SYNTHESIS OF THE MAJOR POTATO TUBER PROTEINS AND THEIR RELATIONSHIP TO TUBERIZATION

To determine if axillary leaf bud tubers can be used to study tuber protein synthesis in potato we have compared the proteins in axillary bud tubers with those in underground stolon tubers in the variety Superior. By SDS polyacrylamide gel electrophoresis and by electrophoresis in nondenaturing polyacrylamide gels at pH 8.6, the proteins in axillary bud tubers appear to be the same as those in underground stolon tubers. The proteins also appear to be immunologically identical based on Ouchterlony double immunodiffusion test and immunoelectrophoresis. A family of immunologically identical glycoproteins with apparent molecular weights of approximately 40,000 are among the major tuber proteins of potato (Solanum tuberosum L.). These proteins, as purified by ion-exchange and affinity chromatography have been given the trivial name patatin . To determine if patatin can be used as a biochemical marker to study the process of tuberization we have measured its amount in a variety of tissues by rocket immunoelectrophoresis and by enzyme-linked immunosorbent assay (ELISA). Patatin comprises 40-45% of the soluble protein in tubers regardless of whether they are formed on underground stolons or from axillary buds of stem cuttings. Under normal conditions patatin is present in only trace amounts, if at all, in leaves, stems, or roots of plants which are either actively forming tubers or which have been grown under long days to prevent tuberization. However, if tubers and axillary buds are removed, patatin can accumulate in stems and petioles. This accumulation occurred without any obvious tuber-like swelling and would occur even under long days. In all tissues containing large amounts of patatin we also found the other tuber proteins as well as large amounts of starch. By using fluorescent antibody technique it was demonstrated that patatin is preferentially associated with the periphery of starch granules and periphery of cells. This association only occurred in cells which contained storage starch such as tuber cells or petiole cells which have been induced to accumulate starch. Patatin was not found in normal petiole cells