Mapping Woronin body position in Aspergillus nidulans.

The positions of all Woronin bodies in five germlings of Aspergillus nidulans prepared by plunge freezing and freeze substitution were determined by transmission electron microscopy. As expected, Woronin bodies were found near septa. High numbers of morphologically identical organelles were also found in apical regions. To verify that these organelles were authentic Woronin bodies, we used antibodies raised against the Neurospora crassa Woronin body matrix protein Hex1. Anti-Hex1 antibodies labeled Woronin bodies at septa and in apical regions of A. nidulans. In germlings that had not yet formed septa, at least fifty percent of Woronin bodies were found within 2.5 μm of the tip. In germ tubes that had formed septa, the total number of Woronin bodies remained the same, but only twenty percent were near the tip. Our results clearly establish that Woronin bodies are found in apical regions of Aspergillus germ tubes and suggest that Woronin bodies are transported from the apex to the more basal regions of the cell immediately before or during septation.