Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 1, 1996
Publication Date: N/A
Interpretive Summary: Uncontrollable softening of fresh fruits and vegetables contribute significantly to the loss of quality and product. The cost of loss is estimated to be greater than $5 billion annually. Biochemical studies are providing knowledge on key enzymes involved in the ripening processes, so progress is being made in identifying possible genes that can be manipulated to control softening. Biochemical studies are not able to identify changes in specific sites of cell wall, thus ultrastructural analysis was undertaken to better understand the biochemistry of these sites. This research on the ultrastructural analysis provided information on possible biochemical composition of complex areas that connect cell walls of adjacent cells. This information will be useful to scientists in better interpretating biochemical findings of cell wall composition during fruit development and ripening. As more information becomes available on biochemical changes during ripening, key enzymes can be identified and genes manipulated in controlling softening and reducing quality losses.
In fleshy fruits, ripening is generally associated with a loss in tissue firmness resulting from depolymerization of wall components and separation of adjacent cells. In the regions of the wall that contain plasmodesmata, the usual sequences of ripening events, i.e. depolymerization of the middle lamellae and splitting of the walls, are not observed. The present study attempts to characterize the structural microdomain of the cell wall that surrounds the plasmodesmata by in muro visualization of the cell wall components. Anionic sites of galacturonic acid were labeled with cationic gold. Unesterified homogalacturonic sequences were labeled with the monoclonal antibody JIM5 and esterified homogalacturonic sequences with JIM7. In addition, a polyclonal antibody directed towards B(1,3) glucopyranose was used to target callose in situ. The results indicated that the plasmodesmata-wall composed of unesterified homogalacturonic sequences that were not involved in calcium cross-bridging but were probably surrounded by a cationic environment. These structural features may result in the prevention of normal cell wall separation in regions containing plasmodesmata. However, low temperature scanning electron microscopy observations suggested that mechanical separation of these walls ruptured the plasmodesmata and ultimately resulted in the spatial separation of adjacent cells.