Unusual morphological and cytochemical features of pit plugs in clathromorphum circumscriptum (Rhodophyta, corallinales)

Abstract

Ultrastructural and cytochemical study of pit plugs in Clathromorphum circumscriptum revealed two distinctive features. The large outer cap layer of the pit plugs was irregular in morphology and often deeply lobed. Some plug caps were poorly consolidated, consisting of disjunct pieces that were not in contact with the rest of the pit plug. As in other Corallinales, the outer cap layer was reactive to periodic acid Schifif, a carbohydrate stain, and mercuric bromophenol blue, a protein stain; it was also sensitive to digestion by two proteolytic enzymes. In addition, a lipid stain, Sudan black B, stained the outer caps. This was the first demonstration, in any species, of pit plug outer caps with a significant lipid component. Morphological and cytochemical features of pit plugs could be of value in elucidating relationships among some species of Clathromorphum. © 1991 The British Phycological Society.