Characterisation of extracellular polysaccharides from suspension culturesof apple (Malus domestica)

The polymers secreted by suspension-cultured apple cells were composed of 8 5% carbohydrate (76% neutral sugar and 9% uronic acid) and 15% w/w protein. The extracellular polysaccharides (ECPs) contain 23% XG and 59% AGPs. The monosaccharide composition of the ECPs consisted of Gal, Ara, Glc and Xyl, with smaller amounts of Rha, Fuc and Man. Fractionation of the ECPs by anio n-exchange chromatography yielded an unbound neutral fraction and a bound a cidic fraction. Monosaccharide and linkage compositions of each fraction we re determined. The neutral fraction (48% recovered carbohydrate) was compos ed of xyloglucan (XG; > 90 mol%) which was purified by selective precipitat ion with Fehling's solution to yield pure XG. The purified XG had a Glc:Xyl :Gal:Fuc ratio of 4.0:2.5:0.8:0.5; the XG was not O-acetylated. The structu re of the secreted XG was similar to that extracted from apple-pomace. The acidic fraction (52% recovered carbohydrate) was composed primarily of arab inogalactan-proteins (AGPs) as detected by the beta-glucosyl Yariv diffusio n test. The AGP had a Gal:Ara ratio of 1.3: 1.0. Minor amounts of arabinan, xylan and mannan were also detected in the ECPs. This study is the first e xamination of the polysaccharides secreted by apple cells grown in suspensi on culture. (C) 1999 Elsevier Science Ltd. All rights reserved.