FURTHER EVIDENCE FOR A MEMBRANE-BOUND ENDOSYMBIONT WITHIN THE DINOFLAGELLATE PERIDINIUM FOLIACEUM1

The fine structure of the binucleate, fucoxanthin-containing dinoflagellate Peridinium foliaceum (Stein) Biechler was re-examined for evidence of an endosymbiout. The eucaryotic nucleus, chloroplasts and associated ribosome-dense cytoplasm were separated by a single invaginating membrane from the rest of the dinoflagellate cell. The triple membrane-enclosed eyespot, mesocaryotic nucleus, trichocysts and accumulation bodies resided in the dinoflagellate cytoplasm. These observations suggest that P. foliaceum contains a membrane-bound endosymbiont, similar to that already described for the closely related species. P. balticum (Levander) Lemmermann.     

NUTRIENT REQUIREMENTS OF THE DINOFLAGELLATE PERIDINIUM GATUNENSE1

Optimum nutrient conditions for growth and photosynthesis of Peridinium gatunense (Nygaard) (Peridinium cinctum fa. westii) were investigated using axenic clones in batch cultures. Selenium (Se) had previously been found to be an indispensable growth factor for P. gatunense. Optimal, suboptimal, and supraoptimal concentrations of HCO₃^?, N, Ca, Cl, Mg, P, K, S, Si, EDTA-Na, Fe, Mo, Zn, Mn, Co, Se, B, Br, I, and various trace element mixtures were determined by measuring biomass development, growth rates, ¹⁴C uptake, and/or oxygen production at various concentration gradients of these elements. The general characteristics of the best formulation, medium-L 16, relative to other media, are its high content of NaHCO₃ (1 meq · L^?1) and Mo (0.2 μM) but low concentrations of NO_3-N (150 μM), PO_4-P (10 μM), and Fe (0.4 μM), in addition to its content of Se. The total content of trace metals, except for Se, may be reduced to one-fourth of that in medium-L 16 without altering the major growth-promoting properties of the medium. Medium-L 16 deviated considerably from Lake Kinneret (Israel) water, being much lower in macroelements except for N and P. The pH (8.1–8.4) was in the same range, but the values of conductivity (140 μS · cm^?1), alkalinity (1 meq · L^?1) and NaCl (200 μM) were > 8, 2, and 30 times higher, respectively, in the lake water. Selenium deficiency may limit the growth of P. gatunense in this lake.     

NUCLEAR BASIC PROTEINS FROM THE BINUCLEATE DINOFLAGELLATE PERIDINIUM FOLIACEUM (PYRROPHYTA)1

Histories of the endosymbiont nucleus of the binucleate dinoflagellate Peridinium foliaceum Stein were prepared from isolated nuclei and analyzed by peptide mapping, ammo acid composition, and two-dimensional gel electrophoresis. Using these criteria, we identified the presence of two HI-like histories and the core histones H3, H2A, H2B, and H4. These histones are similar but not identical to those of the endosymbiont nucleus of the bi-nucleate dinoflagellate Peridinium balticum Levander.     

CARBONIC ANHYDRASE ACTIVITY IN THE BLOOM-FORMING DINOFLAGELLATE PERIDINIUM GATUNENSE

The response of carbonic anhydrase (CA) activity in Peridinium gatunense Nygaard, the natural bloom-forming dinoflagellate in Lake Kinneret, to diel and seasonal variations in environmental conditions was characterized under controlled laboratory experiments. Simulated diel cycles demonstrated large changes in the ambient concentration of dissolved CO₂ and parallel changes in CA activity. The CA activity depended on the total concentrations of inorganic carbon (C₁) and in particular on the dissolved CO₂. Lowering the C₁ concentrations resulted in a large increase in CA activity within several hours. Light and photosynthesis were both required for the induction of CA activity. Under CO₂ -limited conditions, the dependence of the photosynthetic rate on CA (estimated from the ratio of photosynthetic rates in the presence or absence of CA inhibitors) was greater in P. gatunense than in other eukaryotic microalgae. This points to the ecological significance of CA in photosynthetic carbon uptake mechanisms of a large, dominant alga in a natural ecosystem .     

INTRASPECIFIC VARIATION IN THE DINOFLAGELLATE GAMBIERDIZSCUS TOXICUS (DINOPHYCEAE). I. ISOZYME ANALYSIS

Intraspecific variation among 19 isolates of the ciguatera-causing dinoflagellate Gambierdiscus toxicus Adachi & Fukuyo (Dinophyceae) collected from French Polynesia, New Caledonia, and the French West Indies was investigated by isozyme analysis. Comparison of their cell sizes and growth rates revealed that significant variation exists among these clones. Comparison of electrophoretic patterns for seven enzyme systems indicated that G. toxicus is comprised of numerous biochemically distinct strains. Isolates from Tubuai and Hao appeared to be the most distantly related. Tahitian strains of G. toxicus also showed a remarkably low degree of similarity with the Tubuai isolates. The latter, which were taken from the same locale in Tubuai, also exhibited highly heterogeneous electrophoretic Profiles when compared to each other, suggesting a multiclonal origin. The single isolate analyzed from the Atlantic Ocean was most closely related to Tahitian isolates, despite their geographic separation. Finally, no clear relationship was found between the electrophoretic profiles of these isolates and their capacity to produce ciguatoxic compounds .     

RESPONSE OF CATALASE ACTIVITY TO ENVIRONMENTAL STRESS IN THE FRESHWATER DINOFLAGELLATE PERIDINIUM GATUNENSE1

Catalase activity increased in Peridinium gatunense (formerly P. cinctum fa. westii) cells during the decline of the seasonal spring bloom period in Lake Kinneret. This was correlated with the low ambient total CO₂ concentration. The relationship was confirmed in laboratory experiments where maximum catalase activity occurred under an atmosphere composed of 30% O₂ and 0.003% CO₂. Conversely, high CO₂ concentrations inhibited catalase activity. The rise in catalase activity was not directly due to increasing environmental pH, as in vitro and in vivo measurements showed a characteristic broad pH curve with a constant activity from pH 6–10 for catalase. Photoinhibition of catalase occurred above 250 μmol photons · m^?2· s^?1. However, at high photoinactivating irradiances, photoinhibition was ameliorated under high pO₂/pCO₂. Such conditions prevail in the Kinneret at the end of the spring. We propose that the enhancement of photorespiration (under high pO₂/pCO₂) induces a temporary burst in catalase activity despite the progressively photoinhibitory conditions of early summer.     

ANTIOXIDATIVE PROTECTION OF PERIDINIUM GATUNENSE IN LAKE KINNERET: SEASONAL AND DAILY VARIATION1

A comprehensive antioxidative mechanism was found in the freshwater dinoflagellate Peridinium gatunense Lemm. during the spring bloom in Lake Kinneret. Ascorbate was present throughout the bloom period and was responsible, together with catalase, for the elimination of photosynthetically produced H₂O₂. As glutathione concentrations and ascorbate regenerative enzymes were negligible during mid-spring, ascorbate was presumably biosynthesized during the photosynthetically active period. Antioxidative activity increased overall at the end of the spring in conjunction with elevated ambient stress conditions, for example high light. Under such circumstances, ascorbate was regenerated. Ascorbate levels doubled when cells were exposed to an increase in irradiance from 60 to 600 μmol photons·m^?2·s^?1, and on addition of H₂O₂, concentrations increased a further 20-fold. Significant antioxidative activity was also noted in the dark, although this was dependent on the presence of H₂O₂. Diurnal changes in antioxidants and their regenerative enzymes were observed. The activities of mono-dehydroascorbate reductase, glutathione reductase, and ascorbate concentrations showed ultraradian periodicity and were completely in phase throughout the day/night period. Dehydroascorbate reductase activity and glutathione concentrations were also in phase but showed aperiodic variation, as did ascorbate peroxidase activity. Superoxide dismutase and catalase activities were generally out of phase during the 24-h period but did show ultraradian periodicity. Lake samples entrained under constant light revealed an inate 12-h rhythm for catalase activity, during at least 36 h.     

PIGMENTS OF THE DINOFLAGELLATE PERIDINIUM BALTICUM AND ITS PHOTOSYNTHETIC ENDOSYMBIONT1

An examination of the pigments of the binucleate dinoflagellate Peridinium balticum (Levander) Lemmerman revealed the presence of chlorophylls a, c₁ and c₂ and the carotenoids: fucoxanthin (most abundant), diadinoxanthin, diatoxanthin, an unidentified fucoxanthin-like xanthophyll, β-carotene, γ-carotene and astaxanthin. A comparison of the pigments of P. balticum and P. foliaceum (Stein) Biecheler, also a binucleate dinoflagellate, demonstrated similar compositions. However P. balticum lacked the β-carotene precursors (e.g. phytoene) which accumulated outside the chloroplast in P. foliaceum. This study indicates that P. balticum and P. foliaceum are closely related; each species is a heterotrophic dinoflagellate with a photosynthetic endosymbiont taxonomically affiliated with the Chrysophyta (Chrysophyceae or Bacillariophyceae).     

DISCRIMINATIVE POWER OF NUCLEAR rDNA SEQUENCES FOR THE DNA TAXONOMY OF THE DINOFLAGELLATE GENUS PERIDINIUM (DINOPHYCEAE)1

The genus Peridinium Ehrenb. comprises a group of highly diversified dinoflagellates. Their morphological taxonomy has been established over the last century. Here, we examined relationships within the genus Peridinium, including Peridinium bipes F. Stein sensu lato, based on a molecular phylogeny derived from nuclear rDNA sequences. Extensive rDNA analyses of nine selected Peridinium species showed that intraspecies genetic variation was considerably low, but interspecies genetic divergence was high (>1.5% dissimilarity in the nearly complete 18S sequence; >4.4% in the 28S rDNA D1/D2). The 18S and 28S rDNA Bayesian tree topologies showed that Peridinium species grouped according to their taxonomic positions and certain morphological characters (e.g., epithecal plate formula). Of these groups, the quinquecorne group (plate formula of 3′, 2a, 7″) diverged first, followed by the umbonatum group (4′, 2a, 7″) and polonicum group (4′, 1a, 7″). Peridinium species with a plate formula of 4′, 3a, 7″ diverged last. Thus, 18S and 28S rDNA D1/D2 sequences are informative about relationships among Peridinium species. Statistical analyses revealed that the 28S rDNA D1/D2 region had a significantly higher genetic divergence than the 18S rDNA region, suggesting that the former as DNA markers may be more suitable for sequence‐based delimitation of Peridinium. The rDNA sequences had sufficient discriminative power to separate P. bipes f. occultaum (Er. Lindem.) M. Lefèvre and P. bipes f. globosum Er. Lindem. into two distinct species, even though these taxa are morphologically only marginally discriminated by spines on antapical plates and the shape of red bodies during the generation of cysts. Our results suggest that 28S rDNA can be used for all Peridinium species to make species‐level taxonomic distinctions, allowing improved taxonomic classification of Peridinium.     

胶孢炭疽菌的种内遗传多样性研究*

应用RAPD分析对广东不同果树上的胶孢炭疽菌的种内遗传多样性进行研究。结果表明:除部分芒果上的菌株外,20个来源于不同果树上的胶孢炭疽菌都以较高的相似系数聚为一个大群(群I)。说明尽管胶孢炭疽菌具有复合种的性质,但在一定的地理范围内,其遗传背景还是相近的,表现出种的典型特征。6个芒果菌株组成3个小群,且与群I的亲缘关系较远,其分类地位有待进一步明确。     

EFFECT OF TEMPERATURE,LIGHT AND pH ON GROWTH,PHOTOSYNTHESIS AND RESPIRATION OF THE DINOFLAGELLATE PERIDINIUM CINCTUM FA. WESTII IN LABORATORY CULTURES1

Optimum light, temperature, and pH conditions for growth, photosynthetic, and respiratory activities of Peridinium cinctum fa. westii (Lemm.) Lef were investigated by using axenic clones in batch cultures. The results are discussed and compared with data from Lake Kinneret (Israel) where it produces heavy blooms in spring. Highest biomass development and growth rates occurred at ca. 23° C and ≥50 μE· m^?2·s¹ of fluorescent light with energy peaks at 440–575 and 665 nm. Photosynthetic oxygen release was more efficient in filtered light of blue (BG 12) and red (RG 2) than in green (VG 9) qualities. Photosynthetic oxygen production occurred at temperatures ranging from 5° to 32° C in white fluorescent light from 10 to 105 μE·m^?2·s^?1 with a gross maximum value of 1500 × 10^?12 g·cell^?1·h^?1 at the highest irradiance. The average respiration amounted to ca. 12% of the gross production and reached a maximum value of ca. 270·10^?12 g·cell^?1·h^?1 at 31° C. A comparison of photosynthetic and respiratory Q₁₀-values showed that in the upper temperature range the increase in gross production was only a third of the corresponding increase in respiration, although the gross production was at maximum. Short intermittent periods of dark (>7 min) before high light exposures from a halogen lamp greatly increased oxygen production. Depending on the physiological status of the alga, light saturation values were reached at 500–1000 μE·m^?2·s^?1 of halogen light with compensation points at 20–40 μE·m^?2·s^?1 and I_k-values at 100–200 μE·m^?2·s^?1. The corresponding values in fluorescent light in which it was cultured and adapted, were 25 to 75% lower indicating the ability of the alga to efficiently utilize varying light conditions, if the adaptation time is sufficient. Carbon fixation was most efficient at ca. pH 7, but the growth rates and biomass development were highest at pH 8.3.     

UTEX 1336: PERIDINIUM CINCTUM OR PERIDINIUM VOLZII (DINOPHYCEAE)?1

Plate pattern variation in UTEX clone 1336 and published photographs using this clone indicate the presence of two taxa: Peridinium cinctum and Peridinium volzii. All subclones established from UTEX 1336 contain the same two cell types. The identification of UTEX 1336 and its future use by researchers are discussed.     

SYNCHRONIZATION OF THE MARINE DINOFLAGELLATE AMPHIDINIUM CARTERI IN DENSE CULTURES1

Under improved conditions, Amphidinium carteri Hulburt can be obtained as dense cultures (5–9 × 10⁵ cells · ml^?1) 5 days after inoculation. The possible association of a marine bacterium with the alga is discussed. A method to synchronize this photosynthetic organism is described which is based on the endogenous rhythm of division and the effect of light-dark alternating periods.     

THE EFFECTS OF TEMPERATURE,IRRADIANCE, AND NITROGEN ON THE ENCYSTMENT AND GROWTH OF THE FRESHWATER DINOFLAGELLATES PERIDINIUM CINCTUM AND P. WILLEI IN CULTURE (DINOPHYCEAE)1

Effects of temperature, irradiance, and nitrogen availability on the encystment and growth of the freshwater dinoflagellates Peridinium cinctum Ehrenberg and Peridinium willei Huitfeld-Kaas were studied in culture. Lack of nitrogen was the main trigger of encystment in both species. Irradiance had a secondary effect on the percentage of the population of each species that encysted. Temperature did not significantly affect encystment in either species. In both species, only a small percentage of the population underwent encystment. Low light had an inhibitory effect on the growth of P. willei growing in nitrogen-sufficient medium.     

DEVELOPMENT OF THE ENDOPARASITIC DINOFLAGELLATE AMOEBOPHRYA CERATII WITHIN HOST DINOFLAGELLATE SPECIES1

The endoparasitic dinoflagellate Amoebophrya ceratii Koeppen occurs in coastal waters of Nova Scotia within cells of two dinoflagellate hosts, a Scrippsiella species (probably S. trochoidea (Stein) Loeb. III) and Dino-physis norvegica Claparede & Lachman. We describe the development of the endoparasitic stage (the trophont) of A. ceratii within host cells using light and electron microscopy. After entry into the host, the trophont grows and expands until most of the host cell is occupied by the parasite. Growth is marked by a proliferation of trophont nuclei and flagella and by the formation of numerous lobes, each of which possesses a characteristic dinoflagellate amphiesma. The mature endoparasitic trophont is recognized at the light microscopic level as a beehive-shaped structure that consists of numerous lobes of the developing motile sporont cells and a mastigocoel cavity containing the sporont flagella.     

广赤眼蜂滞育诱导中的种内变异及复寄生的作用(英语)

研究了采自伊朗不同害虫的两种广赤眼蜂种群(T.evanescens A和T.evanescens B)的滞育,在米蛾卵内用恒温8℃,5℃或变温(11-23)℃-11℃容易地诱导T.evanescens A进入稳定的滞育,但却不能用同样的温度和寄主诱导T.evanescens B进入滞育.试验表明,母代的寄主和避免复寄生的能力可能在广赤眼蜂滞育诱导种内变异中起重要作用.     

THE INFLUENCE OF INTRASPECIFIC VARIATION IN DISPERSAL STRATEGIES ON THE GENETIC STRUCTURE OF PLANTHOPPER POPULATIONS

The hypothesis that levels of gene flow among populations are correlated with dispersal ability has typically been tested by comparing gene flow among species that differ in dispersal abilities, an approach that potentially confounds dispersal ability with other species-specific differences. In this study, we take advantage of geographic variation in the dispersal strategies of two wing-dimorphic planthopper species, Prokelisia marginata and P. dolus, to examine for the first time whether levels of gene flow among populations are correlated with intraspecific variation in dispersal ability. We found that in both of these coastal salt marsh–inhabiting species, population-genetic subdivision, as assessed using allozyme electrophoresis, parallels geographic variation in the proportion of flight-capable adults (macropters) in a population; in regions where levels of macroptery are high, population genetic subdivision is less than in regions where levels of macroptery are low. We found no evidence that geographic variation in dispersal capability influences the degree to which gene flow declines with distance in either species. Thus, both species provided evidence that intraspecific variation in dispersal strategies influences the genetic structure of populations, and that this effect is manifested in population-genetic structure at the scale of large, coastal regions, rather than in genetic isolation by distance within a region. This conclusion was supported by interspecific comparisons revealing that: (1) population-genetic structure (G_ST) of the two Prokelisia species correlated negatively with the mean proportion of flight-capable adults within a region; and (2) there was no evidence that the degree of isolation by distance increased with decreasing dispersal capability. Populations of the relatively sedentary P. dolus clustered by geographic region (using Nei's distances), but this was not the case for the more mobile P. marginata. Furthermore, gene flow among the two major regions we surveyed (Atlantic and Gulf Coasts) has been substantial in P. marginata, but relatively less in P. dolus. The results for P. marginata suggest that differences in the dispersal strategies of Atlantic and Gulf Coast populations occur despite extensive gene flow. We argue that gene flow is biased from Atlantic to Gulf Coast populations, indicating that selection favoring a reduction in flight capability must be intense along the Gulf. Together, the results of this study provide the first rigorous evidence of a negative relationship within a species between dispersal ability and the genetic structure of populations. Furthermore, regional variation in dispersal ability is apparently maintained by selective differences that outweigh high levels of gene flow among regions.     

THE DINOFLAGELLATE TRANSVERSE FLAGELLUM: THREE-DIMENSIONAL RECONSTRUCTIONS FROM SERIAL SECTIONS1

Serial sections through in situ transverse flagella of the dinoflagellate Peridinium cinctum f. irregulatum (Lindem.) Lefévre are presented. Three-dimensional reconstructions based upon tangential and radial series show a helically coiled axoneme lying external to and distinct from an accessory strand. Hitherto undescribed vesicles within the expanded flagellar sheath are suggested to provide a decoupling effect between axoneme and strand. The flagellar axis bears two types of hair but anchoring threads between cingulum and flagellum have not been found. Functional and taxonomic implications of these observations are briefly discussed.     

ULTRASTRUCTURAL ASPECTS OF SEXUAL REPRODUCTION IN THE RED TIDE DINOFLAGELLATE GONYAULAX TAMARENSIS1

The marine dinoflagellate Gonyaulax tamarensis Lebour is best known for its propensity to form blooms known as red tides in coastal waters worldwide. This paper examines the sexual cycle of this organism using light and electron microscopy. Sexual reproduction begins with contact between thecate gametes which subsequently shed their thecae to fuse along their pellicular layers. Nuclear fusion occurs well after cytoplasmic fusion and is characterized by several distinctive features: a highly vesiculate nucleoplasm without microtubules; nucleoli and V-shaped chromosomes abut the nuclear envelope distal to the region of nuclear contact; and each chromosome possesses a longitudinal line, the central chromosomal axis. Fusion results in a planozygote with numerous cytoplasmic storage products and a slightly thickened layer beneath the pellicle. Subsequent loss of thecal plates and a thickening of the sub-pellicular layer results in a non-motile hypnozygote. A newly-formed hypnozygote possesses numerous minute papillae along its outer surface, formed by the up-folding of the accumulating wall layer. Maturation of the hypnozygote wall results in a smooth three-layered wall, the outermost layer of which is the pellicular layer. Hypnozygote germination produces a large quadriflagellate plan-omeiocyte with a single nucleus and thecal plates identical to vegetative cells. Two subsequent divisions, presumably meiotic, result in Jour cells morphologically identical to vegetative cells.     

双角多甲藻有性生殖及厚垣合子形成条件的研究

双角多甲藻在MCV合成培养基中的最短加倍时间约6天,其有性生殖可用缺氮培养基进行诱导。批量培养的迟滞期和指数生长期末细胞的诱导效率最高,合子产率可达70％。厚垣合子形成的最适温度为19℃、pH7.4、光强5200lx。在鉴定的70个克隆藻株中,有2株为同宗配合;48株为异宗配合,其中“+”株23个,“-”株25个;其余20株未能诱导出有性生殖。合子开始萌发时,在中层壁和内层壁之间的空间出现1至多个“管状结构”,协助原生质体将合子壁顶破,外包一层薄壁的原生质体放出。