PEROXIDASES IN THE SEPARATION ZONE DURING ETHYLENE-INDUCED BEAN LEAF ABSCISSION

To determine if peroxidase activity is induced specifically in the abscission zone during ethylene-induced cell separation, the spectrum of isoenzymes and activity of the enzyme in extracts from the distal pulvinus, the pulvinus:petiole abscission zone and the petiole of Phaseolus vulgaris leaves were compared. For the cationic isoenzymes, the onset of ethylene-induced cell separation correlated with an increase in the expression of two isoenzymes that are present in both the pulvinus and the abscission zone. In terms of the anionic isoenzymes, two isoenzymes were induced at the time of ethylene-induced cell separation. Both of these are expressed preferentially in the zone, while another was induced predominantly in the petiole. No peroxidase isoenzymes could be detected that were induced specifically in the abscission zone at the time of pulvinus separation. When total enzyme activity was compared, ethylene treatment increased the measurable activity in all tissues, although the highest was at the zone at the time of cell separation. When specific activity was compared, these differences were not as marked. Together, these results show that while peroxidase activity is induced at the abscission zone during ethylene-induced cell separation, changes in specific isoenzymes are observed both in the zone and in neighbouring (non-abscission) tissue. These changes in the spectrum of isoenzymes observed in neighbouring tissue, therefore, should not be ignored when postulating a role for peroxidase in mediating cell-cell separation at the abscission zone.