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1.
Runar Thyrhaug Aud Larsen Corina P. D. Brussaard Gunnar Bratbak 《Journal of phycology》2002,38(2):338-343
In this study we investigated virus production in two marine phytoplankton species and how it relates to the host's cell cycle. Phaeocystis pouchetii (Hariot) Lagerheim and Pyramimonas orientalis McFadden, Hill & Wetherby, growing synchronously in batch cultures, were infected with their respective viruses (PpV and PoV) at four different stages in the cell cycle and the production of free virus was then measured for 30 h. The virus production in P. orientalis infected with PoV depended on the time of infection, whereas no such relation was found for P. pouchetii infected with PpV. The P. orientalis cultures infected at the end of the dark period and at the beginning of the light period produced three times more virus than those infected in the middle of the light period and eight times more virus than those infected at the beginning of the dark period. The latent periods for PpV and PoV were 12–14 h and 18–20 h, respectively, and in both cases were independent of the host cell cycle. The differences in virus production may be attributed to light or cell cycle dependent regulation of host infection, metabolism, or burst size. Regardless of the mechanism, these differences may be related to differences in the ecological strategies of the hosts and their ability to form blooms. 相似文献
2.
A new punctate species of Pyramimonas Schmarda from South Africa is described. This species is somewhat anomalous and, like P. chlorina Sym et Pienaar (subgenus Pyramimonas McFadden), has characters that bridge the divide between the subgenera Pyramimonas and Punctatae McFadden. Features of these two species, together with the lack of exclusive character sets for either subgenus derived from other species of these subgenera, lead to the conclusion that Punctatae now should be subsumed formally into the subgenus Pyramimonas. 相似文献
3.
Reserve products isolated from three species of prasinophycean algae: Pyramimonas parkeae Norris and Pearson, Pyramimonas amylifera Conrad and Platymonas tetrathele West were compared. Three pieces of experimental evidence indicate that the reserve product of each of the species analyzed is a true starch. (I) There is no essential difference between the light absorption curve for the complex formed between corn starch and iodine and the corresponding curves for the algal products. (2) The β-amylase breakdown limit of these compounds is very close to that of corn starch. (3) The X-ray diffraction diagrams produced by the reserve material from Pyramimonas parkeae and Platymonas tetrathele is a so-called A-spectrum characteristic of cereal starches while the diagram produced by grains from Pyramimonas amylifera corresponds to the B-spectrum typical for tuber starches. The dissimilarity between the X-ray diagrams produced by the starches from the Pyramimonas species suggests that a re-examination of the taxonomy of these species is warranted. 相似文献
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A vestigiferan species commonly referred to as Pyramimonas obovata N. Carter has been redescribed as P. melkonianii sp, nov. Characters of this species and a further six (P. disomata Butcher ex McFadden, Hill et Wetherbee, P. mantoniae Moestrup et Hill, P. mitra Moestrup et Hill. P. moestrupii McFadden, P. aff. nephroidea McFadden, P. orientalis Butcher ex McFadden, Hill et Wetherbee) isolated from South African waters are used to define further the subgenus Vestigifera McFadden. This includes a unique chloroplast shape and basal hyaline region with stellate or cruciform vacuoles, a transitional plate-like structure in the flagellum, and a different microtubular root system. The proximal set of basal body connectives were found to be remarkably symmetrical and like those of the subgenus Trichocystis McFadden, and a duct fibre was found associated with the Id root in all currently investigated species. The validity of the larger body (box and crown) scales as taxonomic markers at a fine level is also questioned. 相似文献
6.
Anchittha Satjarak John A. Burns Eunsoo Kim Linda E. Graham 《Journal of phycology》2017,53(3):601-615
Mitochondria are archetypal eukaryotic organelles that were acquired by endosymbiosis of an ancient species of alpha‐proteobacteria by the last eukaryotic common ancestor. The genetic information contained within the mitochondrial genome has been an important source of information for resolving relationships among eukaryotic taxa. In this study, we utilized mitochondrial and chloroplast genomes to explore relationships among prasinophytes. Prasinophytes are represented by diverse early‐diverging green algae whose physical structures and genomes have the potential to elucidate the traits of the last common ancestor of the Viridiplantae (or Chloroplastida). We constructed de novo mitochondrial genomes for two prasinophyte algal species, Pyramimonas parkeae and Cymbomonas tetramitiformis, representing the prasinophyte clade. Comparisons of genome structure and gene order between these species and to those of other prasinophytes revealed that the mitochondrial genomes of P. parkeae and C. tetramitiformis are more similar to each other than to other prasinophytes, consistent with other molecular inferences of the close relationship between these two species. Phylogenetic analyses using the inferred amino acid sequences of mitochondrial and chloroplast protein‐coding genes resolved a clade consisting of P. parkeae and C. tetramitiformis; and this group (representing the prasinophyte clade I) branched with the clade II, consistent with previous studies based on the use of nuclear gene markers. 相似文献
7.
Diel changes in mean cell volume, cellular carbon (carbon content per cell), cellular Chl a, C/N ratio, Chl a/carbon ratio and pigment composition were determined for an axenic clonal culture of Pyramimonas parkeae Norris et Pearson through three 12:12 h LD cycles in a laboratory culture tank of 1 m3. Mean cell volume and cellular C, N and most pigments increased during the light period as a result of photosynthesis and decreased with an increase in cell density by phased cell division during the dark period. Chi a and Chi b increased in a parallel manner during the light period. Increases in the diel synthesis pattern of carotenoids varied. Violaxanthin and lutein content increased for a few hours at the beginning of the light period and preceeded that of neoxanthin. The diel synthesis pattern of neoxanthin was similar to that of Chi a. Increases of loroxanthin and its ester form were slower than that of Chi a at the beginning of the light period. A net increase of α-carotene was observed during the dark period. Mass spectroscopy of carotenoid structure showed a new xanthophyll, loroxanthin dodecenoate, in this species. 相似文献
8.
Pyramimonas mucifera sp. nov., a punctate species of the genus, is unusual both behaviorally and at the fine structural level. It forms two distinct populations in culture, one benthic and one planktonic. Planktonic forms are more conventional for the genus, but benthic forms are found in loosely packed mucilage, have flagellar rather than ciliary beating of the flagella, and display a higher degree of metaboly. Ultrastructurally this species is unusual in that it has a unique scale complement and the cells contain numerous muciferous vesicles, leaving only small pockets of cytoplasm containing the usual organelles. This species has a 3–1 type flagellar apparatus but has an additional fibrillar band, a 4–3-2–3 microtubular root system and a flexible synistosome. The discovery of a mucilage-producing species of Pyramimonas draws attention to possible links with other prasinophytes (Halosphaera) and green algae of questionable affiliation (Oltmannsiellopsis and Hafniomonas). It also provides a model of the primitive pyramimonad. 相似文献
9.
During a summer cruise to the Ross Sea (Antarctica) areas of snow‐covered sea ice were red‐coloured due to high concentrations of the recently described Pyramimonas tychotreta Daugbjerg. Light microscopy of living material revealed that the population was comprised of quadriflagellate motile cells and thick‐walled cysts. The red colour was due to large numbers of secondary carotenoid‐containing granules, positioned in the periphery of motile cells and cysts. Mature cysts also contained numerous starch grains and lipid droplets. Cells from a red‐coloured field sample turned green overnight as the secondary carotenoids disappeared when cells were placed in low light conditions. The sample then exhibited the typical grass‐green colour of motile cells observed in water samples from the area. Under reduced light motile cells showed strong positive phototaxis. The encystment process involved the asexual transformation of quadriflagellate cells into cysts. A single type of square cyst scale, with perforated floors and walls, replaced the body scales of motile cells. A marked extension, often ending in a hook was at each corner of the cyst scales. Germinating cysts produced four motile cells. Electron microscopy showed the cyst wall to be tri‐layered, with a thin, electron‐dense inner layer, a thick middle layer and a thin outer layer. Sea ice samples with dense populations of motile cells and cyst stages also contained elongate uniflagel‐late cells. These cells were covered with box scales, foot‐print scales, an underlayer of pentagonal scales, limuloid scales and flagellar hair scales identical to those present on the quadriflagellate stage. We tentatively suggest that the uniflagellate stage represents a gamete and its presence implies the occurrence of sexual reproduction. Although, fusion of gametes was not observed, a biflagellate cell with a larger volume was seen which may have been a zygote. How this stage fits into of the life history remains to be explained. 相似文献
10.
Grazing by the planktonic phytoflagellate, Pyramimonas gelidicola McFadden (Chlorophyta: Prasinophyta), and heterotrophic nanoflagellates (HNAN) in meromictic saline Ace Lake in the Vestfold Hills, eastern Antarctica was investigated in the austral summers of 1997 and 1999. Up to 47% of the P. gelidicola population ingested fluorescently labeled prey (FLP). Ingestion rates varied with depth. In January 1997 and November 1999, maximum P. gelidicola ingestion rates of 6.95 and 0.79 FLP·cell?1·h?1, respectively, were measured at the chemocline (6–8 m) where a deep chl maximum composed of phototrophic nanoflagellates (PNAN DCM), predominantly P. gelidicola, persisted all year. During the summers of 1997 and 1999, the grazing P. gelidicola community removed between 0.4% and approximately 16% of in situ bacterial biomass, equivalent to between 4% and>100% of in situ bacterial production. Because of their higher abundance, the community clearance rates of HNAN in Ace Lake generally exceeded those of P. gelidicola, but HNAN removed approximately only 3%–4% of bacterial biomass, equivalent to between 28% and 32% of bacterial production. Pyramimonas gelidicola growth rates were highest at the PNAN DCM concomitant with the highest ingestion rates. It is estimated that during the summer P. gelidicola can derive up to 30% of their daily carbon requirements from bacterivory at the PNAN DCM. This study confirms mixotrophy as an important strategy by which planktonic organisms can survive in extreme, polar, lacustrine ecosystems. 相似文献