Brefeldin A induces the accumulation of unusual membrane structures in elongating pollen tubes of Nicotiana tabacum L.

To investigate the effects of a specific inhibitor of the post-Golgi secretion on the secretory pathway in the plant cell, the growing pollen tubes were treated with Brefeldin A (BFA) and examined at the ultrastructural level. BFA-treated pollens were processed by rapid-freezing and freeze-substitution for the preparation of samples for electron microscopy. BFA completely inhibited the elongation of pollen tubes and the secretion of vesicles in the tip region, and dictyosomes disappeared in BFA-treated pollen tubes. Unusual membrane structures, filled with various types of electron-dense matrix, were observed in both the pollen tubes and grains after exposure to BFA. Some of the structures contained cell-wall-like fibrous structures, and the results of cytochemical analysis indicated that the membranes were similar to plasma membranes of control pollen tubes. These membranes were ribosome-free, and clathrin-like coats were observed on the surface of the membranes on the cytosolic side. From these observations, it seems that processing of glycoproteins and membranes can proceed in BFA-treated pollen tubes.