PHOTOSYNTHETIC PIGMENTS IN FIFTY‐ONE SPECIES OF MARINE DIATOMS¹

Abstract

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 c 2 and 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 c 2 was present in all the diatoms tested and occurred together with chlorophyll c 1 in 88% of them. The presence of both chlorophylls c 1 and c 2 therefore can no longer be considered a universal characteristic of the diatom class. Where chlorophyll c 1 was absent or occurred in trace amounts only (8 species, 11 isolates), it was usually replaced by a new chlorophyll c pigment designated chlorophyll c 3 , recently characterized from several prymnesiophytes and one chrysophyte. Exceptions were Nitzschia closterium (CS‐114), which contained only chlorophyll c 2 , and Nitzschia bilobata (CS‐47), which contained all three chlorophylls (c 1 , c 2 and c 3 ) in approximately equal amounts. Five species that contained chlorophylls c 1 and c 2 also contained chlorophyll c 3 in trace quantities Quantitative pigment analyses of the 71 isolates showed that chlorophyll concentrations ranged from 0.02 μg. 10 6 cells −1 in the smallest diatom, Extubocellulus spinifer , to 174.4 μg. 10 6 cells −1 in one of the largest diatoms, Coscinodiscus sp. under the standard growth conditions used. The mean molar ratio of chlorophyll a:c in 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 c 1 and c 2 and‘true’fucoxanthin, species with chlorophylls c 3 and c 2 and‘true’fucoxanthin, and species with chlorophylls c 3 and c 2 and fucoxanthin derivatives.