Circadian communication between unicells?

Populations ofGonyaulax polyedra, in two different phases, about 11 h apart, were mixed, and the intensity of their spontaneous bioluminescence glow recorded for about 2 wk under conditions of constant dim (35±3 μE/m²/s) white light and constant temperature (19.0±0.3°C). The phases and amplitudes of glow signals recorded from mixed cultures were compared with those obtained from the arithmetic sum of the intensity data from two control vials. Peaks in control cultures generally remained separate, but there was a spontaneous increase in the period beginning 6–11 d after the onset of constant conditions. This did not occur in cultures in which the medium was exchanged with fresh medium every 2 d. In the actual mixes of two cultures there was a merging of the two subpeaks in the signal, which did not occur when the medium was exchanged. The results indicate that conditioning of the medium by cells may affect the period of the circadian rhythm and that this might result in a type of communication. Supported by the Deutsche Forschungsgemeinschaft; present address     

SEXUAL REPRODUCTION IN THE TOXIC DINOFLAGELLATE GONYAULAX MONILATA1

The sexual cycle of Gonyaulax monilata Howell was observed in stationary cultures and in nitrogen-deficient medium. The armored, isogamous gametes fuse in a characteristic manner with cingula at oblique angles. Nuclear fusion lags slightly behind cytoplasmic fusion. The zygote enlarges for several days. The dark, double-flagellated planozygote encysts within 1–3 wk. Early hypnozygotes are round to ovoid and contain lipid and one or two large golden-yellow globules. As the hypnozygote matures, the globules become smaller and the cytoplasm darkens and pulls from the wall. All cysts examined contained only one nucleus. A very dark, uninucleate post-hypnozygotic cell escapes through an archeopyle and within 24 h divides into daughter cells which divide in 24–48 h forming a small chain. The production of thick walled zygates in culture implies that such resting stages in marine sediments could serve as a source stock for blooms. This species causes toxic red tides and the existence of benthic “seed beds” consisting of hypnozygotes is now plausible.     

Cell Division in Gonyaulax catenella,A Marine Catenate Dinoflagellate*

Mitosis and cytokinesis are described and illustrated for the first time in the mesokaryotic, catenate dinoflagellate Gonyaulax catenella. A structure similar to the central body of G. tamarensis and G. monilata is shown by light and electron microscopy to be situated intranuclearly near the arms of the U-shaped interphase nucleus, and is suggested to function in the segregation of daughter chromosomes. This structure has the fine structure of a nucleolus, and it is suggested that the term central body be replaced by persistent nucleolus (= endosome). The time required for the completion of mitosis is 4–6 hr, while cytokinesis requires at least 2 hr. Cytokinesis begins during the mitotic cycle, and the plane of fission is perpendicular to the mitotic plane of division. Parental fission moieties are retained and shared by the daughter cells while either a new antero-sinistral moiety or a posterodextral moiety is synthesized by the dividing cell.     

The occurrence of Gonyaulax tamarensis Lebour bloom in the Adriatic Sea along the coast of Emilia-Romagna

Abstract

The authors describe the occurrence of Gonyaulax tamarensis Lebour bloom in the Adriatic Sea between 200 and 1000 m off the coast of Emilia-Romagna during the period of August 14-20 1982.     

ADAPTATION OF CERATIUM FURCA AND GONYAULAX POLYEDRA (DINOPHYCEACE) TO DIFFERENT TEMPERATURES AND IRRADIANCES: GROWTH RATES AND CELL VOLUMES1

Growth rates and cell volumes of Ceratium furca Ehrenberg and Gonyaulax polyedra Stein were determined during the log phase of growth in cultures which had been extensively adapted to one of three temperatures and five irradiances. At each temperature, curves for the growth rate vs. irradiance for both species had light-limited and light-saturated regions. Three properties of these curves characterized the response of each species to temperature: the light-saturated growth rate, the irradiance at which growth became light-saturated and the compensation irradiance for growth. For both species, the first two properties generally decreased with declining growth temperature, while the compensation irradiance declined for Ceratium but had a V-shaped response pattern for Gonyaulax. The light-saturated growth rates were generally higher for Ceratium than for Gonyaulax, while the irradiance at which growth became saturated and the compensation irradiance were lower for Ceratium. The changes in cell volume associated with the irradiance and temperature of growth were very different for Ceratium and Gonyaulax. The cell size of Gonyaulax increased as irradiance and temperature decreased, while cell volumes of Ceratium did not change with temperature but were smallest at the highest and lowest growth irradiances. In general, the growth rate patterns were similar for Ceratium and Gonyaulax, while those for cell size were different. The maximum growth rate, the irradiance at which growth became saturated, the compensation irradiance, and the cell volume all showed that Ceratium grew at the same rate or faster than Gonyaulax over the entire range of irradiances and temperatures examined.     

WIDESPREAD PHAGOCYTOSIS OF CILIATES AND OTHER PROTISTS BY MARINE MIXOTROPHIC AND HETEROTROPHIC THECATE DINOFLAGELLATES1

An electron microscopic examination of large amorphous inclusions located in a variety of photosynthetic thecate dinoflagellates (Alexandrium ostenfeldii (Paulsen) Balech et Tangen, Gonyaulax diegensis Kofoid, Scrippsiella sp., Ceratium longipes (Bailey) Gran, and Prorocentrum micans Ehrenberg) and a nonphotosynthetic thecate species (Amylax sp.) revealed each inclusion to be a food vacuole, the majority of which were ingested ciliate prey. Recognizable features of these ciliates included linear arrays of basal bodies and cilia consistent with oligotrich polykinetid structure, characteristic macronuclei, chloroplasts (evidently kleptoplastids), cup-shaped starch plates, and cylindrical extrusomes. Three species contained (apparent) nonciliate prey: Scrippsiella sp., whose food vacuoles consistently contained unusual and complex extrusome-like cylindrical bodies having a distinctive six-lobed, multilayered structure; P. micans, which contained an unidentified encysted cell; and a single A. ostenfeldii cell, containing a Dinophysis sp. dinoflagellate cell. Several food vacuoles of ciliate origin had a red hue. This, together with the resemblance of A. ostenfeldii cells to planozygotes, suggests that similar structures previously identified as accumulation bodies may in fact be food vacuoles and that feeding may in some cases be associated with sexual processes.     

EFFECTS OF SMALL-SCALE TURBULENCE ON PHOTOSYNTHESIS,PIGMENTATION, CELL DIVISION,AND CELL SIZE IN THE MARINE DINOFLAGELLATE GOMAULAX POLYEDRA (DINOPHYCEAE)1

Several experiments were conducted to understand better the physiological mechanisms underlying growth inhibition of the dinoflagellate Gonyaulax polyedra Stein due to small-scale turbulence shear. To measure photosynthetic ¹⁴C uptake, a “phytoplankton wheel” device for rotating cultures in closed bottles was used. Turbulence was quantified biologically in the bottles by comparing growth inhibition with that in cultures with constant shear between a fixed cylinder and an outer concentric rotating cylinder (a stable Couette flow). At saturating irradiances, particulate photosynthesis (P_sat) or photosynthesis per unit chlorophyll (P^B_sat) were not inhibited completely at the highest turbulence level (26.6 rad.s^?1), and photosynthesis was less sensitive than growth. Photosynthesis per cell (P^C_sat) was increased by turbulence. In three experiments on the effects of turbulence on photosynthesis versus irradiance curves, the slope of the curve, α, for particulate photosynthesis at limiting irradiances did not change. Photosynthesis per unit chlorophyll per unit irradiance (α^B) decreased at high (but not intermediate) turbulence levels. Photosynthesis per cell per unit irradiance, α^C, increased with turbulence, suggesting an increase in photosynthetic efficiency in turbulent cultures. In two of the three experiments, respiration rates increased with turbulence, and in one experiment excretion of photosynthetically fixed ¹⁴C was not affected by motion. Ratios of accessory pigments to chlorophyll a did not change with turbulence, but pigments per cell and per dry weight increased with turbulence. These findings suggest little or no disruption of the photosynthetic apparatus. When turbulence was applied for 1 week, β-carotene increased while peridinin and diadinoxanthin decreased, suggesting inhibition of synthesis of these latter pigments by prolonged turbulence. Since cell numbers did not increase or decreased during turbulent 72–h incubations, cell division was inhibited and also the cells were very much enlarged. Increases in α^C per cell suggest that, in the sea, photo synthetic metabolism can persist efficiently without cell division during turbulent episodes. After turbulence ceases or reaches low levels again, cells can then divide and blooms may form. Thus, blooms can come or go fairly rapidly in the ocean depending on the degree of wave- and wind-induced turbulence.     

COEXLSTENCE OF TOXIC AND NONTOXIC DINOKLAGELLAIES RESEMBLING GQNYAULAX TAMARENSIS IN NEW ENCILAND COASTAL WATERS (NW ATLANTIC)1

Two forms resembling Gonyaulax tamarrensis Lebour coexist in Maine cosat plankton; one is toxic, the other is nontoxic. At times, red patches of dinoflagellates were identified as G. tamarensis, yet only presumed to he toxic. Toxic froms were found in June, July 1975 and 1976. The nontoxic form was found in a more esraurine area, e.g., mid-July 1975, early July 1976. These two forms are not easily distinguished by conventional microncopic ohservation, nor by pigment analysis. Preliminary observations suggest that the nontoxic form is smaller than G. excavata (Braarud) Balech and tacks the “excavated” ventrat region. Characteristic G. excavata resting cysts were found in sediment from the shellfish toxic area off Newagen and Monhegan (Maine) and were not found in sediments from areas where the nontoxic form bloomed. There appear to be a minimum of two G. tamarensis-like organisms. Full systematic treatment of these must await further information.     

THECAL ULTRASTRUCTURE OF THE TOXIC MARINE DINOFLAGELLATE GONYAULAX CATENELLA1

The toxic marine dinoflagellate Gonyaulax catenella Whedon & Kofoid was studied with scanning and transmission electron microscopy to describe the thecal morphology and to accurately define the taxonomic characters of the species. The closing platelet which lies in a U-shaped apical pore was revealed to be disassociable from a partly obscured apical platelet. Two previously unreported sulcal plates were charaterized and described. The entire complement of thecal plates numbered 33.     

USE OF THE CRICKET ACHETA DOMESTICA L. AS A BIOASSAY ORGANISM FOR THE TOXIC EXTRACT FROM GONYAULAX MONILATA (DINOPHYCEAE)1

A toxic extract from unialgal cultures, of Gonyaulax monilata Howell was tested for insecticidal activity on the cricket Acheta domestica L The regression line of the activity was compared with that of ouabain in this insect as well as with that of the toxic extract in mice. Although mice are approximately 2.5°as sensitive as the cricket an a body weight basis, because of the insect's smaller mass‘(1/50 that of the mouse), one can treat 26° as many crickets with the same amount of toxic material. This fact, coupled with the simple rearing requirements of the insect, makes it an ideal bioassay organism as well as a useful subject far further investigations of the physiological properties of the toxic extract and other bioactive compounds available in limited quantities.