Isolation and Characterization of a Proteinaceous Inhibitor of Microbial Proteinases Induced During the Hypersensitive Reaction of Tobacco to Tobacco Mosaic Virus. P. Geoffroy. Institut de Biologie Moléculaire des Plantes du CNRS, Université Louis Pasteur, 67000 Strasbourg, France. M. Legrand, and B. Fritig. Institut de Biologie Moléculaire des Plantes du CNRS, Université Louis Pasteur, 67000 Strasbourg, France. MPMI 3:327-333. Accepted 17 May 1990. Copyright 1990 The American Phytopathological Society.

A proteinase inhibitor is strongly induced in tobacco leaves reacting hypersensitively to tobacco mosaic virus. The tobacco inhibitor is highly active against four different serine endoproteinases of fungal and bacterial origin (EC 3.4.21.14) but inhibits poorly two serine endoproteinases of animal origin, trypsin (EC 3.4.21.4) and chymotrypsin (EC 3.4.21.1). The inhibitor has been purified to homogeneity by successive steps of conventional and high-performance liquid chromatography. When electrophoresed under denaturing conditions, it behaves as a small polypeptide with a molecular weight of about 6,000. From its amino acid composition and NH₂-terminal amino acid sequence analysis, it appears that the inhibitor belongs to the potato inhibitor I family. A polyclonal antiserum was raised against the purified tobacco inhibitor and was used in immuno-blotting experiments to follow inhibitor accumulation during the hypersensitive reaction of tobacco to tobacco mosaic virus. The inhibitor is highly efficient and might represent a potent fungicide and/or bactericide to be used in plant biotechnology.