Tissue culture sycamore

Pectin-like material is secreted from suspension tissue culture cells of sycamore and the rate of secretion of these polysaccharides can be measured using radioactive arabinose which is incorporated into arabinogalactans. The addition of Ca increased the steady state rate of secretion within seconds. The stimulation was brought about by an action on the normal mechanism of cell-wall polysaccharide export from the cytoplasm. It seemed therefore that the fusion of the vesicles with the plasmamembrane was a rate-limiting step and is probably a control point. The action of the Ca " " was to increase the rate of fusion at the cell membrane so that there was an immediate increase in the amount of polysaccharide secreted (35). 

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). 

Arabans have been isolated from the cell walls of many dicotyledonous plants. Until recently, no homo-araban has been isolated specifically from primary cell walls. However, methylation analysis of the walls of suspension-cultured sycamore 123) and pea (55) cells strongly suggested that these primary cell walls possess arabans which are structurally similar to arabans obtained from other tissues or organelles. Recently, an araban, essentially free of other polysaccharides, has been isolated from a methylated sycamore cell wall polysaccharide fraction 5). 

Arabinogalactans have been isolated from the tissues of a variety of dicots. However, no arabinogalactan has been isolated from a source known to contain only primary cell walls. The glycosyl compositions of the arabinogalactans isolated from rapeseed cotyledons, rapeseed flour, larch wood, maple sap, the medium of suspension-cultured tobacco cells, the medium of suspension-cultured sycamore cells, and from soybean cotyledons are summarized in Table 2. 

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. 

It appears that the primary cell walls of suspension-cultured sycamore cells contain two hydroxyproline-rich proteins. One of these appears to be a structural protein found only in the wall, while the second is a glycoprotein which, in culture, is present in the wall in only small amounts and is predominently found in the culture medium. Of course, even the culture medium arabinogalactan hydroxyproline-rich protein is likely to be found in the cell wall in the intact tissues, as there is no culture medium for it to be dispersed in. 

We have analyzed the polar lipid composition of mitochondria (from both green and non-green tissues), peroxisomes, chloroplasts and non-green plastids. Some experiments have also been performed with isolated cells from sycamore, cultivated in liquid suspension. In this last case, a specific parameter for the culture, i.e. the oxygen content of the medium, has to be taken into account as far as the fatty acid content of the membrane glycerolipids is concerned . 

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