BREFELDIN-A INDUCES REVERSIBLE DISSOCIATION OF THE GOLGI-APPARATUS INTHE GREEN-ALGA MICRASTERIAS

The fungal metabolite brefeldin A (BFA) causes inhibition of cell grow th in Micrasterias denticulata after 2 h incubation, combined with sli ght malformation of the cell shape. The BFA effects on cell developmen t are accompanied by a gradual decrease in the number of Golgi cistern ae and severe structural and morphological changes of the dictyosomes which are already visible after only 10 min exposure. When the treatme nt is prolonged the number of dictyosomes is markedly reduced, leading to almost complete loss of Golgi bodies, particularly in the young se micell. Groups of primary wall material-containing vesicles accumulate d in areas of former dictyosomes, and previously unknown vesicular bod ies are found. Restitution of almost normal dictyosomes occurs within 5 h when the cells are allowed to recover from BFA treatment. Micraste rias cells incubated in BFA at concentrations below 15 mu M maintain t heir ability to divide over several generations. Our results indicate that, of the various inhibitors of the secretory pathway tested agains t growing Micrasterias cells, BFA is the only drug which induces compl ete and reversible dissociation of dictyosomes in the growing semicell . This allows deductions about the function of the processes targeted by BFA during cell development in Micrasterias.