TISSUE-RELATED CHANGES IN METHYL-ESTERIFICATION OF PECTIC POLYSACCHARIDES IN CAULIFLOWER (BRASSICA-OLERACEA L. VAR. BOTRYTIS) STEMS

Pectic substances are a major component of cell walls in vegetable pla nts and have an important influence on plant food texture. Cauliflower (Brassica oleracea L. var. botrytis) stem sections at different regio ns of the mature plant stem have been monitored for tissue-related cha nges in the native pectic polysaccharides. Chemical analysis detected appreciable differences in the degree of methyl-esterification (ME) of pectic polysaccharides. About 65% of galacturonic acid (GalpA) residu es were methyl-esterified in floret tissues. Relative ME showed a basi petal decrease, from 94% in the upper stem to 51% in the lower-stem va scular tissues. The decrease was not related to a basipetal increase i n glucuronic acid (GlcpA) residues. The monoclonal antibodies, JIM 5 a nd JIM 7, produced distinct labelling patterns for the relatively low- methyl-esterified and high-methyl-esterified pectin epitopes, respecti vely. Labelling was related to cell type and tissue location in the st em. Floret cell walls contained epitopes for both JIM 5 and JIM 7 thro ughout the wall. Stem vascular tissues labelled more strongly with JIM 5. Whereas pith parenchyma in the upper stem labelled more strongly w ith JIM 7, in the lower-stem pith parenchyma, JIM 5 labelling predomin ated. Localization of pectic polysaccharide epitopes in cell walls pro vides an insight into how structural modifications might relate to the textural and nutritional properties of cell walls.