ISHS Acta Horticulturae 367: VI International Symposium on Pear Growing
POLYAMINES AND ETHYLENE BIOSYNTHESIS ENZYMES IN PEAR FRUITS: CHANGES IN S-ADENOSYL METHIONINE DECARBOXYLASE AND ACC SYNTHASE ACTIVITIES IN CHILLING SATISFIED RIPENING PACKHAM'S TRIUMPH PEAR FRUITS. |
| Authors: | A. Toumadje, Daryl G. Richardson |
| Abstract:
S-adenosyl methionine (SAM) is the key branch-point intermediate in the biochemical pathways leading to either polyamines or to ethylene. This basically represents a biochemical crossroads where continued polyamine synthesis leads toward non-senescent processes and the ethylene pathway constitutes a shift toward senescent processes, including ripening. We attempted to evaluate this shift at a stage of fruit development when both pathways might be operating, that is, at a time of biochemical transition. Labelled 1-14COOH S-adenosylmethionine was applied to enzyme extracts from Packham's Triumph pears when chilling had just been satisfied (77 days at -1 C) and the flux through the polyamine and ethylene pathways were followed by radioactive precursors during ripening at 20 C. Initially SAM-decarboxylase activity was high, then declined as ACC-synthase activity began to increase to a high level after 3 days, showing the maximal difference on the 5th day, which coincided with maximal ethylene production. Ethylene is well known to stimulate a wide range of senescent processes, including maturation and ripening of climacteric fruits. Conversely, polyamines have been shown to behave as anti-senescent compounds in both leaves and fruits. Interestingly, ethylene and polyamines share S-adenosylmethionine (SAM) as a branch point intermediate compound. We hypothesized that the best developmental stage to try to assess the shift from polyamine synthesis to ethylene synthesis would be when chilling satisfaction is just completed. | |
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