Decreased Cellulase Activity in Avocado Fruit Subjected to 2.5% O2 Correlate: with Lower Cellulase Protein and Gene Transcript Levels

Low (2.5%) oxygen atmosphere was previously shown to prevent the normal rise in cellulase activity in avocado fruits primed for ripening by pre-exposure to 10/μl/liter ethylene (Kanellis et al. 1987, Kanellis et al. 1989b). Such primed avocado fruits were used in the present study to determine the effect of 2.5% O<inf>2</inf> atmosphere on the accumulation of cellulase protein and its mRNA using specific antibody and cDNA probes. Decrease in cellulase activity was paralleled by a decrease in immunogenic cellulase protein in fruits held in 2.5% O<inf>2</inf>. Under these conditions only 10-20% of total cellulase gene transcripts were expressed. Inclusion of ethylene in the low O<inf>2</inf> atmosphere did not significantly alter the expression of the cellulase gene. Accumulation of cellulase mRNA during ripening was not due to polyadenylation of pre-existing mRNAs. Thus, low O<inf>2</inf> appears to regulate cellulase gene expression at a pre-translational level.