PROTEIN MOBILIZATION FROM POTATO TUBERS DURING LONG-TERM STORAGE AND DAUGHTER TUBER FORMATION

The role of protease inhibitors in modulating changes in protein content of potato (Solanum tuberosum L.) tubers was investigated using a mother/daughter tuber model system. Changes in patatin, potato multicystatin (PMC), proteases, serine (Ser) protease inhibitors, and their gene expression were temporally coordinated over a 22-mo storage interval in genotypes with short (cv. Ranger Russet) and long (cv. Russet Burbank) dormancy. Daughter tubers were initiated on Ranger Russet tubers at similar to 15 mo. PMC (Cys protease inhibitor) declined linearly (similar to 4.2-fold) in Ranger Russet mother tubers from 4 to 15 mo and then maintained low levels through 22 mo. Conversely, protease activity was low and constant from 4 to 15 mo before increasing 7.4-fold through 22 mo. This increase coincided with the most rapid decline (54%) in patatin and the formation of daughter tubers. The proteases induced during aging of mother tubers were inhibited by PMC. Ser protease inhibitors were maintained in mother tubers throughout storage. In contrast, as daughter tubers developed, PMC and Ser protease inhibitors increased, protease activity declined to 17% of initial levels, and patatin increased threefold. These results implicate a role for protease inhibitors in regulating protein content during mobilization from mother tubers and deposition in daughter tubers.