Extracellular Polysaccharides Produced by Suspension-Cultured Cells from Digitalis lanata*

Abstract

Extracellular polysaccharides (ECP) were isolated in yields of up to 4 mg/ml from the culture media of suspension-cultured cells from Digitalis lanata Ehrh. ECP content was increasing continuously over the first ten days of cultivation and then stayed constant until day 20. ECP were fractionated by ion-exchange chromatography into two neutral and one acidic fractions. Further fractionation was achieved by gel-permeation chromatography (GPC). One neutral fraction was separated into two distinct fractions with average molecular weights of 160 and 70 kDa, respectively. The second neutral fraction was hetero-disperse in GPC with average molecular masses of 112, 32, and 8 kDa. Polysaccharides of all neutral fractions consisted of glucose, xylose, galactose, and arabinose. Methylation analysis indicated these fractions to contain xyloglucans besides minor amounts of highly branched arabinogalactans. Xyloglucans were, using endo-β-(1→4)glucanase, fragmented into subunits which were identified mainly as tri- and pentasaccharides. The acidic fraction eluated as a single peak during gel-permeation chromatography with an average molecular weight of 56 kDa. Analysis of carbohydrate composition and linkage analysis indicated that this polysaccharide is an acidic arabinogalactan. 2,6-Dideoxysugars, the typical carbohydrate components of cardiac glycosides in Digitalis lanata, were not detected in ECP.

key words

Digitalis lanata Ehrh. - Scrophulariaceae - suspension culture - extracellular polysaccharides - xyloglucan - arabinogalactan