Scanning Electron Microscopy, Video-image Analysis, and Confocal Imaging of Changes Occuring during Peach Fruit Abscission

Abstract

`Redhaven' peach (Prunus persica L. Batsch) fruit abscission has been investigated using scanning electron microscopy, computer-assisted video-image analysis, and confocal laser scanning microscopy in conjunction with chlorotetracycline and ethidium bromide as fluorescent probes for membrane Ca2+ and nuclear DNA. This enabled us to document the morphological changes of the cells, distribution patterns of membrane Ca2+ in the constituent cells of the abscission zone, and the nuclear morphology with accompanying changes in nuclear DNA. The digitized images of CTC-fluorescence emissions revealed that the membrane Ca2+ levels in the pre-abscission zone (control) is uniform and similar to that present in the cells of the spongy proximal region of the peduncle and that of the fruit parenchyma. However, with the induction of abscission, 2 days after embryoctomy, there was a significant increase in membrane Ca2+ in the cells of the abscission zone compared to the neighboring cells of the fruit and the peduncle. Thereafter, with the gradual separation of the cells and the concomitant vacuolation, the membrane Ca2+ level decreased substantially. Confocal imaging of EB labeled cells of the abscission zone before induction invariably revealed a well-organized nucleus. However, during cell separation, significant changes in the cellular and nuclear morphology occured, including 1) rounding of cells, 2) reduction in the nuclear volume, and 3) concomitant fragmentation of nuclear DNA. The possible role of Ca2+ during the process of peach fruit abscission and nuclear DNA fragmentation leading to cell death is discussed. Chemical names used: chlorotetracycline (CTC), ethidium bromide (EB).