关键词：
Cell membranes
Plant cells
Yeasts
Glucans
Sitosterols
Vascular plants
Atoms
Molecules
Enzymes
摘要：
Every year, plants make more than 10~(11) metric tons of cellulose, the chainof glucose residues that is the principal component of the plant cell wall. However, biochemicaldissection of the three steps of cellulose synthesis--initiation of the sugar chain, elongation, andtermination--is still in its infancy. A notable advance has been the recent identification of theCesA genes that encode protein subunits of cellulose synthase, the rosette-shaped enzyme complex inthe plant cell plasma membrane that synthesizes cellulose (1-3). Despite this advance, it has stillproved difficult to coax plant extracts to make cellulose in the test tube--instead they makecallose, a wound-response polysaccharide. It is possible that cellulose synthase is particularlyfragile, or requires an intact membrane environment for activity. A big leap forward comes on page147 of this issue with the identification by Peng et al. (4) of the lipidsitosterol-β-glucoside (SG) as the primer for cellulose synthesis inplants.
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