Peridinin—chlorophyll a proteins from the symbiotic dinoflagellate Symbiodinium (= Gymnodinium ) microadriaticum , Freudenthal

The conformers of peridinin–chorophyll a proteins (PCP), isolated from various strains of the symbiotic dinoflagellate Symbiodinium ( = Gymnodinium ) microadriaticum and analysed by isoelectric focusing in polyacrylamide gels, exhibited different patterns. In most instances the same pattern of conformers was found in each strain when freshly isolated from their respective hosts, after culture, and in two instances also after cloning. These observations suggest that characteristic patterns of PCP are diagnostic of particular strains of S . microadriaticum . Evidence is presented that generally the patterns do not change with environment. Analysis of PCP could potentially serve as a tool for the identification of strains of S . microadriaticum and could also serve as a marker for the empirical analysis of sexual recombination.

Rhythmic variations in calcification and photosynthesis associated with the coral Acropora cervicornis (Lamarck)

Large populations of the algal endosymbiont, Gymnodinium microadriaticum , occur in the tissues of Acropora cervicornis , and most other species of hermatypic corals. Symbiont photosynthesis is directly proportional to light-enhanced calcification by the coral. Fresh isolates of G. microadriaticum exhibit daily rhythms in photosynthetic efficiency at saturating and subsaturating irradiation. With ambient solar irradia­tion, photosynthetic maxima occur at sunrise and sunset, and a minimum occurs at local solar noon. These rhythms provide an important homeostatic mechanism which enables A. cervicornis to maximize the portion of each day during which calcification can occur at a relatively high constant rate.

Ultrastructure and Lipid Composition of Zooxanthellae from Tridacna maxima

Isolation of zooxanthellae (Gymnodinium microadriaticum) from clam tissue does not result in any loss of the outer limiting layers and the ultrastructure of the cell is similar to that of zooxanthellae found in other clams and corals. The major lipid components of G. microadriaticum are galactosyldiacylglycerols which comprise about 50% of the extractable lipid. The major fatty acids present are palmitic, γ-linolenic and octadecatetraenoic acids, together with a component identified as octadecapentaenoic acid. The presence of γ-linolenic acid is more representative of animal lipids than of plant lipids and there is a possibility that growth of the zooxanthella in a host tissue can affect the fatty acid composition.

Photosystem II in Symbiotic Algae

Symbiotic brown algae (zooxanthellae), Gymnodinium microadriaticum (= Symbiodinium microadriaticum), were isolated from the coral polyp Pocillopora damicornis and from the mantle of the clam Hippopus hippopus collected from coral reefs near Lizard Island on the Great Barrier Reef. Passage of the coral and clam zooxanthellae through a Yeda Press at 2000 and 21 000 p.s.i., respectively, yielded preparations of chloroplast lamellae with the ratio of chlorophyll α to chlorophyll c ranging from 0.95 to 1.2. The chloroplast preparations photoreduced 2,6-dichlorophenolindophenol (DCPIP) at rates of 1.66 (coral zooxanthellae chloroplasts) and 1.96 (clam zooxanthellae chloroplasts) micromoles DCPIP reduced per minute per milligram total chlorophyll in white light. Rates were 30-50% lower in red light. The photoreduction was inhibited more than 99% by 2.5 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea. Comparisons made with maize chloroplasts indicated that the clam zooxanthellae chloroplasts required only slightly higher light intensities for maximum rates of photoreduction of DCPIP than the grana-containing maize mesophyll chloroplasts. The coral zooxanthellae chloroplasts required a still higher light intensity for near saturation of the photoreduction of DCPIP, but not as high as that required by maize bundle sheath chloroplasts. Chloroplasts prepared from green algae isolated from the tissues of a tunicate of unknown species also photoreduced DCPIP but at low rates. Light saturation for the reaction was attained at around the same intensity as for the clam zooxanthellae chloroplasts. Based on the photosynthetic rate of zooxanthellae isolated from the clam Tridacna maxima and the number of cells contained in the mantle, it was concluded that the photosynthetic potential of the mantle of T. maxima, on either a chlorophyll or area basis, was about the same as that of a leaf of a C3 plant.