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

Abstract

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% O2 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% O2. Under these conditions only 10-20% of total cellulase gene transcripts were expressed. Inclusion of ethylene in the low O2 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 O2 appears to regulate cellulase gene expression at a pre-translational level.