PHOTOSYNTHETIC PIGMENTS IN FIFTY‐ONE SPECIES OF MARINE DIATOMS1

ABSTRACT The photosynthetic pigments of 51 species (71 isolates) of tropical and sub‐tropical diatoms from 13 out of 22 families were examined. These were the Thalassiosiraceae, Melosiraceae, Coscinodiscaceae, Rhizosoleniaceae, Biddulphiaceae, Chaetoceraceae, Lithodesmiaceae, Eupodiscaceae, Cymatosiraceae, Diatomaceae, Naviculaceae, Nitzschiaceae and Phaeodactylinaceae. Pigments were analyzed by cellulose and polyethylene thin‐layer chromatography (TLC) and reverse‐phase high‐performance thin‐layer chromatography (HPTLC). All species contained chlorophylls a and c2and the carotenoids carotene, fucoxanthin, diatoxanthin and diadinoxanthin. In addition, 14 species (20 isolates) contained one or more of four minor carotenoids, which were not identified further. One species,Thalassiothrix heteromorpha, contained small amounts of a 19′‐butanoyloxyfucoxanthin‐like pigment, in addition to fucoxanthin. Chlorophyll c2was present in all the diatoms tested and occurred together with chlorophyll c1in 88% of them. The presence of both chlorophylls c1and c2therefore can no longer be considered a universal characteristic of the diatom class. Where chlorophyll c1was absent or occurred in trace amounts only (8 species, 11 isolates), it was usually replaced by a new chlorophyll c pigment designated chlorophyll c3, recently characterized from several prymnesiophytes and one chrysophyte. Exceptions wereNitzschia closterium(CS‐114), which contained only chlorophyll c2, andNitzschia bilobata(CS‐47), which contained all three chlorophylls (c1, c2and c3) in approximately equal amounts. Five species that contained chlorophylls c1and c2also contained chlorophyll c3in trace quantities Quantitative pigment analyses of the 71 isolates showed that chlorophyll concentrations ranged from 0.02 μg. 106cells−1in the smallest diatom,Extubocellulus spinifer, to 174.4 μg. 106cells−1in one of the largest diatoms,Coscinodiscussp. under the standard growth conditions used. The mean molar ratio of chlorophylla:cin the 72 isolates was 3.33, with a range of 1.65–7.25. The close similarity between diatom and prymnesiophyte pigmentation was confirmed. Each class has three patterns of pigmentation: viz species with chlorophylls c1and c2and‘true’fucoxanthin, species with chlorophylls c3and c2and‘true’fucoxanthin, and species with chlorophylls c3and c2and fucoxanthin derivatives.