Effect of Brefeldin A on the synthesis and transport of cell wall polysaccharides and proteins in pea root seedlings

The in vivo effect of Brefeldin A (BFA) on the synthesis and transport of cell wall polysaccharides and proteins in the roots of pea seedlings (Pisum sativum L. cv. Alaska) was investigated. BFA (10 //gml") inhibited the synthesis of cell wall matrix polysaccharides by approximately 43%. Under the same conditions, cellulose synthesis was inhibited by approximately 77%. The percentage of incorporation of L-[U-C]leucine and L-[U-C]proline into cytosolic, membrane and cell wall proteins was only slightly changed in the presence of BFA. In addition, the drug did not change the pattern of newly synthesized proteins in the three fractions as judged by SDS-PAGE fluorography. Double labelling of proteins and cell wall polysaccharides confirmed the above reported data. All these results showed that the synthesis and transport of proteins to the cell wall was only slightly affected by BFA under similar conditions to those which brought about a strong inhibition of the synthesis of matrix and cellulosic polysaccharides. BFA had no effect on the activity of membranebound and digitonin-solubilized mannan and glucomannan synthase isolated from the third internode of pea seedlings. This would exclude an effect of BFA at the level of the catalytic site of the synthases. The inhibition of polysaccharide synthesis by the drug was rapidly eliminated after its removal. It is concluded that the effect of BFA on the biosynthesis of cell wall polysaccharides could be caused by an interaction of the drug with the topological organization of the synthase complexes in the membranes. This effect would precede the action of the drug at the level of vesicle transport to the walls.