. An increase in nuclear ploidy resulted in an increase in net photosynthesis and specific leaf weight. There were no significant differences in net photosynthesis or Rubisco activity between the hybrids having different parental chloroplast type. Examination of the hexaploid hybrids indicated that Rubisco activity was affected by nuclear-organelle genome incompatibility, the most affected combination being tuberosum chloroplast type with brevidens nuclear genome. Examination of chloroplast ultrastructure revealed wide variation in the size of chloroplasts, starch granules, plastoglobuli and in grana stacking among the hybrids and between fusion parents

A nocturnal inhibitor of carboxylation in leaves

The diurnal variation in the activity of ribulose-l,5-bisphosphate carboxylase (RuBPCase), the major CO2-fixing enzyme in plants, has been shown to result from the influx and efflux of Mg2+ ions into and out of the chloroplast stroma. A recent re-examination of the phenomenon indicates that the inactivation of the enzyme, rather than being due to the efflux of Mg2+, is correlated in some plant species with an increase in the concentration of an organic phosphate ester in the chloroplast in the dark1-3. We have purified this potent inhibitor from dark-treated potato (Solanum tuberosum) leaves, and established that its structure is 2-carboxy-D-arabinitol-1-phosphate, a molecule that closely resembles an intermediate in the carboxylase reaction of RuBPCase