ULTRASTRUCTURE AND PIGMENTS OF TWO STRAINS OF THE PICOPLANKTONIC ALGAPELAGOCOCCUS SUBVIRIDIS(CHRYSOPHYCEAE)1

Abstract

ABSTRACTThe organelle ultrastructure and photosynthetic pigments of a new isolate of the picoplanktonic alga Pelagococcus subviridis Norris from the East Australian Current was compared with the North Pacific Ocean type species. No differences in the ultrastructure of the two isolates were observed. Mitosis was studied in detail in the Australian strain, and showed two unusual features: the de novo appearance of centrioles prior to mitosis, and the formation of a small, extra‐nuclear spindle.The major carotenoids in both strains were fucoxanthin and a 19′‐butanoyloxyfucoxanthin‐like pigment, with diadinoxanthin and diatoxanthin as secondary pigments. Several minor carotenoids have not yet been identified. In addition to chlorophylls a and c2, a new chlorophyll c derivative (chlorophyll c3), present in both strains, was separated by high‐performance thin‐layer chromatography (HPTLC). The Australian isolate, unlike the type material, showed no evidence of chlorophyllase activity during cell harvest and extraction.While the pigment composition suggests affinities with certain newly examined prymnesiophytes, organelle ultrastructure indicates Pelagococcus to be a member of the Chrysophyceae. Mitosis is, however, atypical of both Prymnesiophyceae and Chrysophyceae, and if this picoplanktonic alga is to be retained in the Chrysophyceae it must be seen as a most unusual member.