Conjugated polyamine levels and putrescine synthesis in cherimoya fruit during storage at different temperatures

In a previous study (J. Plant Physiol. 143, 207-212, 1994) we reported a rise in free putrescine levels in cherimoya fruit (Annona cherimola Mill.) during ripening. In an attempt to explain such an increase, conjugated polyamine levels, arginine decarboxylase (ADC, EC 4.1.1.19) and ornithine decarboxylase (ODC, EC 4.1.1.17) activities were determined in cherimoya fruit stored at 20, 10, 8 and 6 degrees C. No PCA-insoluble conjugated spermine and PCA-soluble conjugated putrescine titers were detected at any temperature or time interval. PCA-soluble conjugated spermine titers were observed to decline early on in the low-temperature storage period. While PCA-insoluble conjugated spermidine content grew steadily in fruit kept at 20 degrees C, it was found to decrease throughout the storage period in fruit at lower temperatures. While PCA-insoluble conjugated putrescine levels increased in ripe fruit, they were nonetheless substantially lower than the free-form levels. The rise in putrescine levels in ripening cherimoya fruit was correlated with greatly enhanced ADC activity. No ODC activity was detected under any of the experimental conditions. It is suggested that the ripening-related changes in putrescine levels are regulated via ADC-activity-mediated synthesis and that no conjugation is involved in the process.