A Virus Infection in the Marine Brown Alga Ectocarpus siliculosus (Phaeophyceae)

Laboratory cultures of Ectocarpus siliculosus originating from New Zealand showed a defect in gametangium formation. Nuclear divisions in gametangium initials are not followed by cell wall formation. In the resulting multinucleate cells nuclear DNA increases dramatically, and nuclear membranes disintegrate. Eventually, the entire structure is filled with hexagonal particles of approximately 130 nm diameter. These were isolated and shown by EM to consist of a dense core surrounded by a 3-layered shell. They are released into the culture medium when the host cells burst. Ectocarpus gametes from healthy cultures could be infected by these particles. The resulting partheno-sporophytes developed pathological symptoms, suggesting that the particles are viruses. The expression of the defect is temperature dependent. At 10°C all gametangia are abnormal, while between 15 and 20 °C defective and normal gametangia and gametes are formed on the same plant. Partheno-sporophytes developing from such gametes carry the viral particles expressed in deformed unilocular and plurilocular sporangia.     

The role of triploid hybrids in the evolutionary dynamics of mixed-ploidy populations

Theory suggests that the evolution of autotetraploids within diploid populations will be opposed by a minority-cytotype mating disadvantage. The role of triploids in promoting autotetraploid establishment is rarely considered, yet triploids are often found in natural populations and are formed in experimental crosses. Here, I evaluate the effects of triploids on autotetraploid evolution using computer simulations and by synthesizing research on the evolutionary dynamics of mixed-ploidy populations in Chamerion angustifolium (Onagraceae). Simulations show that the fate of a tetraploid in a diploid population varies qualitatively depending on the relative fitness of triploids, the ploidy of their gametes and the fitness of diploids relative to tetraploids. In general, even partially fit triploids can increase the likelihood of diploid–tetraploid coexistence and, in some cases, facilitate tetraploid fixation. Within the diploid–tetraploid contact zone of C. angustifolium , mixed populations are common (43%), and often (39%) contain triploids. Greenhouse and field studies indicate that triploid fitness is low (9% of diploids) but variable. Furthermore, euploid gametes produced by triploids can be x , 2 x or 3 x and contribute the majority (62%) of new polyploids formed in each generation (2.3 × 10⁻³). Although triploid bridge, alone, may not account for the evolution of autotetraploidy in C. angustifolium , it probably contributes to the prevalence of mixed-ploidy populations in this species. Therefore, in contrast to hybrids in homoploid species, triploids may actually facilitate rather than diminish the fixation of tetraploids by enhancing the rate of formation.  © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 537–546.     

中国春phlb突变体与多倍体Aegilops杂种F1回交植株（BC1F1）的细胞学研究

中国春phlb突变体与5个多倍体Aegilops的杂种F1用普通小麦进行回交,并对回交一代（BC1F1）的细胞学进行了研究。结果表明,BC1F1植株花粉母细胞最高染色体数56条,最低35条,一般情况下phlb基因可以增加BC1F1植株的染色体数（不是所有组合）,但不能增加染色体配对水平。杂种F1回交时有效雌配子最高染色体数在含有phlb基因组合中高于不含phlb基因的组合,但最低不杂色体数目相等,且含有21条染色体雌配子最具有竞争力,同时也证明,回交的成功并不取决于杂种F1通过重建分裂（restitution division)形成的未减数雌配子。     

A novel potassium channel encoded by Ectocarpus siliculosus virus

Kcv, the first identified viral potassium channel encoded by the green algae Paramecium bursaria chlorella virus (PBCV-1), conducted K(+) selective currents when expressed in heterologous systems. This K(+) channel was proposed to be important for PBCV-1 infection and replication. In the present study, we identified and functionally characterized a novel K(+) channel Kesv, encoded by Ectocarpus siliculosus virus that infects filamentous marine brown algae. Kesv encodes a protein of 124 amino acids and is 21.8% identical and 37.1% homologous to Kcv. Membrane topology programs predicted that Kesv consists of three transmembrane domains. When expressed in Xenopus oocytes, Kesv induced largely instantaneous, K(+) selective currents that were sensitive to block by Ba(2+) and amantadine. Thus, Kesv along with Kcv, constitutes an emerging family of viral potassium channels, which may play important roles in the life cycle of viruses.     

Selection of cryoprotectants based on their toxic effects on oyster gametes and embryos

Cryopreservation is a valuable tool for aquaculture by providing continuous seed production, regardless of the spawning seasons. This study aimed to select the least toxic among the cryoprotectants dimethyl sulfoxide (Me2SO), propylene glycol (PG), and methanol (MET) based on their toxicological effects on Crassostrea rhizophorae gametes and trochophores. They were exposed for 10, 20, and 30 min to a range of concentrations of those cryoprotectants. The endpoint was EC15-24 h (effective concentration which causes abnormalities in 15% of the population exposed to the cryoprotectants for 24 h), recently determined as the chronic value (the concentration at which chronic effects are first observed) for C. rhizophorae embryonic phases. There were no significant differences (p>0.05) among the exposure times in Me2SO toxic effects to either gametes or trochophores. For MET, the increase in exposure time resulted in higher toxicity for gametes, but not for trochophores, while for PG there was a significant (p>0.05) increase in toxicity with the increase of exposure for trochophores and spermatozoa, but not for oocytes. For gametes, MET was the most toxic among the cryoprotectants, while PG was the most toxic for trochophores.     

Signalling and sex in the social amoebozoans

The social amoebozoans have a life tricycle consisting of asexual multicellular development leading to fruiting bodies, sexual multicellular development resulting in macrocysts, and unicellular development generating microcysts. This review covers the events of sexual development in the best‐studied heterothallic (Dictyostelium discoideum) and homothallic (D. mucoroides) mating systems. Sexual development begins with pheromonal interactions that produce fusion‐competent cells (gametes) which undergo cell and pronuclear fusion. Calcium‐ and calmodulin‐mediated signalling mediates these early events. As they initiate chemotactic signalling, each zygote increases in size becoming a zygote giant cell. Using cyclic AMP (cAMP), the zygote chemotactically lures in amoebae and engulfs them in an act of cannibalistic phagocytosis. Chemotaxis proceeds more quickly than endocytosis because the breakdown products of cAMP (5‐AMP, adenosine) bind to a presumptive adenosine receptor to inhibit sexual phagocytosis. This slowing of phagocytosis allows amoebae to accumulate around the zygote to form a precyst aggregate. Zygote giant cells also produce several other signalling molecules that feed back to regulate early events. The amoebae surrounding the zygote seal their fate as zygotic foodstuff by secreting a primary cellulose wall, the extracellular sheath, around the zygote and aggregated amoebae, which prevents their escape. Phagocytosis within this precyst continues until all peripheral amoebae are internalized as endocytes and the final macrocyst wall is formed. Endocyte digestion results in a mature macrocyst with a uniform cytoplasm containing a diploid nucleus. After detailing the morphological events of heterothallic and homothallic mating, we review the various intercellular signalling events and other mechanisms involved in each stage. This complete and comprehensive review sets the stage for future research on the unique events that characterize sex in the social amoebozoans.     

Female gametogenesis and female gamete germination in the anisogamous green alga Codium fragile subsp. novae‐zelandiae (Bryopsidophyceae,Chlorophyta)

Female gametogenesis was studied in the dioecious siphonous green alga Codium fragile subsp. novae‐zelandiae (J. Agardh) P. C. Silva using light and electron microscopy. Early during gametogenesis the protoplasm was uniform; then it separated in portions, while fusiform chloroplasts and nuclei increased in numbers. Some features of the nuclear divisions were similar to those of other Bryopsidophyceae. They were acentric and semi‐open. Pairs of parallel electron‐dense lines resembling synaptonemic complexes were observed in several prophase nuclei indicating meioses. In metaphase the nuclear envelope showed polar fenestrae from which the spindle emerged. No spindle microtubule nucleating material was visible and chromosome kinetochores were evident. Mature female gametes were pyriform with a hyaline anterior end from which the two flagella emerged. Mature gametes had a spherical nucleus surrounded by a mitochondrion and numerous discoid chloroplasts. Female gametes germinated parthenogenetically in culture and also inside gametangia, involving loss of flagella, rounding and lengthening of cells, multiplication of chloroplasts with well developed thylakoid systems, vacuolization and synthesis of a fibrillar cell wall.     

Meiotic restriction in emmer wheat is controlled by one or more nuclear genes that continue to function in derived lines

Highly fertile F₁ hybrids were made between Triticum turgidum L. ssp. turgidum (2n = 28, AABB) and Aegilops tauschii Coss. (2n = 14, DD) without embryo rescue and hormone treatment. The F₁ plants had an average seed set of 25%. Approximately 96% of the F₂ seeds were able to germinate normally and about 67% of the F₂ plants were spontaneous amphidiploid (2n = 42, AABBDD). Cytological analysis of male gametogenesis of the F₁ plants showed that meiotic restitution is responsible for the high fertility. A mitosis-like meiosis led to meiotic restitution at either of the two meiotic divisions resulting in unreduced gametes. Test crosses of the T. t. turgidum–Ae. tauschii amphidiploid with Ae. variabilis and rye suggested that the mitosis-like meiosis is controlled by one or more nuclear genes that continue to function in derived lines. This discovery indicates a potential application of such genes in producing double haploids.     

Determination of n-l-1 Gamete Transmission Rate of Trisomics and Location of Gene Controlling 2n Gamete Formation in Chinese Cabbage （Brassica rapa）

A set of trisomics of Chinese cabbage was used for determining the n-I-1 gamete transmission rate and locating the gene controlling 2n gamete formation on the corresponding chromosome. The results showed that the transmission rates of extra chromosomes in different trisomics varied from 0% to 15.38% by male gametes and from 0% to 17.39% by female gametes. Of the nine F2 populations derived from the hybridizations between each trisomic and Bp058 （2n gamete material）, only Tri- 4xBp058 showed that the segregation ratio of plants without 2n gamete formation to plants with 2n gamete formation was 10.38：1, which fitted the expected segregation ratio of the trisomics （AAa） based on the 7.37% of n＋l gamete transmission through female and 5.88% through male. In other populations the segregation ratios varied from 2.48：1 to 3.72：1, which fitted the expected 3：1 segregation ratio of the bisomics （Aa）. These results suggested that the gene controlling 2n gamete formation in Chinese cabbage Bp058 was located on chromosome 4. Further trisomic analysis based on the chromosome segregation and the incomplete stochastic chromatid segregation indicated that the gene locus was tightly linked to the centromere.