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The respiration of fresh potato ( Solanum tuberosum, var. Russet Burbank) slices is predominantly cyanide-sensitive whether in the presence or absence of uncoupler. By contrast, the wound-induced respiration which develops in thin slices with aging is cyanide-resistant, and in the presence of cyanide, sensitive to chlorobenzhydroxamic acid, a selective inhibitor of the cyanide-resistant respiration. Titration of the alternate path in coupled slices with chlorobenzhydroxamic acid, in the presence and absence of cyanide, shows that the contribution of the cyanide-resistant pathway to the wound-induced respiration is zero. Similar titrations with uncoupled slices reveal that the alternate path is engaged and utilized extensively.The maximal capacity of the cytochrome path (V,yt) has been estimated in fresh and aged slices in the presence of the uncoupler carbonyl-cyanide m-chlorophenyl hydrazone. It has been found that V,yt of aged slices is but 30 to 40% higher than that of fresh slices. The results suggest that the bulk of the wound-induced respiration is mediated through the cytochrome pathway which exists in fresh slices in suppressed form, and which is fully expressed by slice aging. The engagement of the alternate path by uncouplers in aged slices is attributed to an increase in substrate moblization, with the result that the electron transport capacity of the cytochrome chain is exceeded.The respiration rate of thin potato slices immediately following cutting is four to five times that of the intact tuber. In the subsequent 24 hr the respiration rises another 4-to 5-fold to yield the wound-induced respiration. Thus, the respiration of aged slices may be 25 times that of the intact tuber (18,32). Slice aging in potato is characterized by two main metabolic transitions. First, whereas tuber and aged slice respiration entails carbohydrate metabolism by way of glycolysis, the pentose-P pathway and the TCAC,3 fresh slices utilize fatty acids as substrate and show little or no TCAC activity (18). Second, slice respiration becomes CNinsensitive with aging (10), and tuber respiration in response to CN progresses from resistant to stimulated (11,29). By contrast, fresh slice respiration is predominantly CN-sensitive (10).Attempts to correlate the respiratory rise which accompanies slice aging with an increase in specific glycolytic or respiratory enzyme activities have not been successful (16,33). On the other hand, it has been shown that the control of phospholipid biosynthesis determines the development of the wound-induced respiration (33, 34). These observations implicate membrane biosyn-

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A cDNA library was constructed from poly(A)(+)RNA of ripe avocado fruit. Colony hybridization identified a number of ripening specific clones of which one, pAV5, was shown to be specific for cellulase. Hybrid selection with pAV5 provided a message from ripe fruit that on in vitro translation yielded a polypeptide of 53kD, comigrating with purified avocado cellulase on SDS polyacrylamide gel electrophoresis. The translation product was selectively immunoprecipitated by antiserum to purified avocado cellulase. Immunoblotting of unripe and ripe avocado fruit extracts following SDS-PAGE showed a plentiful immunoreactive polypeptide in ripe fruit, and essentially none in unripe fruit. Hybridization of pAV5 to poly(A)(+)-RNA from unripe and ripe avocado fruit demonstrated that there is at least a 50-fold increase in the cellulase message concentration during ripening. Thus, the expression of cellulase enzyme activity during ripening is regulated by the appearance of mRNA coding for cellulase rather than by either translational or post-translational control mechanisms.

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