STUDIES ON OILSEED RAPE-PATHOGEN INTERACTIONS
G GRANER1, E ANDREASSON1, M HAMBERG1, L RASK2 and J MEIJER3
1Department of Plant Biology, Uppsala Genetic Center, SLU, SE-750 07 Uppsala, Sweden; 2Department of Medical Biochemistry and Biophysics, Karolinska Institute, Stockholm, Sweden; 3Department of Medical and Physiological Chemistry, Biomedical Center, Uppsala University, SE-751 23 Uppsala, Sweden
Background and objectives
Great interest in understanding the stress response at a molecular level and, in a longer perspective, in improving the stress resistance of plants, has emerged during recent years. Our aim is to characterize the pathogen response of oilseed rape (Brassica napus) on the molecular and cellular levels, with an emphasis on describing components involved in systemic acquired resistance (SAR). We are especially interested in the role of the myrosinase-glucosinolate system  and oxylipins  as antipathogenic agents. We are therefore analysing the response reactions of oilseed rape to different fungi and the potential fungicidic action of oxylipins.
Materials and methods
Pathogens were applied on fully expanded cotyledons of oilseed rape about 10 days after germination. Plants were harvested at different time points and processed for Northern and Western blot analysis or immunocytochemical analysis. The toxicity of different oxylipins was measured as growth inhibition for pathogens grown on potato dextrose agar plates at room temperature in the dark. The oxylipins were applied to the growing fungi and growth inhibition was estimated over 4 days.
Results and conclusions
An interesting discovery was local induction of myrosinase at the site of fungal infection of Phoma lingam. We are at present extending these studies and analysing other pathogens for their effects on the myrosinase system and potential induction of SAR and its characteristics in oilseed rape. In the case of oxylipins, three types of responses were found: virtually no inhibition; inhibition mainly for the first 24 h; and inhibition lasting at least 92 h. For example, Alternaria brassicae and Verticillium dahlie overcome this after 24 h. A hydroperoxy fatty acid was inhibitory for all three pathogens, but only for 24 h. Whether the transient inhibition is dependent on compound instability, metabolism, or other factors of the pathogen remains to be clarified. These results open up the possibility of using endogenous factors as plant protectors.
This study was supported by the Swedish Research Council for Forestry and Agriculture and Foundation for Strategic Research.
1. Bones AM, Rossiter JT, 1996. Physiologia Plantarum 97, 194-208.
2. Hamberg M, 1993. Journal of Lipid Mediators 6, 375-384.