Spraying ethephon (2-chloroethylphosphonic acid) causes abscission of mulberry leaves, thus enables mechanical harvesting of the leaves. The experiments were conducted to correlate the ethephon-induced abscission to the cellulase activity of the abscission zone.
Ethephon of 3, 000ppm was sprayed to potted mulberry plants in the first and second experiments, and to the field-grown plants in the third experiment. Leaves were collected at definite time intervals after the treatment. The tissue of 4mm in length, including abscission zone was sampled, homogenized in phosphate buffer (pH 6.8) and centrifuged. The supernatant, as crude enzyme preparation, was put into Ostwald's viscometer togather with 0.4% (Exp. 1, 2) or 0.8% (Exp. 3) carboxymethylcellulose in phosphate buffer. The activity of cellulase was measured as change in flow time at 0 and 20 hours after the mixture was put in.
In the first experiment a crack was observed at the abscission zone at 48 hours after the treatment. Cellulase activity increased considerably at 36 and 48 hours after the treatment. In the second experiment using very young leaves, however, no sign of abscission nor any increase in cellulase activity was observed up to 72 hours after the ethephon treatment. In the third experiment cellulase activity began to increase one day after the treatment when no leaves abscised yet, then continued to be high level up to four days after the treatment when essentially all leaves abscised.
Excised leaves were enclosed in glass jar for one hour, and ethylene evolution was measured by gas chromatography. Ethylene evolution from the ethephon-treated leaves was highest at 3hours after the treatment (45mμl/g/hr), then decreased steadily until three days after the treatment when the level was about the same as that from control leaves.
Most results showed thus fairly good correlation between ethephon-induced abscission of mulberry leaves and cellulase activity at the abscission zone.