Localization of cytoplasmic water-soluble reserve (1→3)-β-glucans in Achlya with immunostaining

Abstract

The cytoplasmic water-soluble reserve (1→3)-β-glucans of Achlya are of two types: a small neutral and a large phosphorylated. These glucans have been localized using indirect immunolabelling with a commercial polyclonal antibody specific for(1→3)-β-D-glucopyranose linkages. The glucans were localized in large vesicles in the organelle-rich areas of the hypha, and in the large central vacuole in more mature areas. Preabsorption of the antibody with either purified neutral or phosphoglucan completely eliminated subsequent labelling of hyphal sections, indicating that this antibody can also be used to identify phosphorylated (1→3)-β-glucans. No labelling of the large population of apical vesicles was found suggesting that these reserve glucans are not directly involved in apical growth. Since the labelling occurred in association with vesicles and the central vacuole in the mature areas of the hypha and no other cytoplasmic sites showed conjugation, the vesicle and vacuole membranes probably contain the glucan synthase responsible for the biosynthesis of the reserve glucans. The hyphal walls, known to contain a large amount of insoluble (1→3)-β-glucans, were labelled as expected.

Key Words:

• immunogold electron microscopy
• storage polysaccharides
• vacuoles
• vesicles