Localization of cell wall polysaccharides during kiwifruit (Actinidia deliciosa) ripening

The localization of pectin, cellulose, xyloglucan, and callose was compared in kiwifruit (Actinidia deliciosa [A. Chev.] C. F. Liang and A. R. Ferguso n var. deliciosa "Hayward") at harvest, at the end of the first phase of so ftening, and when ripe. Pectin was visualized using three different methods : labeling of galacturonic acid residues, labeling of negatively charged gr oups, and labeling with JIM 5 (nonesterified residues) and JIM 7 (methyl-es terified) monoclonal antibodies. Labeling of pectin gave different results depending on the detection system used. Differences related to patterns of change during ripening and to spatial distribution of label intensity. Cell wall pectin was available for labeling at all stages of fruit softening, b ut no clear differentiation of the middle lamella region was seen, although JIM 5 binding predominated where the middle lamellae joined the intercellu lar spaces in unripe fruit. Negatively charged groups (cationic gold labeli ng) and, to a lesser extent, galacturonic acid residues (Aplysia depilans g onad lectin labeling) were preferentially located near the cell wall/plasma membrane boundary. The lack of strong binding of the JIM antibodies indica ted that the reactive groups were inaccessible. Cellulose remained intact a nd labeled densely across the wall at all stages of fruit ripening. Distrib ution of xyloglucan was patchy at harvest but was scattered throughout the wall later in ripening. Alterations to labeling of xyloglucan indicated tha t some epitopes were differentially exposed. Plasmodesmatal regions were cl early different in composition to other wall areas, showing an absence of c ellulose labeling, specific pectin labeling, and callose presence. A simila r predominance of pectin labeling compared with cellulose also occurred at the middle lamella wedge near intercellular spaces.