Localization of Pathogenesis-Related Proteins in the Epidermis and Intercellular Spaces of Tobacco Leaves after Their Induction by Potassium Salicylate or Tobacco Mosaic Virus Infection

Abstract

The localization of pathogenesis-related (PR) proteins induced in tobacco leaves by treatment with potassium salicylate or a hypersensitive response to tobacco mosaic virus (TMV) infection was studied using immunochemical methods. Total PR protein levels increased with time after these treatments. The proportion of PR proteins in the intercellular spaces to the total content in the leaf discs rapidly rose in the later stage of the treatment to about 75% on the 9th day after salicylate treatment and to more than 80% on the 6th to 9th day after TMV inoculation. After 5 days of salicylate treatment, the amounts of PR proteins in the peeled leaf epidermis were two fold those in the mesophyll tissue. Only five percent or less of the total PR proteins in the epidermal and mesophyll tissues of salicylate-treated leaves were detected in the isolated epidermal and mesophyll protoplasts. The sugar content in highly purified PR la, lb and lc was less than one mole of monosaccharide per mole of each protein. These results show that the PR proteins are non-glycoproteins secreted into the intercellular spaces.