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The role of ethylene and 2,4-D in the abscission process, and the induction of cellulase isoenzymes in the abscission zones of Citrus fruit at two physiological stages of fruit development, were studied using a new staining technique for the detection of cellulase isoenzymes in polyacrylamide gels following electrophoretic separation. Four to seven isoenzymes were detected in the shoot-peduncle (zone A) and peduncle-fruit (zone C) abscission zones; at least two of them could be detected at excision time, and of these at least one could not be connected with abscission. In the young fruit, ethylene enhanced and 2,4-D delayed both abscission and the formation of several isoenzyrnes. In the older fruit, ethylene enhanced and 2,4-D delayed the formation of isoenzymes at a time where no abscission occurred any more in zone A. A slower but significant increase in most of the isoenzyme activity detected was also observed in abscission zone A of untreated older fruit explants after excision. These results fully agree with those reported earlier in relation to total cellulase and polygalacturonase activity (Greenberg et al., Physiol. Plant. 34: 1, 1975) tested at the same stages of fruit development. It is suggested, that the generality of the concept that a rise in hydrolytic enzymes in the abscission zone is necessarily followed by separation of the organ should be re-evaluated. [ABSTRACT FROM AUTHOR]

High temperatures induced abscission of pepper (Capsicum annuum L. cv. Maor) reproductive organs at various developmental stages. The role of ethylene biosynthesis and auxin economy in high temperature induced abscission is described. High temperatures somewhat increased ethylene production in the reproductive organs, but the highest temperature treatment, which was the most active in inducing reproductive organ abscission, decreased it. In contrast to ethylene, l-aminocyclopropane-1-carboxylic acid levels increased significantly in response to high temperatures and correlated positively with the increase in temperature. High temperatures reduced indole-3-acetic acid levels and particularly auxin transport capacity in the reproductive organs. The data suggest that the reduction of auxin transport capacity is the major mechanism by which high temperatures induce reproductive organ abscission in pepper. [ABSTRACT FROM AUTHOR]

The abscission of citrus leaf explants demonstrates the well-known enhancing effect of ethylene and the delaying one of auxin when treatment is started at excision time. Total peroxidase activity increases differently in tissues of the blade, abscission zone, and petiole. The highest activity at zero time is recovered in abscission zone in which also the response to the abscission regulators is the most visible. Isoperoxidase profiles are modified in opposite directions by ethylene and auxin respectively. Both regulators affect the activity of the same cathodic and anodic isoperoxidases without any qualitative changes. By the same time, auxin-like compounds increase in isolated abscission zones at 24 h from excision and decrease at 48 h. The level of one inhibitor complex undergoes an inverse variation. It is suggested that the increase in auxin during the first stage of abscission is necessary for influencing the growth of cells which is required to cause abscission. [ABSTRACT FROM AUTHOR]