Synthesis of Extracellular Polysaccharide by Suspensions of Acer Pseudoplatanus Cells

Plant wall polysaccharides are intimately connected with maintenance of cellular form and control of cell growth (6). Many pathogenic fungi and bacteria attack plants with enzymes that degrade the wall polysaccharides. Yet little is known about the structure and synthesis of the noncellulosic polysaccharides, which constitute as much as 75 % of the cell wall (10). Study of wall polysaccharide has been hindered by the use of heterogeneous wall extracts. For example, pectin is solubilized with boiling water, protopectin with versene or dilute acid, and hemicellulose with alkali. These extraction procedures reduce the degree of polymerization of the polysaccharides and also alter the structure in various ways. It would be advantageous to isolate and characterize plant wall polysaccharides without the necessity of extraction. Sycamore cambial cells grown in suspension possess many desirable attributes for the study of polysaccharide structure and synthesis. Thornber and Northcote have published data on the composition of cambium cells in the intact sycamore (27) and Lamport has studied a wall-specific hydroxyprolinerich protein in sycamore cell suspensions (15). One of the chief assets of this system is its friability; the cells in suspensions can be handled almost like bacterial systems. The sycamore cells grow rapidly in large amounts and can be plated or transferred by pipette. Another advantage is that by continuous transfer one selects for rapidly growing cells so that the population in the logarithmic phase of growth is more uniform than cells of plant tissues. Furthermore the supply of metabolites is readily controlled, and every cell has direct access to the external medium containing these metabolites. When desirable the cells can be grown on a defined medium. Although various wall polysaccharides may turn out to be important in controlling cell growth, we have concentrated on the galacturonic acid containing polymers, since it is known that the carboxyl groups of galacturonic acid possess the ability to control cell growth (6). This paper reports the presence of external uronide containing polysaccharides in the culture fluid of sycamore cambial cells growing in suspension. The composition of these polysaccharides is described, as well as studies on the incorporation of glucose-C14 and various methyl donors into the methyl galacturonate residues. These polysaccharides are compared to normal wall polysaccharides.