IMMUNOCYTOCHEMICAL STUDIES OF AXIAL RESIN CANALS. I. LOCALIZATION OF NON-CELLULOSIC POLYSACCHARIDES IN EPITHELIUM OF NORWAY SPRUCE XYLEM

The microdistribution of non-cellulosic polysaccharides in epithelial cells of axial resin canals was investigated in Norway spruce xylem using immunolocalization methods combined with monoclonal antibodies specific for (1 -> 4)-beta-galactan (LM5), (1. 5)-alpha-arabinan (LM6), homogalacturonan (LM 19, LM20), xyloglucan (LM15), xylan (LM10, LM11) and mannan (LM21, LM22). The ultrastructure and lignin distribution of epithelial cell walls was also examined after cytochemical staining for lignin. Compared with tracheids, epithelial cells showed several different ultrastructural characteristics, such as the thickness of three layers forming the cell wall, the boundary structure between layers and the lamellate structure of cell walls, with slightly stronger reaction with chemical staining for lignin than tracheids. After staining with potassium permanganate, the layer of the epithelial cell wall adjacent to the canal showed typical characteristics of middle lamella (C-ML). However, C-ML regions showed completely different chemical characteristics from E-ML (middle lamella between epithelial cells) regions of epithelial cells and compound middle lamella (CML) regions of tracheids. Unlike tracheids, epitopes of pectic polysaccharides were detected in the epithelial cell wall with variations in amounts between cell wall layers. Epitopes of hemicelluloses were also detected in the epithelial cells with differences in distribution patterns from tracheids, particularly xyloglucan (LM15) and low substituted xylan (LM10) epitopes. Together, our results suggest that the ultrastructure and chemistry of epithelial cells including C-ML regions significantly differ from tracheids.