Defense systems against oxidative stresses in two rice cultivars (Oryza sativa L.) with differential tolerance to aluminum / Sistemas de defesa contra estresses oxidativos em dois cultivares de arroz (Oryza sativa L.) com tolerância diferencial ao alumínio

AUTOR(ES)

Cleberson Ribeiro

DATA DE PUBLICAÇÃO

2007

RESUMO

Aluminum (Al) effects on the growth and enzymatic and non-enzymatic antioxidative mechanisms involved in the scavenging of reactive oxygen species (ROIs) in two rice cultivars: Fernandes (CNA-1158) and Maravilha (CNA-6843-1) with differential tolerance to Al were studied. The plants, grown in pH 4.0 nutrient solution, for ten days in nutrient solution, pH 4,0, were treated with Al 0 and 1 mM for ten days. Exposure to Al did not affect growth in Fernandes cultivar, while in Maravilha cultivar significant reductions were observed in the evaluated growth parameters. Aluminum increased the activities of the enzymes, catalases (CATs), peroxidases (POXs), glutathione reductases (GRs) and glutathione peroxidases (GPXs) in the roots of both cultivars. The activity of superoxide dismutases (SODs), however, increased only in the roots of the Fernandes cultivar, while in Maravilha cultivar it remained unchanged. Independent of the applied treatment and of the plant analyzed, the activity of the ascorbate peroxidases (APXs) was always larger in Fernandes cultivar. In the leaves, Al did not change any enzyme activity in Fernandes cultivar, except the POXs activity which reduced. In Maravilha cultivar, on the other hand, SODs, POXs and GPXs activities reduced in the presence of Al. Among the studied enzymes, SODs, APXs and GPXs in the roots and of CATs, POXs and APXs in the leaves, showed responses to Al treatment consistent with the differential tolerance to Al of these two rice cultivars. Ascorbate (AA) contents increased in the leaves and dehydroascorbate (DHA) decreased in the roots, in response to the Al treatment in both cultivars. The reduced form (AA) content was much higher in the leaves, where the AA/DHA ratio reached values thirty times larger times than in the roots. In the roots, Fernandes cultivar showed lower AA contents, but higher APXs activity and the Maravilha cultivar the opposite, indicating an important role of this metabolite as substrate for the reaction catalyzed by APXs. Total glutathione contents, also, seem be important to the non-enzymatic defense system of both cultivars, but probably will be necessary to discriminate between reduced (GSH) and oxidized (GSSG) form to understand the role of this substance in sustaining antioxidative enzyme activities. In general, the activity of the antioxidative system, enzymatic and non-enzymatic, both in roots and leaves, were suggestive of having Fernandes cultivar a more efficient defense mechanism to the ROIs produced by Al treatments.

ASSUNTO(S)

tolerance to aluminum oxidative stresses tolerância ao alumínio rice arroz enzimas antioxidativas estresse oxidativo antioxidative enzymes fisiologia vegetal

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