AN ELICITOR FROM PYRICULARIA-ORYZAE INDUCES RESISTANCE RESPONSES IN RICE - ISOLATION, CHARACTERIZATION AND PHYSIOLOGICAL-PROPERTIES

Resistance of rice to the blast fungus, Pyricularia oryzae, has been c orrelated with a range of physiological changes in the infected host t issue. Some of these resistance responses can be induced artificially by elicitors, including chitin and crude extracts from the fungus. Her e, we report on the isolation of a single elicitor species from P. ory zae and on its purification to apparent homogeneity. The elicitor is a glycoprotein with a moi. wt of 15.6 kDa as indicated after SDS-polyac rylamide gel electrophoresis and carbohydrate specific labelling. Acti vity of the water-soluble elicitor is not affected by enzymatic digest ion of the protein core, but is completely abolished after periodate t reatment. The carbohydrate moiety which has no affinity to Con A consi sts mainly of mannose with some glucose and galactose. After applicati on to rice leaves, enhanced activities of enzymes involved in lignific ation were observed. Injection into intercellular spaces of the leaves resulted in increased autofluorescence of cell wails, presumably due to the deposition of lignin or lignin-like substances. When injected i nto the intercellular spaces of genetically susceptible rice leaves pr ior to inoculation with a virulent race of the fungus, the elicitor en abled the plant to successfully defend itself against the pathogen. In these leaves fungal growth was restricted by active host responses si milar to those observed in generically resistant plants. The results s uggest that the isolated elicitor may be involved in the recognition p rocess during the natural infection of rice by P, oryzae. It appears t hat protection is achieved by enhanced sensitivity of recognition or b y promoting a faster and/or more intense host response.