Cellulase activity increased in separation-zone tissues 1 day after "Valencia" orange (Citrus sinensis [L.] Osbeck) was treated with 20 micrograms per milliliter cycloheximide. Exocellulase was detected only in the separation zones of treated fruit, whereas endocellulase was present in zones from both treated and control fruit. Endocellulase activity in separationzone tissue of treated fruit was nearly three times as great as that in control tissues. Cellulase activity was restricted to separation-zone tissue. Pectinase and an albedo-macerating factor activity were very low and were not influenced by the treatment. The cycloheximide effect in these experiments was apparently caused by ethylene produced by wound tissue.Ethylene regulates enzyme synthesis by stimulating RNA and protein synthesis (1). Because of this general effect, several enzymes may be involved in cell loosening during abscission. The anatomical changes in the separation zones during abscission suggest that complex enzyme reactions take place (10, 12). Pectinase enzymes in bean (7, 13) and an albedo-macerating factor in citrus (11) apparently increase during separation-zone development. However, others (4, 8) have been able to relate only cellulase activity with the separation process. Ethylene increases the secretion of cellulase (exocellulase) from the cells as well as increases its synthesis (endocellulase) in the cells of some plants (3,4).Cellulase activity in the separation zones of citrus leaves and fruit is stimulated by ethylene (1, 2), and the abscission of citrus fruit is related to the level of ethylene in the fruit's internal atmosphere (5,6,9). Cycloheximide stimulates ethylene production in citrus fruit, which in turn promotes cellulase activity that causes loosening (6,9 Exocellulase was extracted from 2-mm sections of the separation zones. After vacuum infiltration of the sections with H20, they were placed in needle syringes in centrifuge tubes and centrifuged 10 min at 3000 rpm. The centrifugate was made up to 5 ml with pH 7.0 phosphate buffer. One ml of this enzyme extract was incubated 6 hr with 1.5% carboxymethyl cellulose at 40 C. Viscosity was determined in a microviscometer (9). The tissue from the separation zones was then homogenized in a blender with pH 7.0 phosphate buffer. Cellulase activity was determined by described methods (9).Five days after treatment of fruits with 20 ,ug/ml cycloheximide, endocellulase activity in 10 g fresh weight of flavedo, albedo, and fruit stems, 5 g of leaf petiole tissue, and 20 leaf separation zones was determined by methods similar to those for cellulase in fruit separation zones.RESULTS AND DISCUSSION Exoceliulase. Exocellulase was not detected in the separation zones from nontreated fruit, as measured by the viscosity changes of CMC (Fig. 1). The ethylene level in the internal atmosphere averaged 0.1 [kg/ml in these fruit. Less than 0.1 ,ug/ml causes very little loosening of fruit and apparently stimulates very little enzyme activity.In 6 hr the ethylene in treated fruit w...

No abstract

No abstract

No abstract