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ULTRASTRUCTURAL STUDIES OF ABSCISSION IN PHASEOLUS: LOCALIZATION OF PEROXIDASE'

A B S T R A C T Segments of leaf abscission zone tissue of Phaseolus vulgaris L. cv. Red Kidney were fixed in glutaraldehyde, incubated to demonstrate peroxidase activity in medium containing 3,3'diaminobenzidine (DAB) and postfixed in osmium tetroxide. Electron microscopic observation of treated tissue revealed pronounced deposition of highly electron-opaque material in the form of granules or globules in cell walls, on mitochondrial membranes, associated with rough endoplasmic reticulum and along the plasmalemma and tonoplast. This distribution pattern was typical of both non-treated and ethephon-treated tissue. Ethephon-treated material also contained these granules within cytoplasmic vacuoles. It is suggested that pH of the incubation medium may affect localization sites and that exposure of tissue to light during incubation may modify localization patterns. Differing patterns of distribution of the reaction product in treated and non-treated tissue may reflect changes in membrane permeability and microfibrillar modifications related to ethephon treatment.