Changes in the sugar composition and molecular mass distribution of matrix polysaccharides during cotton fiber development

Cotton (Gossypimn herbaceum L.) fiber development consists of a fiber elongation stage (up to 20 d post-anthesis) and a subsequent cell wall thickening stage. Cell wall analysis revealed that the extractable matrix (pectic and hemicellulosic) polysaccharides accounted for 30-50% of total sugar content in the fiber elongation stage but less than 3% in the cell wall thickening stage. By contrast, cellulose increased dramatically after the fiber elongation ceased. The amounts of extractable xyloglucans and arabinose- and galactose-containing polymers per seed increased in the early fiber elongation stage and decreased thereafter. The amounts of extractable acidic polymers and non-cellulosic beta-glucans (mainly composed of beta-1,3-glucans) increased in parallel with fiber elongation and then decreased. The molecular masses of extractable non-cellulosic beta-glucans, and arabinose- and galactose-containing polymers decreased during both fiber elongation and cell wall thickening stages. The molecular mass of extractable xyloglucans also decreased during the fiber elongation stage, but this decrease ceased during the cell wall thickening stage. Conversely, the molecular size of acidic polymers in the extractable pectic fraction increased during both stages. Thus, not only the amounts but also the molecular size of the extractable matrix polysaccharides showed substantial changes during cotton fiber development.