In recent years the increase in infestation of trees by pathogens has been reported. In polish forests oak powdery mildew is most commonly caused by a species of fungus Erysiphe alphitoides. Fungi which cause powdery mildew belong to the subdivision Ascomycetes (Ascomycotina). Oak powdery mildew is responsible for significant damage in nurseries.
The development of the infection caused by the fungus Erysiphe alphitoides in cells of oak leaves triggers many processes which involve enzymes and non-enzymatic compounds. One of the first reactions at the beginning of the infection is generation of excessive amounts of reactive oxygen species (ROS). Generation of ROS, often called oxidative burst, can lead to irreversible changes in cell structures and molecules, for example by oxidation of protein thiol groups. The plant features enzymatic of repair systems reducing excessive amounts of ROS. Catalase, per-oxidase and enzymes which are involved in ascorbate-glutathione cycle belong to the defense system.
The aim of the study was to determine the selected antioxidant enzyme activities including peroxidase (POX) and catalase (CAT), elements of ascorbate-glutathione cycle such as ascorbate peroxidase activity (APX) and dehydroascorbate reductase activity (DHAR) and the concentrations of ascorbate (AA) and dehydroascorbate (DHA) in the Quercus robur leaves infected with powdery mildew. Additionally the lignin decomposition as an extra mechanical barrier against pathogen attack was visualised by confocal microscopy.
As material to invastigation one-year-old seedlings of pedunculate oak were obtained, in three times long period, from container nursery of the Forest District Gidle, Poland. For analysis we used leaves with different size of infection area (<5%, 12-15%, 25%).
The results showed the changes in the APX and DHAR activity and in AA and DHA concentrations after pathogen infection which is associated with regeneration of the reduced form of ascorbate. The high activities of antioxidant enzymes in powdery mildew-infected leaves may indicate activation of additional mechanisms that protect cells from oxidative stress.
Keywords: antioxidant enzymes, oak powdery mildew, biotrophic pathogen
Authors
Skwarek M.
Department of Plant Physiology and Biochemistry, University of Lodz, Lodz
Witczak A.
Department of Forest Protection and Ecology, Warsaw University of Life Science – SGGW, Warsaw
Patykowski J.
Department of Plant Physiology and Biochemistry, University of Lodz, Lodz
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