Phytoalexin induction and beta-1,3-glucanase activities in Colletotrichum trifolii infected leaves of alfalfa (Medicago sativa L.)

摘要

Defence responses were measured in leaves of alfalfa (Medicago saliva L.) after infection by virulent (compatible) and avirulent (incompatible) races of the anthracnose fungus Colletotrichum trifolii. In the incompatible interaction, the isoflavonoid phytoalexin medicarpin and its conjugates started to accumulate 24 and 48 h after inoculation, respectively, whereas their appearance was delayed to 48 and 72 h, respectively, in the compatible interaction. No differences in the activities of beta-1,3-glucanase isoforms were detected between infected and mock-inoculated tissues; expression of these defence-related hydrolases was constitutive. Constitutive overexpression of the alfalfa acidic glucanase Aglu 1 in Regen SY, an alfalfa cultivar susceptible to C. trifolii, did not result in a greater or more rapid phytoalexin response, nor did it reduce the symptoms following pathogen attack, even though the majority of transgenic plants expressing the aglu 1 transgene produced other glucanase isoforms that were not expressed in the non-transformed plants. The results do not support the hypothesis that glucanases may function in host defence to release elicitors of the phytoalexin response in the alfalfa/C. Irifolii interaction.