RESUMEN
In order to understand the role of cytosolic antioxidant enzymes in drought stress protection, transgenic tobacco (Nicotiana tabacum cv. Xanthi) plants overexpressing cytosolic Cu/Zn-superoxide dismutase (cytsod) (EC 1.15.1.1) or ascorbate peroxidase (cytapx) (EC 1.11.1.1) alone, or in combination, were produced and tested for tolerance against mild water stress. The results showed that the simultaneous overexpression of Cu/Znsod and apx or at least apx in the cytosol of transgenic tobacco plants alleviates, to some extent, the damage produced by water stress conditions. This was correlated with higher water use efficiency and better photosynthetic rates. In general, oxidative stress parameters, such as lipid peroxidation, electrolyte leakage, and H(2)O(2) levels, were higher in non-transformed plants than in transgenic lines, suggesting that, at the least, overexpression of cytapx protects tobacco membranes from water stress. In these conditions, the activity of other antioxidant enzymes was induced in transgenic lines at the subcellular level. Moreover, an increase in the activity of some antioxidant enzymes was also observed in the chloroplast of transgenic plants overexpressing cytsod and/or cytapx. These results suggest the positive influence of cytosolic antioxidant metabolism on the chloroplast and underline the complexity of the regulation network of plant antioxidant defences during drought stress.
Asunto(s)
Adaptación Fisiológica , Citosol/enzimología , Sequías , Nicotiana/enzimología , Peroxidasas/metabolismo , Estrés Fisiológico , Superóxido Dismutasa/metabolismo , Riego Agrícola , Antioxidantes/metabolismo , Ascorbato Peroxidasas , Ácido Ascórbico/metabolismo , Southern Blotting , Clorofila/metabolismo , ADN Bacteriano/genética , Fluorescencia , Gases/metabolismo , Glutatión/metabolismo , Estrés Oxidativo , Fotosíntesis , Hojas de la Planta/anatomía & histología , Hojas de la Planta/metabolismo , Plantas Modificadas Genéticamente , Nicotiana/fisiología , Transformación GenéticaRESUMEN
Hydrogen peroxide (H(2)O(2)) increased the germination percentage of pea seeds, as well as the growth of seedlings in a concentration-dependent manner. The effect of H(2)O(2) on seedling growth was removed by incubation with 10 microm ABA. The H(2)O(2)-pretreatment produced an increase in ascorbate peroxidase (APX), peroxidase (POX) and ascorbate oxidase (AAO). The increases in these ascorbate-oxidizing enzymes correlated with the increase in the growth of the pea seedlings as well as with the decrease in the redox state of ascorbate. Moreover, the increase in APX activity was due to increases in the transcript levels of cytosolic and stromal APX (cytAPX, stAPX). The proteomic analysis showed that H(2)O(2) induced proteins related to plant signalling and development, cell elongation and division, and cell cycle control. A strong correlation between the effect of H(2)O(2) on plant growth and the decreases in ABA and zeatin riboside (ZR) was observed. The results suggest an interaction among the redox state and plant hormones, orchestrated by H(2)O(2), in the induction of proteins related to plant signalling and development during the early growth of pea seedlings.
Asunto(s)
Germinación/fisiología , Peróxido de Hidrógeno/metabolismo , Pisum sativum/crecimiento & desarrollo , Reguladores del Crecimiento de las Plantas/metabolismo , Plantones/crecimiento & desarrollo , Ácido Abscísico/farmacología , Ascorbato Peroxidasas , Ácido Ascórbico/metabolismo , Oscuridad , Electroforesis en Gel Bidimensional , Germinación/efectos de los fármacos , Glutatión/metabolismo , Peróxido de Hidrógeno/farmacología , Pisum sativum/efectos de los fármacos , Pisum sativum/enzimología , Peroxidasas/metabolismo , Proteínas de Plantas/metabolismo , Plantones/efectos de los fármacos , Plantones/enzimologíaRESUMEN
ABSTRACT This study reports the combination of a transgene-mediated defense mechanism with a conventionally bred resistance in order to improve apple scab resistance. Two cultivars of apple (Galaxy, scab-susceptible, and Ariane, carrying the Vf resistance gene) were transformed with endochitinase and exochitinase genes derived from the biocontrol fungus Trichoderma atroviride. The obtained transgenic lines were analyzed for the expression of both genes and resistance to two races of the pathogen Venturia inaequalis: the common race 1 and race 6 which overcomes the resistance conferred by the Vf gene. A negative correlation between growth of transgenic lines and endochitinase activity was observed. Reduced growth appeared to be associated with high lignin content and high peroxidase as well as glucanase activity, suggesting that endochitinase activity may disturb the metabolism of the plant. Scab inoculation with races 1 and 6 performed in a growth chamber on 14 lines of normal vigor identified 6 lines with significantly enhanced resistance. Ten lines with reduced vigor were tested in vitro with a bioassay on rooted shoots. All lines expressing high endochitinase activity exhibited a significant reduction of scab symptoms.