Crescimento, morfologia e mudanças no sistema antioxidativo em raízes de arroz, submetidas ao alumínio

• Autor(a) principal: Ribeiro, Cleberson
• Data de Publicação: 2011
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/983
• topic: Alumínio; Intermediários reativos de oxigênio; Ascorbato; Glutationa; Estresse oxidativo; Arroz; Aluminum; Reactive oxygen intermediates; Ascorbate; Glutathione; Oxidative stress; Rice; CNPQ::CIENCIAS BIOLOGICAS::BOTANICA::FISIOLOGIA VEGETAL

In acid soils, aluminum (Al) toxicity is one of the main factors limiting plant growth and development. The exposure of plants to toxic levels of this element can increase the reactive oxygen species (ROS) production and, consequently, to induce oxidative stress. To avoid excessive accumulation of ROS, plants make use of antioxidative defense systems involving metabolites and several antioxidative enzymes. The present work aimed to evaluate some damages caused by Al on root growth and morphology and on ascorbate/ glutathione system responses in two rice cultivars: Fernandes (CNA-1158) and Maravilha (CNA-6843-1), considered tolerant and sensitive to Al, respectively. Nine days after plant treatment with Al 0 and 1 mM, the effects of Al on root growth and morphology, on ROS, ascorbate (AA), dehydroascorbate (DHA), reduced glutathione (GSH) and oxidized glutathione (GSSG) contents and on the activities of the enzymes superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR), γ-glutamycysteine synthetase (γ- GCS), glutathione S-transferase (GST) monodehydroascorbate reductase (MDHAR) and dehydroascorbate reductase (DHAR) were evaluated. Maravilha cultivar showed higher Al accumulation and lower root growth than Fernandes cultivar. Aluminum accumulated especially in root tips in both cultivars, but the root of Maravilha cultivar became thicker than those of Fernandes cultivar. The accumulation of Al caused structural root damages, with rupture of the cells of the root cap, changing the external morphology of the roots tips in both rice cultivars, mainly in Maravilha cultivar. Fernandes cultivar showed lower ROS content and lower degree of lipid peroxidation than Maravilha cultivar, characterizing its higher tolerance to Al. Fernandes cultivar showed, also, larger activity of the SOD, APX, CAT and POX enzymes and larger regeneration of AA in its roots, indicative of a more efficient mechanism in the elimination of the excess of ROS produced during the oxidative stress caused by Al. The activities of the enzymes γ-GCS and GR, involved with the synthesis and regeneration of the glutathione, respectively, increased in the roots of the Fernandes cultivar, while in Maravilha cultivar only γ-GCS showed an increase in activity in the 9th day of treatment with Al. The activity of GPX increased in the roots of both cultivars treated with Al, but in the Maravilha cultivar Al effect was less intense and occurred later. Fernandes cultivar, in Al presence, was capable to maintain a GSH content and GSH/GSSG ratio higher and, therefore, a better buffer redox than the Maravilha cultivar. Therefore, most of the rice tolerance capacity to tolerate the oxidative stress caused by Al seems to be result of a synchronized operation of enzymatic and non-enzymatic systems associated with the metabolism of ascorbate and glutathione. The antioxidative enzyme activities as well as ascorbate and, or glutathione contents indicate a higher efficiency of the ascorbate/glutathione system in Fernandes cultivar than in Maravilha cultivar.