Gut histochemistry in Oikopleura dioica

The specific location of enzyme activities and storage material along the gut of Oikopleura dioica was investigated by means of histochemical, histoenzymatic an immunohistochemical techniques with optical and electron microscopes. Absorptive processes (alkaline phosphatase), active transport (ATPases) and nitrogen excretion (D-amino acid oxidase) occur along the entire gut in both ciliated microvillar and globular cells. The latter, typical of the left gastric lobe and the rectum, are also involved in endocytotic processes (exogenous peroxidase as a tracer) and intracellular digestion (alpha-amylase, aminopeptidase, acid phosphatase, 5'-nucleotidase, non-specific esterase). The giant cells of the gastric band participate in extracellular digestion. They contain secretory granules positive to various hydrolytic enzymes, the activity of which is recognisable in the lumen and in faecal pellets. Lipid storage occurs mainly in the right gastric lobe and the vertical intestine, and protein storage in the rectal granular cells.