Further comparative studies of pectin esterase in relation to leaf and flower abscission

The possible role of pectin esterase in abscission of bean and coleus leaves was re-examined using improved methods for its extraction. Its possible role in abscission of flowers of tobacco and leaves of soybean. cotton, mulberry, magnolia, and euonymus was also examined. In seven of the eight species, no detectable changes in abscission zone pectin esterase activities immediately preceded abscission. Therefore, pectin esterase probably plays no causal role in abscission in these species.In coleus, activity in the abscission zone's distal portion decreased by one-half at most and remained unchanged in its proximal portion with abscission's onset. Also accompanying abscission in coleus was a decrease in the proportion of abscission zone pectin esterase extractable with 3 m sodium chloride at pH 7. These changes were not a general concomitant of senescence as they were not detected in the middle of abscising coleus petioles. Pectin esterase may play a role in coleus leaf abscission.