Sistemas de defesa contra estresses oxidativos em dois cultivares de arroz (Oryza sativa L.) com tolerância diferencial ao alumínio
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2007-03-08
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Universidade Federal de Viçosa
Resumo
Os efeitos do alumínio (Al) sobre o crescimento e sobre os sistemas de defesa antioxidativos enzimáticos e não-enzimáticos envolvidos na eliminação dos intermediários reativos de oxigênio (ROIs) foram avaliados em dois cultivares de arroz: Fernandes (CNA-1158) e Maravilha (CNA-6843-1) com tolerância diferencial ao Al. As plantas, cultivadas em solução nutritiva, pH 4,0, foram tratadas com Al nas concentrações de 0 e 1 mM, durante dez dias. A exposição das plantas ao Al não afetou o crescimento no cultivar Fernandes, enquanto, no Maravilha, reduções significativas foram observadas nos parâmetros de crescimento avaliados. Nas raízes dos dois cultivares, a presença do Al aumentou a atividade das enzimas catalases (CATs), peroxidases (POXs), redutases da glutationa (GRs) e peroxidases da glutationa (GPXs). A atividade das superóxido dismutases (SODs) aumentou apenas nas raízes do cultivar Fernandes, não sendo modificada para o cultivar Maravilha. Independente do tratamento aplicado e da parte da planta analisada, a atividade das peroxidases do ascorbato (APXs) foi sempre maior no cultivar Fernandes. Nas folhas, o Al não alterou a atividade de nenhuma das enzimas no cultivar Fernandes, exceto a das POXs que sofreu redução. No cultivar Maravilha, por outro lado, as atividades das SODs, POXs e GPXs foram reduzidas na presença de Al. Dentre as enzimas estudadas, as SODs, APXs e GPXs nas raízes e as CATs, POXs, APXs nas folhas, exibiram resposta consistente com a tolerância diferencial ao Al apresentada pelos dois cultivares de arroz estudados. Nos dois cultivares, o teor de ascorbato (AA) aumentou nas folhas e o de desidroascorbato (DHA) reduziu nas raízes, em resposta ao tratamento com Al. O teor da forma reduzida (AA) foi muito mais elevado nas folhas, na qual a relação AA/DHA atingiu valores 30 vezes maiores que nas raízes. Nas raízes, o cultivar Fernandes apresentou menores teores de AA, porém maior atividade das APXs, enquanto no cultivar Maravilha foi observado o oposto, demonstrando o importante papel desse metabólito como substrato para a reação catalisada pelas APXs. A concentração de glutationa total, também, parece ser importante no sistema de defesa não enzimático, mas provavelmente seria necessário discriminar entre as suas formas, reduzida (GSH) e oxidada (GSSG), para entender seu papel como substrato das enzimas antioxidativas. De modo geral, as atividades dos sistemas de defesa antioxidativos enzimático e não-enzimático, tanto nas raízes como nas folhas dos dois cultivares, indicaram ter o cultivar Fernandes mecanismos de defesa mais eficientes no combate aos ROIs produzidos durante o tratamento com Al.
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.
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.
Descrição
Palavras-chave
Tolerância ao alumínio, Estresse oxidativo, Arroz, Enzimas antioxidativas, Tolerance to aluminum, Oxidative stresses, Rice, Antioxidative enzymes
Citação
RIBEIRO, Cleberson. Defense systems against oxidative stresses in two rice cultivars (Oryza sativa L.) with differential tolerance to aluminum. 2007. 61 f. Dissertação (Mestrado em Controle da maturação e senescência em órgãos perecíveis; Fisiologia molecular de plantas superiores) - Universidade Federal de Viçosa, Viçosa, 2007.