Hyphal tip growth in Achlya. I. Cytoplasmic organization.

Growing apices of Achlya ambisexualis Raper hyphae were examined by electron microscopy using cytochemical techniques. Apical vesicles can be grouped into two major classes based upon size and cytochemical reactions. Vesicles of the most prominent class are about 150 nm in diameter and possess contents which appear fibrous in thin section. This fibrous material reacts positively with the periodic acid-silver methenamine (PASM) cytochemical test for polysaccharides. Most of these same vesicles also display IDPase activity, and a smaller number display acid phosphatase activity. Vesicles of the second class are about 80 nm in diameter, and include coated vesicles and others which react positively for IDPase activity. They show a negative PASM reaction in contrast with the larger vesicles. Some of these smaller vesicles are stained by the phosphotungstic acid-chromic acid (PTA-CrO3) stain, whereas 150-nm vesicles are not. The source of at least some vesicles of both major classes appears to be the Golgi apparatus. It is proposed that the IDPase activity and carbohydrate content of the 150-nm cytoplasmic vesicles could serve as useful markers in their isolation.