Alterações bioquímicas e fisiológicas em plantas de trigo infectadas por Pyricularia oryzae

• Autor(a) principal: Debona, Daniel
• Data de Publicação: 2012
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4422
• topic: Brusone; Estresse oxidativo; Fontossíntese; Trigo; Blast; Oxidative stress; Photosynthesis; Wheat; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOSSANIDADE::FITOPATOLOGIA

Blast, caused by the fungus Pyricularia oryzae, is the most important disease of wheat in brazilian Cerrado. However, information in the literature about wheat-P. oryzae interaction is still limited. In this study, it was investigated biochemical and physiological changes in wheat plants from cultivars BR 18 and BRS 229, susceptible and partially resistant to blast at young plant stage, respectively, during the infectious process of P. oryzae. The variables studied were: blast severity, activity of antioxidant enzymes and superoxide (O2-), hydrogen peroxide (H2O2) and malondialdehyde (MDA) concentrations, and electrolyte leakage (EL), as well as gas exchange parameters at 48, 72 and 96 hours after inoculation (hai) with P. oryzae. Additionally, it was determined the maximum rate of carboxylation (Vcmax), the maximum rate of electron transport used on ribulose- 1,5-bisphosphate (RUBP) regeneration (Jmax), and respiration (Rd) and calculated the Jmax/Vcmax ratio based on the response of net carbon assimilation rate (A) to different internal CO2 concentration (Ci) (A/Ci curve). The blast severity was lower in plants from cultivar BRS 229 than in plants from cultivar BR 18. The activity of antioxidant enzymes system was strongly affected by infection with P. oryzae and usually higher in inoculated plants than in noninoculated plants. The increase in activity of superoxide dismutase, peroxidase, ascorbate peroxidase and glutathione-S-transferase at 96 hai was more pronounced for cultivar BRS229 than for cultivar BR 18. The activity of glutathione reductase (GR) and catalase (CAT) increased only in inoculated plants from cultivar BRS 229 at 96 hai compared with noninoculated plants. For cultivar BR 18, GR activity was not affected by inoculation with P. oryzae and CAT activity was lower in inoculated plants than in noninoculated plants. The activity of glutathione peroxidase increased in inoculated plants from cultivar BR 18 in relation to noninoculated plants at 48 and 72 hai, and it was not affected by inoculation with P. oryzae on plants from cultivar BRS 229. O2- concentration increased 153 and 72% at 96 hai in inoculated plants from cultivars BR 18 and BRS 229, respectively, compared with noninoculated plants. H2O2 concentration was 59% higher in inoculatedx plants from cultivar BR 18 in relation to noninoculated plants at 96 hai, but there was no difference between inoculated and noninoculated plants for cultivar BRS 229. MDA concentration was higher in inoculated plants at 48, 72, and 96 hai for cultivar BR 18 and just at 48 hai for cultivar BRS 229, in relation to noninoculated plants. EL increased 323 and 188% at 96 hai in inoculated plants from cultivars BR 18 and BRS 229, respectively, compared with noninoculated plants. The gas exchange parameters A, stomatal conductance and transpiration rate as well as Vcmax and Jmax were significantly reduced in inoculated plants from both wheat cultivars compared with noninoculated plants. This reduction, however, was less pronounced in the plants from cultivar BRS 229 than in the plants from cultivar BR 18, which was associated with lower blast severity observed for BRS 229. Ci increased 32 and 14% at 96 hai in inoculated plants from cultivars BR 18 and BRS 229, respectively. The Jmax/Vcmax ratio increased in inoculated plants from both cultivars in relation to noninoculated plants. Rd increased 208% in inoculated plants from cultivar BR 18 in relation to noninoculated plants at 96 hai, but there was no difference in Rd between inoculated and noninoculated plants for cultivar BRS 229. The results of this study demonstrated the importance of an efficient antioxidant system to remove excess of reactive oxygen species generated during infection of wheat plants with P. oryzae limiting the cellular damage caused by the fungus. Additionally, the more efficient antioxidant system appears to contribute to a greater resistance to wheat blast. The physiological evaluations showed that the photosynthesis of wheat plants was significantly reduced by infection with P. oryzae, what was mainly associated with lower apparent activity of Rubisco, followed by the lower RuBP regeneration. Knowledge of biochemical and physiological changes of wheat plants infected with P. oryzae is of great importance to develop effective strategies for control of wheat blast.