The Influence of Potential Inhibitors on the in vivo and in vitro Cell-Wall β-Glucan Biosynthesis in Tobacco Cells

Abstract

Summary Various compounds were investigated in view of their ability to influence the in vivo synthesis of cellulose in tobacco suspension cultured cells as well as the in vitro synthesis of ʲglucans with particulate enzyme preparations. Among the compounds tested in vivo , DCB was highly effective and specific for an inhibition of cellulose biosynthesis. Coumarin showed a similar specificity only at concentrations below 1 mM. On a concentration base DCB compared to coumarin was over 100 times more effective. All other potential inhibitors had detrimental effects upon the general cell metabolism. EDTA and EGTA were strong inhibitors of in vitro ʲ-glucan biosynthesis indicating that the enzymes involved in this process are dependent on divalent cations, especially on calcium ions. DCB and coumarin did not inhibit in vitro ʲ-glucan formation. Amphomycin and bacitracin, which are known as inhibitors of glycolipid synthesis, were inhibitory to in vitro aglucan synthesis. Beyond that, bacitracin showed detergent effects comparable to digitonin resulting in a stimulation of ʲ-glucan formation. Among the detergents tested, only digitonin was not detrimental to ʲ-glucan synthase activity. Digitonin at a concentration of 0.0125 % even caused an up to 4-fold stimulation of ʲ-glucan synthase activity, whereas concentrations higher than 0.25 % reduced the rate of in vitro ʲ-glucan synthesis. Furthermore, UDP was shown to be an inhibitor of ʲ-glucan synthase activity. The different modes of inhibition of amphomycin, bacitracin and UDP are discussed in view of a possible involvement of lipid-linked intermediates in cell-wall ʲ-glucan biosynthesis.