Effect of Brefeldin A on cell-wall polysaccharide production in the red microalga Porphyridium sp. (Rhodophyta) through its effect on the Golgi apparatus

The cells of the red microalga Porphyridium sp. are encapsulated within a complex sulphated polysaccharide, comprising cell-wall-bound and soluble fractions. The current study investigated the involvement of the Golgi apparatus in the production of the sulphated polysaccharide by treating the cultures with brefeldin A (BFA), a membrane-traffic inhibitor of the Golgi apparatus. Addition of BFA (10-25 μM) upon inoculation (logarithmic-phase cells) decreased the contents of both bound and soluble polysaccharides. Exposure of stationary-phase cultures to BFA (20 μM) inhibited the formation of the cell-wall bound polysaccharide to a greater extent than that of the soluble polysaccharide. Under conditions of nitrate starvation, BFA treatment had a more marked effect on soluble than on bound polysaccharide formation, as was supported by ¹⁴C pulse-chase experiments. BFA addition up to the first 10 h of the cell cycle affected cell division and bound polysaccharide and starch contents. An ultrastructural study showed that exposure of the cells to 20 μM BFA for 16 h disrupted the integrity of the Golgi apparatus. The integrated results of this study demonstrate clearly that BFA affects the architecture of the Golgi apparatus and hence polysaccharide production in algal cells.