Compositional and structural modification of the cell wall of cauliflower (Brassica oleracea L var botrytis) during tissue development and plant maturation

The purpose of this study was to investigate maturation-related changes in cell-wall polysaccharides in cauliflower (Brassica oleracea L.) florets and stem tissues. Alcohol insoluble residues (AIRs) prepared from these were a nalysed for their carbohydrate composition. The cell walls of the immature tissues contained arabinose- and galactose-rich pectic polysaccharides and the major hemicelluloses consisted of xyloglucans. Maturation was accompani ed by a basipetal decrease in the galactose- and arabinose-containing pecti c polymers and a decrease in their degree of methyl-esterification. At the same time, there was a considerable increase in (1 --> 4)-linked xylose res idues and cellulosic glucose, particularly in the lower stem, and an increa se in Klason lignin. More precise information on polymer structure was obta ined from sequential extraction (with water, cyclohexane-trans-1,2-diamine- N,N,N',N'-tetra acetate, Na2CO3 and KOH) of the AIRs of upper and lower ste m tissues. The cellulose-rich residues remaining contained significant amou nts of pectic polysaccharides, a proportion of which was released on neutra lization of the residues. The greatest differences between the immature and mature stem cell-wall polymers occurred in the 0.5 M KOH fractions and the se were investigated in more detail. Glycosidic linkage analysis showed tha t the insoluble residues from the immature stem contained much larger amoun ts of arabinose-rich pectic polysaccharides, and lower amounts of acidic xy lans, compared with the mature stem. GC-MS linkage analysis of the polysacc haride fractions recovered from graded EtOH precipitation of the soluble fr actions showed a large proportion of the maturation-related increase in (1 --> 4)-linked xylose comprised glucuronoxylans closely associated or comple xed, with pectic polysaccharides and xyloglucans. The possible relationship between such complexes and the onset of lignification is discussed. (C) 19 99 Elsevier Science Ltd. All rights reserved.