RESUMO

Ascorbic acid (AA) is a major redox buffer in plant cells. The role of ethylene in the redox signaling pathways that influence photosynthesis and growth was explored in two independent AA deficient Arabidopsis thaliana mutants (vtc2-1 and vtc2-4). Both mutants, which are defective in the AA biosynthesis gene GDP-L-galactose phosphorylase, produce higher amounts of ethylene than wt plants. In contrast to the wt, the inhibition of ethylene signaling increased leaf conductance, photosynthesis and dry weight in both vtc2 mutant lines. The AA-deficient mutants showed altered expression of genes encoding proteins involved in the synthesis/responses to phytohormones that control growth, particularly auxin, cytokinins, abscisic acid, brassinosterioids, ethylene and salicylic acid. These results demonstrate that AA deficiency modifies hormone signaling in plants, redox-ethylene interactions providing a regulatory node controlling shoot biomass accumulation.

Assuntos

Proteínas de Arabidopsis/genética , Ácido Ascórbico/metabolismo , Etilenos/metabolismo , Monoéster Fosfórico Hidrolases/genética , Reguladores de Crescimento de Plantas/metabolismo , Ácido Abscísico/metabolismo , Arabidopsis/genética , Arabidopsis/metabolismo , Proteínas de Arabidopsis/metabolismo , Ácido Ascórbico/genética , Biomassa , Regulação da Expressão Gênica de Plantas , Mutação , Oxirredução , Monoéster Fosfórico Hidrolases/metabolismo , Fotossíntese/genética , Reguladores de Crescimento de Plantas/genética , Ácido Salicílico/metabolismo , Transdução de Sinais/genética

RESUMO

The equilibrium adsorption at 20 degreesC of molybdophosphoric acid solutions, using ethanol-water as solvent, on titania was studied. The molybdenum adsorption isotherm showed a sigmoidal shape; low values of molybdenum adsorbed were observed for final equilibrium concentrations lower than 50 mg Mo/ml, and for higher concentrations, the adsorbed molybdenum amount almost reached a plateau. From this isotherm it could be concluded that the solute-support interaction was not strong. UV-visible and NMR spectra of the solutions before and after the adsorption on titania showed that the species PMo12O3-40 was present. This species also was observed by DRS in the wet samples and by NMR, FT-IR, and DRS, in the solid samples dried at room temperature and calcined at 255, 310, 365, and 425 degreesC, showing that the thermal stability of molybdophosphoric acid adsorbed on titania is similar to that of the bulk acid. The impregnating solutions and the impregnated solid changed with the time to a bluish color as a consequence of the formation of heteropoly blues which presented Mo6+ partially reduced to Mo5+. The XRD patterns indicated that the species adsorbed onto the support surface are highly dispersed like a noncrystalline form. Copyright 1998 Academic Press.