The pathogenesis-related proteins of tobacco leaves

Extracts from the leaves of tobacco plants (cv. Xanthi-nc.) which are reacting hypersensitively to infection with TMV contain the four well-known pathogenesis-related proteins (PR-Ia, b, c and II), and in addition other PR-proteins which can be distinguished by electrophoresis and chromatofocussing. These proteins are referred to as N, O, P, Q, R and O′, P′, Q′ and R′ which have electrophoretic mobilitics similar to O, P, Q and R. Four of the proteins have been isolated and characterized in terms of subunits and amino acid composition; R′ contains small amounts of N-acetylglucosamine. None of the proteins appears to have lectin-like properties or to interact with concanavalin A, and only R′ weakly interacts with wheat germ agglutinin. Proteins N-R′, like PRs I and II, are present in appreciable amounts in leaves treated with salicylate and in old leaves from flowering tobacco plants.