Abscission in leaf and fruit explants of Prunus persica (L.) Batsch

Abstract

SUMMARYStructural and enzymatic aspects of leaf and fruit abscission in explants treated with exogenous ethylene were studied and compared with those previously observed under field conditions. Light and electron microscopy observations reconfirm that differences in abscission occur in leaf and fruit, and in explants cell separation is accelerated, with a more dramatic degradation of the cell walls. In fruit, digestion starts from the middle lamella, and subsequently extends to the entire parietal mass. In the leaf the process involves the primary cell wall, leaving, at the end, undigested materials. In fruit the lytic activity is sustained by endocellulase, and by exo-as well as endopolygalacturonase. In the leaf only endocellulase activity has been found. Cell enlargement phenomena occur subsequent to abscission zone activation in both leaf and fruit explants, involving the cells of either the separation layer or the adjacent region.

Characterization of abscission zones in the flowers and fruits of peach [Prunus persica (L.) Batsch]

“…Previous studies showed that in fruits at a late growtb stage, this abscission zone can be morpbologically distinguished from the surrounding tissues due to its small sized cells and the very few intercellular spaces (Rascio et al, 1985;Zanchin et al, 1993). Therefore, as generally considered for the morphologically predifferentiated abscission zones (Sexton & Roberts, 1982;, it is plausible to regard this morphological predifferentiation as a prerequisite necessary to the AZ3 cells for the acquisition of sensitivity to the abscission stimuli.…”

“…The two cell separation modes, whicb coincide with tbose already observed in leaf AZ and fruit AZ3 (Zanchin et al, 1993), might actually be the modes of response to abscission stimuli of the plant vegetative and reproductive bodies, respectively.…”

“…For each experiment, evaluation was made on abscission zones of 200 explants. Samples containing the various abscission zones were collected before and throughout the ethylene treatment and processed for light and electron microscopy according to Zanchin et al (1993).…”

“…Enzyme extraction and assays of activity by viscosimetric (endopolygalacturonase and endocellulase) and spectrophotometric methods (exopolygalacturonase and exocellulase), respectively, were carried out as described in Zanchin et al (1993).…”

“…Nevertheless, physiological dif-a/., 1993; Webb e< a/., 1993), but differences can also ferences are always present since cells of abscission be found in different organs of the same plant. Thus, zones are the only ones capable of responding to the in peach previous research has shown (Rascio et al, inductive stimuli which, through a series of events, 1985;1987;Zanchin et al, 1993) that abscission at lead to the loss of adhesion between adjacent cells the fruit-peduncle junction (AZ3) is brought about and consequent shedding of the given organ, by cellulase and polygalacturonase activities with Ethylene is the main hormone involved in both consequent degradation of both middle lamella and activation and control of rate of abscission (Sexton et primary cell wall. In contrast, only cellulase activity al., 1985;MacManus & Osborne, 1989;Burdon & and primary cell wall degradation are involved in .…”