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.