Cellulase and Abscission in the Red Kidney Bean (Phaseolus vulgaris)

Cellulase (β-1, 4-glucan-glucanohydrolase EC 3.2.1.4) activity in the abscission zone of red kidney bean (Phaseolus vulgaris) was previously shown to exist in at least two different molecular forms. The form of the enzyme which has an isoelectric point of 4.5 is present in both abscising and nonabscising tissue and requires grinding for extraction. Another form of the enzyme which has an isoelectric point of 9.5 is present only in tissue in which the abscission process has been induced. Further, much of this form of cellulase can be removed from the tissue by vacuum infiltration with buffer. Time course studies indicate that while the increase in measurable cellulase activity in tissue which is actively undergoing abscission was due primarily to the appearance of cellulase 9.5, this form of the enzyme cannot be removed by vacuum infiltration until after the breakstrength of the abscission zone has decreased nearly to zero. The intracellular localization of these two forms of cellulase is discussed.