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

The effect of brefeldin A (BFA) on the synthesis and incorporation of polysaccharides, proteins and glycoproteins into the cell wall of subapical coleoptile 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, membrane (matrix polysaccharides) and cell wall polysaccharides was drastically inhibited by increasing concentrations of BFA up to 10 mu g.mL(-1). BFA also altered the pattern of these polysaccharides suggesting a different sensitivity of glycosyltransferases toward the action of the drug. The incorporation of [U-(14)]-glycine or L-[U-C-14]-leucine into non-covalently- and covalently-bound cell wall proteins as well as the incorporation of radioactive N-acetylglucosamine residues into the newly synthesised oligosaccharidic chains 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 coleoptile segments, BFA specifically inhibits the synthesis of cellulose and matrix polysaccharides without altering the synthesis and incorporation of proteins and glycoproteins into the cell wall. In addition, it is demonstrated that BFA does not affect the in vivo activity of glycosyltransferases involved in the transfer of N-acetylglucosamine from UDP-N-acetylglucosamine to the oligosaccharidic chains of glycoproteins.