Chemical and structural features of kiwifruit cell walls: Comparison of fruit and suspension-cultured cells

Chemical and structural features were compared in cell-wall polysaccharides isolated from intact kiwifruit (Actinidia deliciosa) and suspension-cultured cells initiated from the same fruit. Morphological features of the cells and whole fruit tissue were also examined by electron microscopy. Cell-wall material (CWM) from cultured cells contained less cellulose, more protein, and had a higher degree of acetylation than cell-wall material from intact fruit. Whereas galactose was the major neutral sugar in the pectic polysaccharides of intact fruit, arabinose was predominant in cultured cells. The arabinose occurred as terminal and 5-substituted residues, presumably as neutral side-chains attached to the galacturonan backbone which was more highly branched in the cultured cells. The most significant structural difference in the hemicelluloses occurred in a galactoglucomannan purified from the 4 M KOH-soluble fraction. The backbone of the galactoglucomannan of the cultured cells was more branched than that in the intact fruit, with 84% of the 4-linked mannosyl residues substituted at O-6 with either single galactosyl or galactosyl-(1 → 2)-galactosyl groups. In intact fruit ∼ 30% of the mannosyl residues were substituted at O-6. Rhamnogalacturonan II (RG-II) was partially purified from CWM and shown to possess a very similar composition of glycosyl residues in both intact fruit and cells. However, the primary cell walls of the cultured cells contained twice the amount of RG-II found in the cell walls of intact fruit.