| Studies were performed to determine changes in firmness, cell-wall polyuronides, gene expression; and the activities of cell-wall and membrane hydrolases, and ethylene biosynthetic enzymes in intact and fresh-cut papaya fruit during storage at 5°C. Significantly higher polyuronide solubility and depolymerization and firmness decreases were observed in fresh-cut fruit as compared with intact fruit during storage. Activities of polygalacturonase, alpha- and beta-galactosidases, lipoxygenase, phospholipase D, and ACC synthase and ACC oxidase increased in fresh-cut fruit, and remained significantly higher than in intact fruit throughout the storage period. Differential display analysis performed on fruit stored for 12 hours resulted in identification of 98 genes differentially expressed in response to fresh-cut processing. The differentially expressed cDNAs, PC18-1, PC17, PC23, PA17, PC18-2, PC18-3, PG23, PC18-4, PA19-3 and PG17 showed significant homologies to mitogen- and stress-activated protein kinases, the A kinase anchor protein 2, CAAX prenyl protease, lipoxygenase, membrane channel protein, superoxide dismutase, ACC synthase 2, Homo sapiens BAC clone GSI-195F7, calmodulin and beta galactosidases, respectively. The partial cDNA clones PA19-1, PA22, PC 18-4 and PA 19-2 showed no significant homology to any known sequences in the database. Northern blot analysis showed high levels of the expression for most of the clones in the fresh-cut papaya fruit during storage. Data suggest that changes in cell walls and membranes due to increased hydrolase activity contribute to the rapid deterioration of fresh-cut fruit.; Watermelon fruit exhibits acute symptoms of whole-fruit softening and placental-tissue water-soaking on ethylene exposure. An experiment was conducted to address the firmness, mRNA and activities of cell wall and membrane hydrolases and ethylene biosynthetic enzymes, and solubility and mol mass properties of polyuronides in placental tissue in response to ethylene exposure. Watermelon fruit harvested at the immature and full-ripe stages were exposed to 50 μL L−1 ethylene for 6 days at 20°C. Placental tissue firmness from ethylene-treated ripe and immature fruit decreased nearly 80% during 6 days of ethylene exposure with extensive polyuronide solubility and depolymerization. The levels of mRNA and activities of polygalacturonase, lipoxygenase, phospholipases C and D, and ACC synthase and oxidase elevated on ethylene exposure, suggest that cell-wall and membrane catabolism contribute to the development of water-soaking. |
