Biosynthesis of extracellular polysaccharides by tuberose callus

Summary Extracellular polysaccharides (ECPs) were produced in liquid cultures of tuberose ( Poliantbes tuberosa L.) callus regardless of the cell growth cycle. The major component of the ECPs was called tuberose polysaccharide (TPS), which has a molecular weight (mol.wt.) of ≧ 10 6 . Using protoplasts labelled with 14 C-glucose, no 14 C-TPS was found, but two 14 C-labelled low molecular weight polysaccharides (L-1: 1 × 10 5 mol.wt., L-2: 2–3 × 10 4 mol.wt.) were secreted into the medium. Both L-1 and L-2 polysaccharides were also detected in the intracellular polysaccharide (ICP) fractions extracted from calluses, single cells and protoplasts. Based on the neutral sugar compositions of 14 C-labelled L-1, L-2 and TPS, the L-1 polysaccharide was identified as a putative TPS precursor. The addition of brefeldin-A blocked TPS production, whereas the intracellular synthesis of its precursor was not markedly inhibited. Histochemical and electron microscopic observations showed that TPS is deposited in the intercellular spaces among the surface cells of the callus mass.