Abstract
Upon initiation of ripening in avocado fruit (P. americana Mill. cv. Hass) with 10 .mu.l/l ethylene, polysome prevalence and associated poly(A)+ mRNA increase approximately 3-fold early in the respiratory climacteric and drop off preclimacteric levels at the peak of the respiratory climacteric. The increase in poly(A+) mRNA on polysomes early in the respiratory climacteric constitues a generic increase in constitutive mRNA. New gene expression associated with ripening is minimal but evident after 10 h of ethylene treatment and continues to increase relative to constitutive gene expression throughout the climacteric. The respiratory climacteric can be temporally separated into 2 phases. The 1st phase is associated with a general increase in protien synthesis, whereas the 2nd phase reflects new gene expression and accumulation of corresponding protiens which may be responsible for softening and other ripening characteristics. A major new message on polysomes that arises concomitantly with the respiratory climacteric codes for an in vitro translation product of 53 kilodaltons which is immunoprecipitated by antiserum against avocado fruit cellulase. Cyanide at 500 .mu.l/l fails to affect the change in polysome prevalence or new gene expression associated with the ethylene-evoked climacteric in avocado fruit. Treatment of fruit with 500 .mu.l/cyanide alone initiates a respiratory increase within 4 h, ethylene biosynthesis within 18 h, and new gene expression akin to that educed by ethylene within 20 of exposure to cyanide.