Synthesis of Arabinose-Containing Cell Wall Precursors in Suspension-Cultured Tobacco Cells I. Intracellular Site of Synthesis and Transport

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The distribution of arabinose-containing macromolecules in suspension-cultured tobacco cells was examined using sucrose density gradients. Exogenously applied ^<14>C-arabinose was scarcely converted into other sugars, and concentrated in the Golgi-rich fraction (1.15 g/cm^3) and then secreted to the cell wall. ^<14>C-Arabinose was also incorporated in a lower sucrose density fraction (1.11 g/cm^3), which contains small vesicles presumably originated from the Golgi apparatus. The arabinose-containing macro-molecules in this fraction was more easily solubilized in water than those in the Golgi-rich fraction. Alkaline hydrolysis of the macromolecules indicated that cell-wall glycoprotein is a major component of the macromolecules and that the degree of glycosylation is slightly greater in the lower density fractions than in the Golgi-rich fraction. Based on these results, a scheme is suggested in which the glycoproteins and polysaccharides are glycosylated in the Golgi apparatus and secreted to the cell wall via secretion vesicles in t,he low density fraction. The possibility of ^<14>C-arabinose-containing macromolecules, in the early phase of synthesis, being a marker of the plant Golgi apparatus is also proposed.
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