Preliminary characterization of race-specific elicitors fromPeronospora parasitica and their ability to elicit phenolic accumulation inArabidopsis

Abstract

Intercellular washing fluid (IWF) obtained from the susceptibleArabidopsis accession Ws-eds1 inoculated withPeronospora parasitica isolate Emoy-2, contained an elicitor of necrosis with ecotype specificity towardsArabidopsis accessions with particular resistance genes. This elicitor caused necrosis on the highly resistant accessions La-er, Nd-1 and partly on Col-5, but not on the susceptible accessions Ws-eds1 and Oy-0. In resistant plants, injection of IWF caused hypersensitive reaction (HR)-like cell collapse which was associated with the accumulation of phenolics and lignin-like material in walls of cells undergoing cell death. The elicitor is sensitive to proteinase K and pronase enzymes, heating and autoclaving but insensitive to periodate oxidation, freezing and thawing, and is not dialyzable. Results suggest that the elicitor is a protein. Fractionation experiments using size-exclusion membranes revealed that elicitor activity has a molecular weight in excess of 100 kDa.