Effects of Indoleamines and Short Photoperiods on the Encystment of Gonyaulax polyedra

At a temperature of 15^oC, Gonyaulax polyedra responds to short days (light ≤ 10 h) by transition to the stage of a resting cyst. At 20^oC, even an lightdark (LD) cycle of 6:18 is incapable of inducing this process. In otherwise cyst-inducing conditions (15^oC; 10 h of light per day), an interruption of the scotophase by 2 h of light (LDLD 8:2:2:12 or 2:2:8:12) prevented encystment. Cyst induction is, therefore, initiated by a photoperiodic mechanism rather than by light deficiency. In Gonyaulax, photoperiodism may be mediated by the action of indoleamines. Melatonin, which exhibits a circadian rhythmicity in this organism, leads to encystment when given 1 h before lights-off in LD 11:13 at 15^oC, i.e., under otherwise noninducing conditions. Again, at 20^oC, melatonin is inefficient. Some analogues of melatonin, in particular, 5-methoxytryptamine and N,N-dimethyl-5-methoxytryptamine, and, at high concentrations, their respective precursors, serotonin and bufotenin, are capable of inducing cyst formation at 20^oC and in LD 12:12, whereas A'-acetyl-serotonin does not show this effect.     

Circadian Rhythm of Total Protein Synthesis in the Cytoplasm and Chloroplasts of Gonyaulaxpolyedra

Protein synthesis of Gonyaulax polyedra was analyzed by means of electron microscopic autoradiographs under constant conditions at different times of the 24-hr cycle. Circadian rhythmic changes in the synthesis rate of total protein were determined in the cytoplasm and chloroplasts of growing cells. Three independent series of experiments in constant light showed a maximum of grains per unit area during the 'subjective' dark phase (=phase that corresponds to the dark phase during a 12:12 hr LD cycle) in both compartments. Minimum and maximum grain number are different by a factor of 5-10. The maximum of total protein synthesis coincided with the maximum phase shift by cycloheximide pulses (1) suggesting protein species within the total pool involved in the mechanism of the circadian clock. A similar rhythm of lower amplitude was observed in the mitochondria, but this rhythm cannot with certainty be attributed to these organelles. In a slowly growing culture a rhythm of total protein synthesis was observed that showed a smaller amplitude and a different phasing.     

COMPARISON OF TOXINS IN THREE ISOLATES OF GONYAULAX TAMARENSIS (DINOPHYCEAE)1

Toxicity levels and profiles of three isolates of Gonyaulax tamarensis Lebour grown under the same conditions were compared. One isolate was collected from Ipswich, Massachusetts, during the massive red tide of 1972 along the New England coast. The other two isolates were obtained from Perch Pond (Falmouth, Massachusetts) and Mill Pond (Orleans, Massachusetts) located in the southwest and south of Cape Cod, Massachusetts, respectively. All the three cultures produced toxins with variation in their toxicity levels. Toxin contents were highest in the Ipswich isolate, followed in an order by Mill Pond and Perch Pond cultures. Morphological similarity existed between Ipswich and Mill Pond cells, whereas the Perch Pond cells possessed an additional ventral pore on the l' epithecal plate.     

A Circadian Rhythm in the Activity of Superoxide Dismutase in the Photosynthetic Alga Gonyaulax polyedra

The activity of superoxide dismutase in cell-free extracts of Gonyaulax made at different times of day and night was found to be three to four times higher during the day. This rhythm continued in cells kept in constant light, indicating that the regulation can be attributed to the cellular circadian clock.     

Ultrastructural characterization of asexual cysts ofGonyaulax polyedra Stein (Dinoflagellata)

Summary In the bioluminescent dinoflagellateGonyaulax polyedra, the formation of asexual cysts was elicited either by addition of 5-methoxytryptamine or by transfer to short-day conditions under lower temperature and decreased light intensity. The resulting changes were followed in vivo by light microscopy, and analysed ultrastructurally by electron microscopy. Irrespective of the method of cyst induction, theca and flagella shedding and the formation of a cyst wall can always be observed as essential steps in this process. Despite the extremely low level of bioluminescence emitted from the cysts, some scintillons persist. Encystment is accompanied by organelle and substructure rearrangement. Although cysts induced by 5-methoxytryptamine or by short days closely resemble each other, electron microscopy reveals typical differences. In cysts obtained by treatment with 5-methoxytryptamine most chloroplasts are of the expanded type, extending to the central region, whereas only a few are compact and peripherally positioned. Cysts induced by shortdays predominantly contain chloroplasts of the compact type and contain large amounts of stored starch and lipids. Their ultrastructural organization therefore resembles that of mastigote cells during darkness.     

THE PATH OF CARBON IN PHOTOSYNTHESIS BY MARINE PHYTOPLANKTON12

Using cultures of a number of different marine algae (diatoms Skeletonema costatum (Grev.) Cleve and Phaeodactylum tricornutum Bohlin, chrysophyte Isochrysis galbana Parke, green flagellate Dunaliella tertiolecta Butcher, dinoflagellate Gonyaulax tamarensis Lebour) the short-term, pattern of ¹⁴CO₂ assimilation has been investigated. In all except D. tertiolecta the labelling of amino acids and intermediates of the tricarboxylic acid (Krebs) cycle was significantly heavier than that of sugar phosphates. Over periods of 30–120 s labelling in amino acids and Krebs cycle intermediates accounted for 41–95% of the ¹⁴C fixed (depending on the alga). Over shorter times (< 10 s) the pattern in the 2 diatoms showed significant labelling of C₄ acids (and related com-pounds) and little labelling of sugar phosphates. The reverse wits seen with D. tertiolecta. Also, in the 2 diatoms and in G. tamarensis significant inhibition of photosynthesis by oxygen could only be achieved with 100% oxygen; atmospheric levels having little effect. Parallel measurements of 2 carboxylating enzymes showed that ribulose-1,5-diphosphate carboxylase (RuDPCase) was significantly greater than phospho (enol)pyruvate carboxylase (PEPCase) activity only in the green flagellate. It is suggested that photosynthesis in marine diatoms depends on an active PEPCase utilizing bicarbonate as a substrate and that a less active RuDPCase utilizes CO₂. In D. tertiolecta the pattern more closely resembles that of a “Calvin (C₃)” plant. The dinoflagellate and the chrysophyte appeared to show a mixed C₃ and C₄ photosynthesis.     

Species-specific probe, based on 18S rDNA sequence, could be used for identification of the mucilage producer microalga Gonyaulax fragilis (Dinophyta)

In the Adriatic Sea, the correlation between mucilage phenomena and the presence of Gonyaulax fragilis (Schütt) Kofoid (Dinophyta) has been recently demonstrated. The application of PCR-based methods and the development of species-specific molecular probes might represent powerful technologies for rapid and specific monitoring of microalgal species in seawater samples. Here, we report sequencing of the small subunit (SSU) ribosomal RNA gene (18S rDNA) of G. fragilis and its comparative analysis within the Dinophyta. Total DNAs were extracted and amplified from cultured cells of G. fragilis, which were isolated from natural phytoplanktonic association in the northern Adriatic Sea. Total 18S rDNA gene was amplified using 16S1N and 16S2N primers and sequenced using ad hoc designed internal primers. The primers amplified a product of expected size (length 1700/1800 bp). The phylogenetic analysis carried out by comparing G. fragilis sequence to homologous sequences of Lingulodinium polyedrum (Stein) Dodge, Gonyaulax spinifera (Claparède et Lachmann) Diesing, Protoceratium reticulatum (Claparède et Lachmann) Bütschli revealed a great nucleotide divergence of G. fragilis SSU sequence. Therefore, the SSU sequence could be used as species-specific marker for the identification of this mucilage producer microalga. In addition, such sequence could be used as target to design oligonucleotide probes for the construction of DNA microchips as diagnostic tool for the routine monitoring of harmful algae in seawater. An erratum to this article is available at .