LOW OXYGEN AND FRUIT RIPENING

In this report we present data concerning the determination of the apparent K_m for oxygen of such overt physiological processes as respiration, timing of the onset of the climacteric, and action of ethylene in "Gala" apples, as well as the effect of 2.5% oxygen on the expression of the cellulase gene in ripening avocados. The results indicate that the affinity for oxygen of these physiological processes differs greatly, respiration having the highest, and the timing of the onset of the climacteric rise in ethylene evolution the lowest. In addition, 2.5% oxygen prevented the rise in total cellulase protein and its mRNA during ripening of avocado fruits. Addition of ethylene to 2.5% oxygen partially restored the suppressive effect of the oxygen on the expression of the cellulase gene. These data are taken to indicate firstly that 2.5% oxygen prevents the synthesis of cellulase at the level of transcription, and secondly that it interferes with the action of ethylene.