PLANT PHYSIOLOGY , Vol 114, Issue 2 539-547, Copyright © 1997 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Characterization of the Cell Wall Microdomain Surrounding Plasmodesmata in Apple Fruit
S. Roy, A. E. Watada and W. P. Wergin
Horticultural Crops Quality Laboratory, United States Department of Agriculture, Agricultural Research Service, Beltsville, Maryland 20705 (S.R., A.E.W.)
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. In the present study
we attempted to characterize in apple (Malus domestica Borkh.) fruit the
structural microdomain of the cell wall that surrounds the plasmodesmata by
in muro visualization of the cell wall components. Anionic sites of
galacturonic acids were labeled with cationic gold. Low-esterified
homogalacturonans were labeled with the monoclonal antibody JIM 5. In
addition, a polyclonal antibody directed toward
[beta](1->3)-glucopyranose was used to target callose in situ. The
results indicated that the plasmodesmata-wall complexes were surrounded by
a pectic microdomain. This domain was composed of low-esterified
homogalacturonans 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, observations by low-temperature scanning
electron microscopy suggested that splitting of these walls ruptured the
plasmodesmata and ultimately resulted in the spatial separation of adjacent
cells.
