Effects of Ethylene and 2,4‐D on the Activity of Cellulase Isoenzymes in Abscission Zones of the Developing Orange Fruit

The role of ethylene and 2,4‐D in the abscission process, and the induction of cellulase isoenzymes in the abscission zones of Citrus fruit at two physiological stages of fruit development, were studied using a new staining technique for the detection of cellulase isoenzymes in polyacrylamide gels following electrophoretic separation. Four to seven isoenzymes were detected in the shoot‐peduncle (zone A) and peduncle‐fruit (zone C) abscission zones; at least two of them could be detected at excision time, and of these at least one could not be connected with abscission. In the young fruit, ethylene enhanced and 2,4‐D delayed both abscission and the formation of several isoenzymes. In the older fruit, ethylene enhanced and 2,4‐D delayed the formation of isoenzymes at a time where no abscission occurred any more in zone A. A slower but significant increase in most of the isoenzyme activity detected was also observed in abscission zone A of untreated older fruit explants after excision. These results fully agree with those reported earlier in relation to total cellulase and polygalacturonase activity (Greenberg et al., Physiol. Plant. 34: 1, 1975) tested at the same stages of fruit development. It is suggested, that the generality of the concept that a rise in hydrolytic enzymes in the abscission zone is necessarily followed by separation of the organ should be re‐evaluated.