Brefeldin A: a specific inhibitor of cell wall polysaccharide biosynthesisin oat coleoptile segments

The effect of brefeldin A (BFA) on the synthesis and incorporation of polys accharides, proteins and glycoproteins into the cell wall of subapical cole optile segments isolated from etiolated oat seedlings (Avena sativa L. cv. Angelica) has been investigated. In the presence of D-[U-C-14]-glucose, the incorporation of radioactive glycosyl residues into buffer-soluble, membra ne (matrix polysaccharides) and cell wall polysaccharides was drastically i nhibited by increasing concentrations of BFA up to 10 mu g.mL(-1). BFA also altered the pattern of these polysaccharides suggesting a different sensit ivity of glycosyltransferases toward the action of the drug. The incorporat ion of [U-(14)]-glycine or L-[U-C-14]-leucine into non-covalently- and cova lently-bound cell wall proteins as well as the incorporation of radioactive N-acetylglucosamine residues into the newly synthesised oligosaccharidic c hains of cytosolic, membrane and cell wall glycoproteins remained unchanged in the presence of 10 mu g.mL(-1) BFA. The data demonstrate that, in oat c oleoptile segments, BFA specifically inhibits the synthesis of cellulose an d matrix polysaccharides without altering the synthesis and incorporation o f proteins and glycoproteins into the cell wall. In addition, it is demonst rated that BFA does not affect the in vivo activity of glycosyltransferases involved in the transfer of N-acetylglucosamine from UDP-N-acetylglucosami ne to the oligosaccharidic chains of glycoproteins. (C) Elsevier, Paris.