OBSERVATION OF THE CONTINUITY OF GOLGI-APPARATUS WITH ENDOPLASMIC-RETICULUM INDUCED BY BREFELDIN-A STUDIED BY ZINC IODIDE OSMIUM STAINING IN TOBACCO PROTOPLASTS

We aimed at investigating the continuity of the Golgi apparatus into t he endoplasmic reticulum (ER) in cultured tobacco protoplasts by zinc iodide-osmium (ZIO) staining. The density of the membranes of both Gol gi cisternae and the ER was, at first analysed by measuring their peak contrast on software:NIH Image 1.60. Membranes of the Golgi cisternae were differentially densely stained when the protoplasts were immerse d in the ZIO mixture for 16 h. These Golgi membranes were more clearly identified than those stained with uranyl acetate alone. After treatm ent with 10 mu g ml(-1) brefeldin A (BFA) for 3 h, the distorted Golgi cisternae became wider and longer than those in control protoplasts. The expanded cisternae were loosely organized and their tips appeared to extend into the ER. In ZIO stained sections, the density (the mean value of peak contrast) of the membranes of the Golgi cisternae elonga ted to the ER were the same as those of the ER after treatment of the drug for 3 h. These results indicate that the extended cisternae of th e Golgi apparatus continued into the ER after 3 h treatment of BFA.