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.Abbreviations PHA phytohemagglutinin - TFMS trifluoromethanesulfonic acid     

Patatin,a major soluble protein of the potato (Solanum tuberosum L.) tuber is synthesized as a larger precursor

Antibodies were raised against the highly purified glycoprotein patatin. They were used to characterize the product synthesized in a wheatgerm cell-free translation system, programmed with polyadenylated RNA from potato tubers. Sodium dodecylsulfate-polyacrylamide gel electrophoresis revealed that the immunoprecipitated protein had a molecular mass of 43 kDa compared to 40 for the authentic patatin. It is assumed that patatin is synthesized in vivo as a larger precursor which is processed to the mature protein by cleavage of a signal peptide. Our results are in agreement with sequence-analysis data of patatin complementary DNA which indicate a signal peptide of about 23 amino acids (Mignery et al., 1984; Nucleic Acids Res. 12, 7987–8000).Abbreviation Poly(A)⁺ RNA polyadenylated RNA - SDS-PAGE sodium dodecyl sulfate-polyacrylamide gel electrophoresis Preliminary results were published in Mitteilungsband, Botaniker Tagung in Wien, p. 180, Wien, September 1984     

Factors affecting gene expression of patatin and proteinase-inhibitor-II gene families in detached potato leaves:

In whole intact potato (Solanum tuberosum L.) plants, the gene families of class-I patatin and proteinase inhibitor II (Pin 2) are constitutively expressed in the tubers. However, they are also induced in detached potato leaves in the presence of light. To further characterize this light action, the detached leaves were subjected to monochromatic light of different wavelengths and to darkness in the presence of metabolites and inhibitors. Patatin genes could be induced by the simultaneous application of sucrose (sugars) and glutamine in darkness. Neither of these metabolites was active when supplied alone. When photosynthesis was blocked by 3-(3,4-Di-chlorophenyl)-1, 1-dimethylurea (DCMU) in the light, patatin genes were not expressed; however, the inhibition was overcome in the presence of sucrose. This indicates that besides its role in photosynthetic carbohydrate production, light may be essential for the supply of amino acids (or reduced nitrogen). Unlike patatin, Pin 2 genes were, to a small extent, also active in darkness, and sucrose weakly enhanced this expression. However, DCMU did not affect Pin 2 expression in the light. Both abscisic acid and methyl jasmonate strongly promoted the accumulation of Pin 2 mRNA independent of the light conditions, indicating that the gene family is probably under hormonal control. The phytohormones did not affect patatin gene expression. Inhibitors of cytosolic (cycloheximide) and organellar (chloramphenicol) translation had opposite effects on the two gene families. Careful evaluation of the inhibitors' action indicates that protein synthesis (cytosol) is required for the expression of Pin 2 genes but not for the patatin genes. These results clearly demonstrate that, although in situ both gene families are constitutively expressed in the same plant organ (tuber) in intact plants, their expression is mediated by different factors.Abbreviations ABA cis-abscisic acid - DCMU 3-(3,4-dichlorphenyl)-1,1-dimethylurea - GUS -glucuronidase activity - MeJA methyl jasmonate - Pin 2 proteinase inhibitor II We thank Beate Küsgen and Regina Breitfeld for the greenhouse work. This work was supported by a grant from the Bundesministerium für Forschung und Technologie.