Sexual Fusion Research Articles

Sporochnus keyari sp. nov. (Sporochnales, Phaeophyceae) from Japan

ABSTRACT In the genus Sporochnus (Sporochnales, Phaeophyceae), Okamura reported S. radiciformis and S. scoparius in Japan in 1922; however, S. scoparius was later synonymized with S. radiciformis, as Okamura’s S. radiciformis was considered to be a young stage of S. scoparius. Therefore, only one species, S. radiciformis, has been recognized in Japan, until the reported occurrence of a second species, S. dotyi, and suggestion that the species identified as S. radiciformis in Japan was genetically distinct from true S. radiciformis described from Australia. We now report findings that based on molecular phylogeny (atpB, rbcL, atp6, cox3) and morpho-anatomical analyses confirming that the common Japanese Sporochnus species is distinct from true S. radiciformis, and we therefore describe a new species, S. keyari sp. nov. This new species differs from S. radiciformis in having less-branched erect thalli, longer terminal assimilatory filaments (trichothallic hairs), and larger unilocular zooidangia, and from S. bolleanus in having more robust thallus axes. In gross morphology, S. keyari is distinguished from S. dotyi, which is also distributed in Japan, in having more slender thalli and lacking greenish structural colour of the assimilatory filaments. In culture, unizoids (zoospores) released from unilocular zooidangia developed into monoicous gametophytes forming antheridia and oogonia at the distal ends of the filaments. Actual sexual fusion was not observed, but presumably fertilization occurred within oogonia and new sporophytes developed in situ within oogonia. Sporophytes were at first uniseriate, but later formed terete thalli by trichothallic growth, with terminal assimilatory filaments.

Plasma Membrane Fusion Is Specifically Impacted by the Molecular Structure of Membrane Sterols During Vegetative Development of Neurospora crassa.

Cell-to-cell fusion is crucial for the development and propagation of most eukaryotic organisms. Despite this importance, the molecular mechanisms mediating this process are only poorly understood in biological systems. In particular, the step of plasma membrane merger and the contributing proteins and physicochemical factors remain mostly unknown. Earlier studies provided the first evidence of a role of membrane sterols in cell-to-cell fusion. By characterizing different ergosterol biosynthesis mutants of the fungus Neurospora crassa, which accumulate different ergosterol precursors, we show that the structure of the sterol ring system specifically affects plasma membrane merger during the fusion of vegetative spore germlings. Genetic analyses pinpoint this defect to an event prior to engagement of the fusion machinery. Strikingly, this effect is not observed during sexual fusion, suggesting that the specific sterol precursors do not generally block membrane merger, but rather impair subcellular processes exclusively mediating fusion of vegetative cells. At a colony-wide level, the altered structure of the sterol ring system affects a subset of differentiation processes, including vegetative sporulation and steps before and after fertilization during sexual propagation. Together, these observations corroborate the notion that the accumulation of particular sterol precursors has very specific effects on defined cellular processes rather than nonspecifically disturbing membrane functioning. Given the phenotypic similarities of the ergosterol biosynthesis mutants of N. crassa during vegetative fusion and of Saccharomyces cerevisiae cells undergoing mating, our data support the idea that yeast mating is evolutionarily and mechanistically more closely related to vegetative than sexual fusion of filamentous fungi.

The molecular foundations of zygosis.

Zygosis is the generation of new biological individuals by the sexual fusion of gamete cells. Our current understanding of eukaryotic phylogeny indicates that sex is ancestral to all extant eukaryotes. Although sexual development is extremely diverse, common molecular elements have been retained. HAP2-GCS1, a protein that promotes the fusion of gamete cell membranes that is related in structure to certain viral fusogens, is conserved in many eukaryotic lineages, even though gametes vary considerably in form and behaviour between species. Similarly, although zygotes have dramatically different forms and fates in different organisms, diverse eukaryotes share a common developmental programme in which homeodomain-containing transcription factors play a central role. These common mechanistic elements suggest possible common evolutionary histories that, if correct, would have profound implications for our understanding of eukaryogenesis.

Apocarotenoids produced from β-carotene by dioxygenases from Mucor circinelloides.

Mucor circinelloides exhibits the complex sexual behaviour that is induced in other Mucoromycotina by a family of apocarotenoids called trisporoids. The genome of M. circinelloides contains four genes encoding putative carotenoid cleavage dioxygenases. The gene products of two of them were sufficient to convert β-carotene into the precursors of three families of apocarotenoids, both in vitro and in the Escherichia coli heterologous in vivo system. The first of these products, CarS, cleaved the C40 β-carotene into the C15 precursor of cyclofarnesoids and a C25 apocarotenal that was converted by the second enzyme, AcaA, into the C18 precursor of trisporoids and the C7 precursor of methylhexanoids. Apocarotenoids were not found in single or mixed cultures of the two strains of opposite sex, whose interaction readily produced zygospores, the sexual fusion cells.

Studies on woloszynskioid dinoflagellates VIII: life cycle, resting cyst morphology and phylogeny of Tovellia rinoi sp. nov. (Dinophyceae)

:Tovellia rinoi nov. sp. is described on the basis of light microscopic and scanning electron microscopic examination of motile cells and resting cysts and the phylogenetic analysis of partial sequences of the large subunit ribosomal rRNA gene. The species was isolated from a flooded area near Aveiro, Portugal, and followed in culture through all stages of the life cycle, including formation of vegetative cells and gametes, sexual fusion, planozygote division through division cysts and the production of resting cysts. Motile cells had an ovate-conical epicone and a truncated or slightly excavated hypocone and were a little flattened dorsoventrally. Cell length was mostly 9–19 μm, the smaller cells less pigmented and with the potential to act as gametes but also capable of vegetative multiplication. The amphiesma had three series of vesicles on the epicone, one in the cingulum and two on the hypocone and an apical line of plates (ALP) oriented almost dorsoventrally across the cell apex. One vesicle separated the ALP from the cingulum on the ventral side, two on the dorsal side. The resting cysts, showing an equatorial constriction and densely covered by hair-like spines, represented a new type within the family Tovelliaceae. The new species formed a well-supported sister group to the other Tovellia species in a LSU rDNA–derived phylogeny. Sexual fusion started with gametic contact within ‘dancing groups’ of small cells. The initial contact on the mid-ventral side of both gametes was often visible as a hyaline bridge, which apparently involved a globular structure protruding from the ventral ridge of one or both gametes. The two gametes in a fusing pair behaved differently, with one gamete rotating as it fused into its partner until gametic eyespots merged and the gametic longitudinal flagella assumed the position of the paired longitudinal flagella of the planozygote. Resting cysts developed from large cells morphologically identifiable as planozygotes, with cyst spines growing rapidly. Conversion of planozygotes into division cysts that produced motile cells was also observed. Germinating cysts produced regularly two motile cells, each apparently with a single longitudinal flagellum. Nuclear cyclosis was not detected at any stage of the life cycle.

Insights into the loss factors of phytoplankton blooms: The role of cell mortality in the decline of two inshore Alexandrium blooms.

While considerable effort has been devoted to understanding the factors regulating the development of phytoplankton blooms, the mechanisms leading to bloom decline and termination have received less attention. Grazing and sedimentation have been invoked as the main routes for the loss of phytoplankton biomass, and more recently, viral lysis, parasitism and programmed cell death (PCD) have been recognized as additional removal factors. Despite the importance of bloom declines to phytoplankton dynamics, the incidence and significance of various loss factors in regulating phytoplankton populations have not been widely characterized in natural blooms. To understand mechanisms controlling bloom decline, we studied two independent, inshore blooms of Alexandrium fundyense, paying special attention to cell mortality as a loss pathway. We observed increases in the number of dead cells with PCD features after the peak of both blooms, demonstrating a role for cell mortality in their terminations. In both blooms, sexual cyst formation appears to have been the dominant process leading to bloom termination, as both blooms were dominated by small-sized gamete cells near their peaks. Cell death and parasitism became more significant as sources of cell loss several days after the onset of bloom decline. Our findings show two distinct phases of bloom decline, characterized by sexual fusion as the initial dominant cell removal processes followed by elimination of remaining cells by cell death and parasitism.

Taxonomic reinvestigation of Petalonia (Phaeophyceae, Ectocarpales) in southeast of Honshu, Japan, with a description of Petalonia tenuis sp. nov.

:We conducted a phylogenetic and morphological reinvestigation of Petalonia species from the Pacific coast southeast of Honshu, Japan. Phylogenetic analyses based on plastid rbcL and the nuclear ITS regions resulted in three genetically distinct species: P. binghamiae, P. fascia, and Petalonia sp. Petalonia sp. was characterized by the medullary structure showing intermediate characteristics between those of P. binghamiae and P. fascia as well as by the thinner thallus. In addition, the habitat and the seasonality of Petalonia sp. were slightly different from those of the two species. Sexual fusion of plurizoids was observed on Petalonia sp., and the morphology of the prostrate sporophytes agreed with the previous reports of P. binghamiae and P. fascia. According to the characteristics, Petalonia sp. is described as a new species, P. tenuis sp. nov.

A Quantitative Assessment of the Role of the Parasite Amoebophrya in the Termination of Alexandrium fundyense Blooms within a Small Coastal Embayment

Parasitic dinoflagellates of the genus Amoebophrya infect free-living dinoflagellates, some of which can cause harmful algal blooms (HABs). High prevalence of Amoebophrya spp. has been linked to the decline of some HABs in marine systems. The objective of this study was to evaluate the impact of Amoebophrya spp. on the dynamics of dinoflagellate blooms in Salt Pond (MA, USA), particularly the harmful species Alexandrium fundyense. The abundance of Amoebophrya life stages was estimated 3–7 days per week through the full duration of an annual A. fundyense bloom using fluorescence in situ hybridization coupled with tyramide signal amplification (FISH- TSA). More than 20 potential hosts were recorded including Dinophysis spp., Protoperidinium spp. and Gonyaulax spp., but the only dinoflagellate cells infected by Amoebophrya spp. during the sampling period were A. fundyense. Maximum A. fundyense concentration co-occurred with an increase of infected hosts, followed by a massive release of Amoebophrya dinospores in the water column. On average, Amoebophrya spp. infected and killed ∼30% of the A. fundyense population per day in the end phase of the bloom. The decline of the host A. fundyense population coincided with a dramatic life-cycle transition from vegetative division to sexual fusion. This transition occurred after maximum infected host concentrations and before peak infection percentages were observed, suggesting that most A. fundyense escaped parasite infection through sexual fusion. The results of this work highlight the importance of high frequency sampling of both parasite and host populations to accurately assess the impact of parasites on natural plankton assemblages.

Blowin' in the wind… 100 Ma old multi-staged dinoflagellate with sexual fusion trapped in amber: Marine–freshwater transition

Here we report the unexpected discovery of multi-staged dinoflagellates with organic cellular contents from a paralic habitat trapped in 100millionyear (100Ma) old amber. Amber formed from resin, a fluid medium, that trapped, then remarkably embedded and preserved soft parts of organisms usually destroyed by fossilization processes. We assume that the marine-costal dinoflagellates reached the sticky resin carried away by the wind, inside spray droplets. We answer to a fundamental question dealing with the Peridiniaceae: the paratabulation of Cretaceous cysts reflects the tabulation of Cretaceous thecae. We provide the first life cycle of the fossil record with evidence of cellulosic thecae, sexual fusion and zygote. We highlight an ancestral behaviour for the sexual phase: naked gametes complete fusion outside of gametic thecae, a process known in rare extant Peridinium species. The new taxon, Succiniperidinium inopinatum gen. et sp. nov., belongs to the Peridiniaceae and shares characters with extant marine-brackish Scrippsiella and two freshwater Peridinium clades identified by morphological characters (tabulation, cingular plates, ecdysis, plasmogamy) and molecular phylogenies. Understanding the processes of marine–freshwater transition in microbial lineages is a central goal in evolutionary ecology. Marine dinoflagellates passed through the osmotic barrier and the studies of marine-costal Cretaceous species help to understand the adaptation and the diversification of these species. We discuss the migration according to biological, paleontological and molecular phylogenies data and suggest that the freshwater colonization was the result of Cretaceous species adapted to costal habitats; their lineage isolated in ponds following the Cenozoic global sea-level fall passed through the osmotic barrier. A Scrippsiella-like group (i.e. Subtilisphaera terrula, Palaeoperidinium cretaceum and Succiniperidinium inopinatum gen. et sp. nov.) is suggested as intermediate species in the Peridinium freshwater colonization line.

Complexities of bloom dynamics in the toxic dinoflagellate Alexandrium fundyense revealed through DNA measurements by imaging flow cytometry coupled with species-specific rRNA probes

Measurements of the DNA content of different protist populations can shed light on a variety of processes, including cell division, sex, prey ingestion, and parasite invasion. Here, we modified an Imaging FlowCytobot (IFCB), a custom-built flow cytometer that records images of microplankton, to measure the DNA content of large dinoflagellates and other high-DNA content species. The IFCB was also configured to measure fluorescence from Cy3-labeled rRNA probes, aiding the identification of Alexandrium fundyense (syn. A. tamarense Group I), a photosynthetic dinoflagellate that causes paralytic shellfish poisoning (PSP). The modified IFCB was used to analyze samples from the development, peak and termination phases of an inshore A. fundyense bloom (Salt Pond, Eastham, MA, USA), and from a rare A. fundyense ‘red tide’ that occurred in the western Gulf of Maine, offshore of Portsmouth, NH (USA). Diploid or G2 phase (‘2C’) A. fundyense cells were frequently enriched at the near-surface, suggesting an important role for aggregation at the air-sea interface during sexual events. Also, our analysis showed that large proportions of A. fundyense cells in both the Salt Pond and red tide blooms were planozygotes during bloom decline, highlighting the importance of sexual fusion to bloom termination. At Salt Pond, bloom decline also coincided with a dramatic rise in infections by the parasite genus Amoebophrya. The samples that were most heavily infected contained many large cells with higher DNA-associated fluorescence than 2C vegetative cells, but these cells' nuclei were also frequently consumed by Amoebophrya trophonts. Neither large cell size nor increased DNA-associated fluorescence could be replicated by infecting an A. fundyense culture of vegetative cells. Therefore, we attribute these characteristics of the large Salt Pond cells to planozygote maturation rather than Amoebophrya infection, though an interaction between infection and planozygote maturation may also have contributed. The modified IFCB is a valuable tool for exploring the conditions that promote sexual transitions by dinoflagellate blooms but care is needed when interpreting results from samples in which parasitism is prevalent.

Evolutionary rescue of a green alga kept in the dark

Chlamydomonas (Chlorophyta) can grow as a heterotroph on medium supplemented with acetate in the dark. A long-term experiment to investigate adaptation to dark conditions was set up with hundreds of replicate lines. Growth was initially slow, and most lines became extinct when transferred every few weeks. Some lines survived through the expansion of lineages derived from cells with extreme phenotypes and exhibited a U-shaped curve of collapse and recovery. Two short-term experiments were set up to evaluate the effect of sex on the frequency of 'evolutionary rescue' by deriving replicate lines from ancestral populations with contrasting sexual histories that had been cultured in the light for hundreds of generations. When transferred to dark conditions of growth, lines derived from obligately sexual populations survived more often than lines derived from facultatively sexual or asexual populations. This reflected the higher initial frequency of cells able to grow in the dark, due to greater genetic diversity supported by sexual fusion and recombination. The greater probability of evolutionary rescue suggests a general reason for the prevalence of sexual species.

The risks of hospitality

Cellular integrity is essential, because the chemical gradients necessary to sustain life would otherwise be subdued by entropy. No wonder that, already, the earliest life-forms have developed mechanisms to defend their integrity against invaders. However, there are two occasions where cells have to adopt a softer approach towards integrity: first, when a cell has to take up molecules or other cells to support its own metabolism (endocytosis in its variants); second, when two cells of the same species fuse to initiate sexual propagation. Whereas the uptake of food is perfectly compatible with defence, the defence machinery has to be quelled or at least modulated during sexual fusion in such a way that the DNA of the (male) “guest” is not damaged. This evolutionary reasoning already illustrates that any fusion or perforation at the outer membrane must be under the control of specific signals. Many pathogens have developed, during an evolutionary arms race with their hosts, means to manipulate this signalling to circumvent or suppress defence by so called effectors (Jones and Dangl 2006), which allows them to remodel the plasma membrane and to penetrate into the host cell without killing it. It is rather unlikely that these so called biotrophic pathogens have invented such a complex manipulation de novo—they probably just usurped a signal cascade that already functioned in the host cell in a different context: to downregulate defence during sexual fusion. Two contributions in the current issue provide surprising details of haustoria formation that link sexuality with defence. The work by Guan et al. (2011) in the current issue investigates resistance of the Chinese wild Vitis pseudoreticulata against powdery mildew (Uncinula necator). This biotrophic fungus penetrates into the epidermal cell and forms a haustorium which allows the invader to profit from the metabolism of the host. From the comparison of the resistant with a susceptible host genotype, they identified a glyoxal oxidase that is upregulated in the resistant host and localized in the apoplast. The function of this enzyme in plants is unclear; in wood-degrading fungi where it was originally discovered, glyoxal oxidase is secreted and seems to support the degradation process by generating hydroxy peroxides. The induction of glyoxal oxidase in the resistant V. pseudoreticulata might thus be either adaptive in nature or just a byproduct of defence. To test this, Guan et al. (2011) overexpressed the glyoxal oxidase in the susceptible host by agroinfiltration into young leaves that were subsequently infected with powdery mildew. They observed delayed and even partially arrested colonization in those leaf areas, where the transgene was expressed. Thus, the induction of glyoxal oxidase is sufficient to confer resistance to powdery mildew probably through the generation of extracellular reactive oxygen species that seem to suppress haustoria formation. The work by Hiratsuka and Terasaka (2011) in the current issue describes haustoria formation in a completely different context. The pollen tubes of many gymnosperms (that represent an evolutionary precursor of “modern” angiosperm pollen tubes) are branched. Some of these branches do not convey sperms, but penetrate into the extracellular matrix of the female nucellus acting as haustoria that support the male gametophyte during the often several months between pollination and sperm delivery. The transmitting tissue in the style secretes specific arabinogalactan proteins that guide pollen tube Handling Editor: Peter Nick

Genes encoding a striatin-like protein ( ham-3) and a forkhead associated protein ( ham-4) are required for hyphal fusion in Neurospora crassa

Cell–cell fusion during fertilization and between somatic cells is an integral process in eukaryotic development. In Neurospora crassa, the hyphal anastomosis mutant, ham-2, fails to undergo somatic fusion. In both humans and Saccharomyces cerevisiae, homologs of ham-2 are found in protein complexes that include homologs to a striatin-like protein and a forkhead-associated (FHA) protein. We identified a striatin ( ham-3) gene and a FHA domain ( ham-4) gene in N. crassa; strains containing mutations in ham-3 and ham-4 show severe somatic fusion defects. However, ham-3 and ham-4 mutants undergo mating-cell fusion, indicating functional differences in somatic versus sexual fusion events. The ham-2 and ham-3 mutants are female sterile, while ham-4 mutants are fertile. Homozygous crosses of ham-2, ham-3 and ham-4 mutants show aberrant meiosis and abnormally shaped ascospores. These data indicate that, similar to humans, the HAM proteins may form different signaling complexes that are important during both vegetative and sexual development in N. crassa.

The Occurrence of Laminarionema elsbetiae (Phaeophyceae) on Rhodymenia pseudopalmata (Rhodophyta) from the Patagonian Coasts of Argentina: Characteristics of the Relationship in Natural and Experimental Infections, and Morphology of the Epi-endophyte in Unialgal Free Cultures

The occurrence of Laminarionema elsbetiae (Ectocarpaceae, Phaeophyceae), as epi-endophyte of Rhodymenia pseudopalmata (Rhodymeniales, Rhodophyta), described from Santa Isabel, Rawson, Argentina. L. elsbetiae grows in the host tissues forming epi-endophytic relationship in the epidermal, cortical and medullar layers. Epiphytic thalli of L. elsbetiae were unbranched filaments emerging from hostis surface. Reproductive structures of L. elsbetiae on the host were absent. On the contrary, free cultured individuals formed different reproductive structures. Macrozoosporangia containing a single large motile zoospore originated from vegetative cells, they were conical to cylindrical in shape, 30-50 μm in length and 18-20 μm in wide. Uniseriate plurilocular zoosporangia were cylindrical shape, 40 μm in length and 10-13 μm in wide. Sexual fusion was not seen. In mixed cultures of L. elsbetiae with R. pseudopalmata fronds, L. elsbetiae infected the host, grew as in natural host and, formed macrosporangia between host subcortical cells. Gametophytes of L. elsbetiae were filaments with diffuse growth, branched with a branch pattern alternate or opposite. Gametangia were plurilocular, uni or biseriate and lateral. When mature they contained 2 to 6 isogametes. The presence L. elsbetiae on R. pseudopalmata could be defined as an epi-endophytic relationship. The percentage of infection of R. pseudopalmata thalli by L. elsbetiae was 34%.A25% of the infected thalli presented a low, non-symptomatic level infection, whereas a 62% and a 13% of them exhibited respectively moderate and high indexes of infection.

The “Cheshire Cat” escape strategy of the coccolithophoreEmiliania huxleyiin response to viral infection

The coccolithophore Emiliania huxleyi is one of the most successful eukaryotes in modern oceans. The two phases in its haplodiploid life cycle exhibit radically different phenotypes. The diploid calcified phase forms extensive blooms, which profoundly impact global biogeochemical equilibria. By contrast, the ecological role of the noncalcified haploid phase has been completely overlooked. Giant phycodnaviruses (Emiliania huxleyi viruses, EhVs) have been shown to infect and lyse diploid-phase cells and to be heavily implicated in the regulation of populations and the termination of blooms. Here, we demonstrate that the haploid phase of E. huxleyi is unrecognizable and therefore resistant to EhVs that kill the diploid phase. We further show that exposure of diploid E. huxleyi to EhVs induces transition to the haploid phase. Thus we have clearly demonstrated a drastic difference in viral susceptibility between life cycle stages with different ploidy levels in a unicellular eukaryote. Resistance of the haploid phase of E. huxleyi provides an escape mechanism that involves separation of meiosis from sexual fusion in time, thus ensuring that genes of dominant diploid clones are passed on to the next generation in a virus-free environment. These "Cheshire Cat" ecological dynamics release host evolution from pathogen pressure and thus can be seen as an opposite force to a classic "Red Queen" coevolutionary arms race. In E. huxleyi, this phenomenon can account for the fact that the selective balance is tilted toward the boom-and-bust scenario of optimization of both growth rates of calcifying E. huxleyi cells and infectivity of EhVs.

Comparative study of the life cycles of Alexandrium tamutum and Alexandrium minutum (Gonyaulacales, Dinophyceae) in culture1

The microalgal genus Alexandrium includes species known to produce paralytic shellfish poisoning (PSP). Due to the importance of discriminating between HAB‐forming species, we compared the undescribed life‐cycle pattern of Alexandrium tamutum Montresor, Beran et U. John and of its toxic relative Alexandrium minutum Halim. Sexual stages, asexual and sexual division, mating type, and nuclear morphology were studied in both species. Sexual cysts are known to be morphologically identical. However, the relative size of the U‐shaped nucleus may be used to differentiate between the cysts of these species since DNA packaging in the resting cysts was lower in A. tamutum than in A. minutum, species in which the planozygote nucleus was reduced to half its volume prior to encystment. The dormancy period of the cysts was <20 d for A. tamutum, but longer than 1 month for A. minutum. In both species, cyst appearance needed to be explained by the existence of more than two sexual types (+/–), which indicates a complex heterothallic mating type. However, planozygotes of both species may divide instead of encysting. This characteristic was used for nutritional and heritage studies. Isolated planozygotes of both species encysted in larger percentages in medium deficient in both nitrates and phosphates (L/15) than in medium without phosphates added (L‐P), a medium in which most planozygotes neither divide nor encyst. Parental strains of A. minutum with and without the ventral pore formed planozygotes and, later, offspring with the ventral pore, although apparently smaller than usual. A synchronization–flow cytometry method for discriminating diploids formed by sexual fusion (planozygotes) from cells with 2C DNA content resulting from self‐duplication of DNA (dividing cells) was described. The results indicated that the maximum percentage of A. minutum planozygotes (20%) was achieved only 3 to 5 d after crossing the parental strains, and that light might not be needed for the sexual fusion and formation of planozygotes.

MECHANISM OF GAMETE FUSION IN DINOPHYSIS FORTII (DINOPHYCEAE, DINOPHYTA): LIGHT MICROSCOPIC AND ULTRASTRUCTURAL OBSERVATIONS1

A variety of studies have examined the sexual life cycle of species belonging to the genus Dinophysis Ehrenberg. Here, we used TEM to investigate the mechanism of cellular fusion during the sexual life cycle in Dinophysis fortii Pavillard. We observed that fusion always occurred between a normal‐sized cell and a small cell following attachment of their ventral margins. After cell attachment, the small cell moved toward the epitheca of the normal‐sized cell, and the cingular and sulcal lists of the small cell shrunk or were almost lost. The epitheca of the normal‐sized cell then opened between the cingulum plates and the upper cingular list, after which the small cell was gradually engulfed. This is the first ultrastructural observation in a dinoflagellate of a larger cell opening its epitheca to engulf the smaller gamete. In another case, the normal‐sized cell did not open the epitheca, the cell wall of the attached small cell underwent extensive extracellular digestion, and the cytoplasm appeared to flow into the normal‐sized cell via the periflagellar area. Inflow of the nucleus was not observed in this case, suggesting that it represented a failure of sexual fusion. In both cases, membranous separations between the cytoplasm of the two cells were not observed. At the beginning of the fusion process, the nucleus of the small cell was substantially deformed. The planozygote, formed upon completion of sexual fusion, sometimes had two longitudinal flagella, but was identical to a normal vegetative cell in its cellular shape, as already mentioned by previous authors.

Theoretical Inquiry: Language, Linguistics, and Literature by Austin E. Quigley

MLR, 101 .2, 2006 53I projected adult subject is imagined as having 'no relation to dependency, no relation to themother' (p. 86). Perhaps the most striking aspect of this essay is its emotive tone. Johnson writes of Sylvia Plath's failed attempts to tell her mother that she 'hated' her and of the 'inexpressible hurt' inflicted on her mother; she writes too of mothers 'shouldering the blame' forwhat has 'malfunctioned' in the relationship with the child. What is at stake seems tomatter (in both senses, as significance and asmateriality) more than or differently from-the ideals of aesthetic wholeness or of sexual fusion. Discussing the violence directed to and felt by mothers, Johnson notes that the construction of ideal motherhood conflicts with aworld inwhich maternal child abuse is 'very real'. Johnson's subtle readings, too, are here 'very real', powerfully engaging with affects and effects which exceed (even as they are produced by) rhetorical strategies. LOUGHBOROUGH UNIVERSITY CLAREHANSON Theoretical Inquiry: Language, Linguistics, and Literature. By AUSTIN E. QUIGLEY. New Haven and London: Yale University Press. 2004. xxii+262 pp. /35. ISBN 0-300-IOI66-X. Austin Quigley's writing stresses order and balance, as in this sentence: 'The recur ring appeal of the pluralist perspective is that it recognizes and seeks to address the dangers to critical practice of unreflective monism while seeking also to avoid the alter native danger of uncontrolled relativism but the recurring challenge is to characterize the nature of a compelling and controllable alternative' (p. 20). Each substantive, and each qualifier here, reappears many times in the book, and while perhaps itsAugustan balance, opposing 'multiplicity' to relativism, is an asset for Quigley's position as a Dean at Columbia, it is certainly at the heart of his thesis, which challenges critical theory for its tendencies towards monism-reflective or unreflective-and which asks that different theories listen to each other. After an anonymously titled 'Preface' and 'Introduction', which seem to duplicate each other, he embarks on the theorists he wishes to examine: Saussure, J.R. Firth, Bakhtin, Chomsky, Halliday, andWittgen stein. These, of course, are not the theorists that critical theory leans on (with the exception of Saussure, at the heart of structural linguistics, and Bakhtin), but they are the subjects of amost scrupulous and interesting analysis, examining their rela tionships to language, and to the creation of systems of thought within linguistics, and finding each, with the exception of Wittgenstein, about whom Quigley writes excellently, imprisoned in their own system, just at the moment of their maximum achievement. The theory each of them creates cannot quite be self-sufficient, and the conclusions on page I23, that Saussure, Chomsky, and Halliday become imprisoned within abstractions which they have done their best to avoid, are very finely made. Three points and criticisms arise, none the less. The model that Quigley uses being that of language, it condemns him to a certain ahistoricism inhis use of theory, aswhen he argues, in a passage typically full of binary opposites, that 'the modern conflict between structuralism and post-structuralism is [. . .] the most recent version of ancient conflicts between authority and anarchy, necessity and freedom, monism and relativism, conviction and contingency, and belief and doubt' (p. 7 ).More critically, itmeans that he is limited to reading theory in relation to linguistics, which cuts down on what he can say about Derrida, who has an address to linguistics, but to more than that. The limited response to deconstruction shows in a refusal to quote Derrida save in the footnotes, and perhaps in too much reliance on John Ellis's Against Deconstruction (Princeton: Princeton University Press, I989). Claiming that deconstruction sees the text as 'internally multiple' (p. I6I), which, of course, comes 532 Reviews near to what he wants to argue for, save that he does not care for deconstruction, he argues that everything in Derrida is inWittgenstein. But this means not seeing what was distinctive about the 'turn to theory' of the I970s: its anti-humanism, and emphasis on the constructed nature of what counts as the 'human'. Taking Saussure's semiology, he ignores Peirce's non-linguistically based semiotics, and so has nothing to say on Deleuze, who takes Peirce as...

Endophytic unicellular chlorophytes: a review of Chlorochytrium and Scotinosphaera

D.E. Wujek and R.H. Thompson. 2005. Endophytic unicellular chlorophytes: a review of Chlorochytrium and Scotinosphaera. Phycologia 44: 254–260.The genera Nautococcopsis and Ectogeron are reduced to synonymy with Chlorochytrium. The inclusion of Scotinosphaera and Kentrosphaera within the genus Chlorochytrium is considered now untenable. Scotinosphaera and Kentrosphaera are considered synonymous, with the name Scotinosphaera having priority. Redefinitions are given for Chlorochytrium and Scotinosphaera based on seven opposed attributes. Chlorochytrium, in germination of the zoospore, secretes an attachment disc; has fundamentally a parietal chloroplast that develops many radiate lobes, few to many pyrenoids; and the vegetative cell contains few to many minute contractile vacuoles. Its first two to four divisions are vegetative. Further division of each protoplast results in biflagellate zoospores that are walled, compressed and have a flagellar papilla. Scotinosphaera lacks an attaching disc; is strictly unicellular with no vegetative divisions; contains an axile chloroplast with many radiate arms; has characteristically one large central pyrenoid; lacks contractile vacuoles; and division results in numerous biflagellate, terete, spindle-shaped zoospores. Old cells may develop one or more localised lamellated, wart-like thickenings of the wall, externally or internally. Sexual fusion has been observed for Chlorochytrium but not for Scotinosphaera. The relationships of Chlorokoryne, Eremotyle, Nautococcus and Excentrosphaera are reviewed.

Solanum commersonii cytoplasm does not improve freezing tolerance in substitution backcross hybrids with frost-sensitive potato species

Solanum commersonii Dun. (cmm) is the most frost hardy wild potato species known, being able to tolerate an acute freezing episode to about -5 C and further acclimate to tolerate −10 C after being exposed to chilling temperatures for several days. Breeding with this species to incorporate its frost-hardiness traits can be accomplished by standard sexual hybridization or protoplast fusion. These methods can result in hybrids that vary in contribution of the cmm plastome. To test the effect of cmm cytoplasm, cytoplasmic substitution backcross hybrids were made with three very frost-sensitive species,S. brachistotrichum, S. cardiophyllum, andS. pinnatisectum, by usingS. commersonii as the female to make an F1, then performing repeated backcross (BC) using the sensitive species as males. Relative freezing tolerance (RFT) of all genotypes was assessed by measurement of ion leakage of excised terminal leaflets subjected to a controlled ice nucleation and simulated freeze-thaw stress. Even against the background of these very sensitive species’ genomes, the cmm cytoplasm of substitution hybrids promoted insignificant improvement in frost hardiness or ability to acclimate. We conclude that either (1) cmm cytoplasm does not contribute to frost hardiness, or (2) if cmm cytoplasmic frost hardiness genes do exist, they must be epistatic to (depend on the presence of) nuclear hardiness genes for expression.