Abstract
The tunic of Ciona intestinalis contains tunicin fibers, blood cells, and a mucopolysaccharide ground substance. [14C]Glucose is rapidly taken up by the epidermal cells of the body wall underlying the tunic. Radioactivity is incorporated into the tunic, eventually becoming uniformly distributed throughout this structure during the 21-day postlabeling period. This labeled material is easily removed by mild acid hydrolysis, a procedure that separates the ground substance and most protein from the tunic. We conclude that the majority of the [14C] glucose is utilized by the epidermal cells in the production of the mucopolysaccharide of the ground substance. Some label remains associated with the tunic residue even after extensive acid hydrolysis, however, indicating that only a small amount of the labeled glucose may be incorporated into the tunicin fibers themselves.