Ethylene biosynthesis in 'Bartlett' and 'd'Anjou' pears (Pyrus communis L.), cultivars that differ in their ripening requirements

Ethylene levels and the activities of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase were compared in 'd'Anjou' and 'Bartlett' pears, cultivars that differ in their chilling requirements for ripening. 'd'Anjou' pears require chilling prior to ripening while 'Bartlett' pears do not. The last step of ethylene biosynthesis is catalyzed by ACC oxidase. Ethylene production, enzyme activity and ACC oxidase mRNA accumulated during chilling of 'd'Anjou' pears, a cultivar that requires 1-2 months of cold storage to ripen. Ethylene, ACC oxidase enzyme activity and ACC oxidase mRNA rose analogously in 'Bartlett' pears but without a chilling treatment. The chilling requirement of 'd'Anjou' pear was bypassed by treatment with ethephon, an ethylene-releasing chemical. ACC oxidase activity and ACC oxidase mRNA were rapidly induced by ethephon application. Placement of preclimacteric 'Bartlett' and 'd'Anjou' in controlled atmosphere storage (2{dollar}spcirc{dollar}C, 1% oxygen) severely reduced the production of ethylene, ACC oxidase activity and ACC oxidase mRNA. These data show that ethylene and ACC oxidase in both pear cultivars were similarly inhibited by low oxygen but were stimulated by chilling in 'd'Anjou' and developmentally regulated in 'Bartlett'.; Preliminary experiments on the regulation of ACC synthase in 'd'Anjou' and 'Bartlett' pears were also completed. ACC synthase mRNA was present in both preclimacteric 'Bartlett' and 'd'Anjou' fruit and levels remained fairly constant regardless of chilling treatment, advancing maturity or low oxygen treatment. ACC synthase enzyme activity increased slightly in 'd'Anjou' after 2 months of cold storage and rose dramatically in 'Bartlett' after a chilling treatment and subsequent rewarming period. ACC synthase enzyme activity was suppressed in 'Bartlett' pears by low oxygen storage. These results suggest that ACC synthase in 'Bartlett' pears is regulated primarily at the enzyme level.; 2,5-Norbornadiene was added to the atmosphere surrounding chilling-satisfied 'd'Anjou' pears in an attempt to inhibit ethylene action. After short or extended treatment, ethylene production rates of the treated fruit were much higher than the controls, suggesting that the applied concentrations of 2,5-norbornadiene may have been toxic to the pears.; A reliable RNA extraction method for pear fruit tissue was also developed.