Immunocytochemical localization of patatin, the major glycoprotein in potato (Solanum tuberosum L.) tubers.

Patatin is a family of glycoproteins with an apparent molecular weight of 40 kDa. The protein is synthesized as a pre-protein with a hydrophobic signal sequence of 23 amino acids. Using different immunocytochemical methods we determined the tissue-specific as well as subcellular localization of the patatin protein. Since antibodies raised against patatin showed crossreactivity with glycans of other glycoproteins, antibodies specific for the protein portion of the glycoprotein were purified. Using these antibodies for electron-microscopical immunocytochemistry, the protein was found to be localized mainly in the vacuoles of both tubers and leaves of potatoes (Solanum tuberosum L.) induced for patatin expression. Neither cell walls nor the intercellular space contained detectable levels of patatin protein. Concerning the tissue specificity, patatin was mainly found in parenchyma cells of potato tubers. The same distribution was observed for the esterase activity in potato tubers.