A Comparative Ultrastructural Study of Cyanidium caldarium and the Unicellular Red Alga Rhodosorus marinus

Abstract

The presence of nucleus, chloroplasts, mitochondria, microbodies and a vacuole are confirmed in Cyanidium caldarium strain CCAP 1355/1. Chloroplasts usually contain parallel rows of unstacked thylakoids surrounded by a peripheral thylakoid, although the concentric arrangement has also been observed. The chloroplast envelope consists of two closely appressed membranes which can only be resolved after gluteraldehyde—osmium fixation. The chloroplast of Rhodosorus marinus also contains parallel, unstacked thylakoids surrounded by a peripheral thylakoid but, in addition, a prominent, stalked pyrenoid projects into the cytoplasm and is bounded by both the peripheral thylakoid and the chloroplast envelope. This structure is covered by a cap of starch grains and contains membranous vesicles in the matrix. Phycobilisomes are absent from the chloroplasts of both algae. The recognition of C. caldarium as a rhodophyte is supported by these observations.