Oxidative, molecular and physiological changes on maize plants infected by Exserohilum turcicum

• Ano de defesa: 2016
• Autor(a) principal: Silveira, Patricia Ricardino da
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: eng
• Instituição de defesa: Universidade Federal de Viçosa
• Palavras-chave em Português: Milho - Doenças e pragas; Exserohilum turcicum; Milho - Fisiologia; Milho - Enzimas; Fitopatologia
• Link de acesso: https://locus.ufv.br//handle/123456789/27455

Northern leaf blight (NLB), caused by the fungus Exserohilum turcicum is a disease of great importance in producing maize areas worldwide and is responsible for significant losses during the occurrence of disease epidemics. The first study aimed to verify the activities of enzymes and genes expression involved in the antioxidative metabolism as well as the concentration of hydrogen peroxide (H 2 O 2 ) and malondialdehyde (MDA) as well as the electrolyte leackage (EL) in maize plants infected and non-infected with E. turcicum. The activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), peroxidase (POX), glutathione reductase (GR), glutathione-S- transferase (GST) and glutathione peroxidase (GPX) increased in infected plants compared to non-infected plants mainly from 10 days after inoculation (dai). The relative expression of the genes coding for superoxide dismutase (sod), catalase (cat), ascorbate peroxidase (apx), peroxidase (pox), glutathione reductase (gr) and glutathione-S-transferase (gst) were higher for the infected plants in comparison to the non-infected ones especially at more advanced stages of fungal infection. The H 2 O 2 and MDA concentrations increased from 15 and 20 dai for the infected plants in comparison to the non-infected ones and the EL increased for the infected plants from 10 dai. In general, there was an increase in the values for all variables obtained from the infected plants mainly at the final stage of fungal which was accompanied by an increase on disease development. In conclusion, a late involvement of the antioxidant metabolism in the infected leaves was not helpful to counteract the deleterious effects of E. turcicum infection at its necrotrophic phase. The second study was carried out to investigate the photosynthetic changes in maize plants infected with E. turcicum. The parameters of leaf gas exchange (net carbon assimilation rate ((A), stomatal conductance (g s ), transpiration rate (E) and internal CO 2 concentration (C i )) and chlorophyll (Chl) a fluorescence (maximum quantum yield of photosystem II (PSII) (F v /F m ), effective quantum yield of photosystem II (PSII) ((Y(II)), quantum yield of regulated energy dissipation ((Y(NPQ)), quantum yield of non-regulated energy dissipation ((Y(NO)) and electron transport rate (ETR)) were evaluated as well as the concentrations of photosynthetic pigments Chl a , Chl b and carotenoids. The values of A, g s , E and C i decreased as the symptoms of NLB developed. Changes in Chl a fluorescence parameters became evident at 10 days after inoculation (dai) and changes in the images began from 5 dai and intensified at advanced stages of fungal infection. The concentrations of Chl a , Chl b and carotenoids decreased in the leaves of infected plants at 15 and 20 dai. In conclusion, the results from the present study demonstrate, for the first time, that the photosynthesis on the leaves of maize plants was dramatically affected during the infection of process of E. turcicum mainly through limitations of diffusive and biochemical nature