ANALYSIS OF THE DISTRIBUTION OF GLYCOCONJUGATES IN THE DIGESTIVE GLAND OF THE BIVALVE MOLLUSK MYTILUS-GALLOPROVINCIALIS BY CONVENTIONAL ANDLECTIN HISTOCHEMISTRY

We examined the distribution and pattern of reactivity of a panel of 1 6 lectins in the digestive gland of the bivalve mollusc Mytilus gallop rovincialis at the light-microscopic level. Various chemical treatment s were applied in combination with lectins to differentiate between N- and O-linked oligosaccharides. Several control reactions were carried out, including replacement of lectins by buffer and incubation with t heir specific competitive inhibitors. Some lectins reacted selectively with particular cell types, thus revealing a cell-specific glyco-conj ugate distribution pattern which is possibly related to the metabolic role of each cell type in the digestive gland. Glycoconjugates contain ing glucosamine, man nose, and sulfated galactose were associated with the endolysosomal system of digestive cells. These glycoconjugates we re also found in small vesicles randomly distributed in the cytoplasm of adipogranular cells in the connective tissue. However galactosamine residues appeared to be associated mainly with basophilic cells. Fuco se residues did not exhibit a cell-specific distribution and appeared in small amounts homogeneously distributed throughout the digestive gl and tissue. Conventional histochemical reactions for carbohydrate dete ction revealed moderate amounts of periodic-acid-Schiff-positive, neut ral carbohydrates widely distributed in digestive and connective tissu es. Among the acid carbohydrates, most cell types contained complex su lfated carbohydrates, but not carboxylated ones; this agreed well with the complete lack of sialic acid residues in all cell types studied, as observed by lectin histochemistry.