Sycamore cell wall studies

Clearly, branched arabinans are important, primary cell-wall components, but considerable further study is needed before it will be possible to draw even a tentative structure for the intact-wall component. Isolation and analysis of the arabinan of sycamore cell-wall is of current interest, a study augmented by the availability of two purified enzymes, endo-a-(l— 5)-arabinanase63 133 and exo-a-arabinosidase.63... 

It is difficult to draw even a tentative structure of the primary cell wall araban. Clearly, branched arabans are important primary cell wall components. Efforts are currently under way in this laboratory to isolate and structurally analyze the araban of sycamore cell walls. This study is augmented by the availability of two recently purified enzymes, endo-a-l,5-arabanase and an exo-arabinosidase 69, 130). 

Studies on citrus pectin and sycamore cell wall. Unpublishedresults. 

Those galactans that have been studied (see the preceding) have degrees of polymerization ranging from 33 in white willow161 to 50 in sycamore-cell primary-walls.183 These values were obtained by vapor pressure and osmosis studies,161 and by comparing the ratio of terminal to intrachain galactose units by methylation analysis.163... 

Recently, the physiological roles of extracellular components have been studied. Biologically active cell-wall fragments in sycamore maple (Acer pseudopla-tanus) cells have been related to amino acid transport and protein synthesis (50, 147) and to the control of morphogenesis (134 Sect. 5.1.3.3). 

Suspension-cultured plant cells represent a somewhat artificial situation since one is interested in studying the cells of the intact plant. The structures of the walls of cells in culture and the walls of cells in the plant may conceivably differ and it is essential when studying suspension-cultured cells to keep this possibility in mind. However, the available data indicate that the walls of suspension-cultured cells are very similar in structure to the walls of intact plant tissues. Cell wall glycosyl and glycosyl-linkage compositions of pea (58) and red kidney bean (105) hypocotyl tissues show that these tissues contain walls which are very similar to the walls isolated from suspension-cultured sycamore (123) and suspension-cultured red kidney bean cells (105). In addition, it has been demonstrated that the primary walls of cambial cells which were prepared from the branches of sycamore trees are very similar to the walls of suspension-cultured sycamore cells (104). 

Many of the structural studies discussed in this review have relied upon the use of a few well-defined experimental techniques. These techniques will be described in this section. Particular emphasis is placed on those methods which have proved useful in studying the structures of primary cell wall polysaccharides and, in particular, the wall polysaccharide of suspension-cultured sycamore cells. 

Considerably later, xyloglucans were isolated from the medium of suspension-cultured sycamore (24) cells, and, finally, from the primary cell walls of suspension-cultured sycamore cells (31). The basic structure of xyloglucans was elucidated by Kooiman (79) who studied the amyloid of Tamarindus indica seeds. The xyloglucans of primary cell walls were isolated and structurally characterized before it was recognized that the xyloglucans are very similar to the amyloids 31). The widespread occurrence of the amyloids 21, 67, 79, 115, 119) and xyloglucans 24, 29, 31) shows that polysaccharides isolated from tissues other than primary cell walls can, at times, serve as excellent models for the cell wall polysaccharides. 

Methylation analysis of the tetra-arabinosides isolated from primary cell walls of tomato and sycamore indicates that the arabinosyl residues are terminal and 2- and 3-linked (71, 123). Akiyama and Kato (2) have studied the hydroxyproline arabinosides obtained from suspension-cultured cells of tobacco (Nicotiana tabacum). These workers used periodate oxidation (Smith degradation), methylation analyses, NMR, and optical rotation to show that the structure of the hydroxyproline tetra-arabinoside is Araf-(1 3)-Araf-(l - 2)-Arar(l - 2)-Arar(l - 4)-hydroxyproline. 

Studies on the Pectic Polysaccharides of the Primary Cell Walls of Sycamore... 

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