Role of Cellulase in Abscission of Citrus Fruits1

Abstract

The concept of cellulolytic enzymes being involved in abscission has been confirmed and extended in this study to include the fruits of ‘Calamondin’ (Citrus madurensis Lour.) and ‘Valencia’ sweet orange [C. sinensis (L.) Osbeck]. Data have been presented which demonstrate that an increase in cellulase activity is associated with natural and chemically accelerated abscission of citrus fruits. Ethylene, the most effective accelerant of abscission studied, shortened the time for attainment of measurable increases in cellulase activity preceding separation and shortened the time between detectable increases in cellulase activity and attainment of high cellulase activity. Pectinase did not seem to be a major factor associated with abscission of ‘Calamondin’ and ‘Valencia’ fruit. The effect of inhibitors of protein and RNA synthesis on abscission of ‘Calamondin’ and ‘Valencia’ fruit was determined and cycloheximide was found to inhibit both abscission and increased cellulase activity. Cellulase-containing proteins extracted from tissues immediately surrounding and including abscission zones were separated electrophoretically and the appearance of a new protein band with carboxymethyl-cellulase activity was noted in this tissue during abscission.

Fruit Removal Force, Cellulase, and Ethylene Production in Release and Ethephon-treated Oranges1

“…In troduction of abscission agents to the abscission zone through the stem accelerates this phenomenon and lower concn are re quired than when an entire tree is sprayed in the field. Greater inherent cellulase activity has been measured in mature abscission zone tissue than immature (9). 'Hamlin' oranges used in this study were mature, with harvest operations underway.…”

“…Natural, wound, and chemically induced abscission are asso ciated with ethylene and hydrolytic enzyme production. Cellu lase enzyme activity was found to be a major factor in the dis solution of cell walls and subsequent reduction in citrus FRF (3,9,10,13). No polygalacturonase (PGase) activity was de tected (9,10).…”

“…Cellu lase enzyme activity was found to be a major factor in the dis solution of cell walls and subsequent reduction in citrus FRF (3,9,10,13). No polygalacturonase (PGase) activity was de tected (9,10). With refined techniques, concentration of the enzyme and the use of sodium hydrosulfite to inhibit oxidases (11) it appears PGase may also be active in citrus fruit abscission (4).…”

Relation of Ethylene and Cellulase Activity to Abscission of Freeze-Injured Citrus Fruit1

“…Some severely injured fruit that did not abscise were responsive to abscission-inducing chemicals. High internal ethylene content did not correlate as well with abscission as did high rates of abscission-zone cellulase activity.Evidence strongly indicates that ethylene plays a mediating role in leaf and fruit abscission (1,2,3,11,12). Cellulase synthesis is induced by ethylene, and its synthesis in the abscission zone precedes abscission (2,12).…”

“…Evidence strongly indicates that ethylene plays a mediating role in leaf and fruit abscission (1,2,3,11,12). Cellulase synthesis is induced by ethylene, and its synthesis in the abscission zone precedes abscission (2,12).…”