Stages Of Sexual Reproduction Research Articles

A Gene Essential for De Novo Methylation and Development in Ascobolus Reveals a Novel Type of Eukaryotic DNA Methyltransferase Structure

Molecular mechanisms determining methylation patterns in eukaryotic genomes still remain unresolved. We have characterized, in Ascobolus, a gene for de novo methylation. This novel eukaryotic gene, masc1, encodes a protein that has all motifs of the catalytic domain of eukaryotic C5-DNA-methyltransferases but is unique in that it lacks a regulatory N-terminal domain. The disruption of masc1 has no effect on viability or methylation maintenance but prevents the de novo methylation of DNA repeats, which takes place after fertilization, through the methylation induced premeiotically (MIP) process. Crosses between parents harboring the masc1 disruption are arrested at an early stage of sexual reproduction, indicating that the activity of Masc1, the product of the gene, is crucial in this developmental process.

Sexual versus asexual reproduction in an oviparous rope-form sponge, Aplysina cauliformis (Porifera; Verongida)

Summary The order Verongida, considered to be exclusively oviparous and dioecious, exhibits great range in body form, including thin-bodied, rope- and stick-form members which have been postulated to be morphologically adapted to exploit fragmentation as an important asexual reproductive process. Here we report results of a one-year survey of sexual reproductive stages in a rope-form verongid, Aplysina cauliformis, which test the hypotheses of verongiid sexual pattern and reduced resource allocation to sexual reproduction in rope-form sponges. Results confurn the verongiid pattern of oviparity, dioeciousness and production of small oocytes. Data also support the hypothesis that rope-form sponges are characterized by reduced investment in gamete production relative to sponges of other body forms. The sexual reproductive pattern of the main macrosymbiont (parasite) polychaete, Haplosyllis spongicola, shows no correlation to that of its sponge host.

Hexavalent Chromium Induces Gametogenesis in the Freshwater Alga Scenedesmus acutus

The aggregates formed by Scenedesmus acutus cultivated in the presence of 1 mg/liter Cr(VI) persist even after 7 days of treatment. They were examined by fluorescence and electron microscopy and were found to be an early stage of sexual reproduction. They consist of four small cells deprived of a true cell wall and enclosed in a common envelope. When the envelope breaks up they are released in the culture medium as biflagellated mobile cells. These cells have been identified as gametes.

Co-suppression of nitrate reductase host genes and transgenes in transgenic tobacco plants.

Constructs carrying the entire or part of the tobacco nitrate reductase cDNA (NIA) cloned between the promoter and terminator sequences of the 35S RNA of the cauliflower mosaic virus were introduced into tobacco, in an attempt to improve nitrate assimilation. Several transgenic plants that had elevated NIA mRNA and nitrate reductase (NR) activity were obtained. In addition, a few plants that exhibited a chlorotic phenotype characteristic of NR-deficient mutants were also obtained. One of these plants contained no NIA mRNA, no NR activity and accumulated nitrate. This phenotype was therefore assumed to result from co-suppression of 35S-NIA transgenes and host NIA genes. NR-deficient plants were also found among the progeny of transformants overexpressing NIA mRNA. Genetic analyses indicated that these NR-deficient plants were homozygous for the 35S-NIA transgene, although not all homozygous plants were deficient for NR. The ratio of normal to NR-deficient plants in the progeny of homozygous plants remained constant at each generation, irrespective of the state of expression of the NIA genes (active or inactive) in the previous generation. This ratio also remained unchanged when field trials were performed in two areas of France: Versailles and Bergerac. The analysis of homozygous plants revealed that co-suppression was reversible at some stage of sexual reproduction. Indeed, host genes and transgenes reactivated at each generation, and co-suppression always appeared after a lag period of normal growth, suggesting that the phenomenon is developmentally regulated.(ABSTRACT TRUNCATED AT 250 WORDS)

Application of Monoclonal Antibodies to Field samples of Alexandrium species.

Eight monoclonal antibodies reactive against cultured cell surface antigens of genus Alexandrium (Dinophyceae) were tested for cross-reaction with natural field samples from Japanese coastal waters, by the indirect immunofluorescence (IIF) method.In advance of applying monoclonal antibodies to field samples, the reactivity of typical antibodies to cultured cells at various growth stages in asexual and sexual cycles were examined by dot immunoassay and IIF, respectively. As a result, the reactive intensities were constant during the exponential growth phase and decreased a little during the stationary phase. At a different stage of sexual reproduction, these antibodies reacted with the vegetative cells of parent and F1 progenies, but not with the planozygotes and cysts. The reactive spectra of these antibodies to the cells of natural field samples collected from Tanabe Bay (Wakayama Pref.) in May 1990 and 1991, from Ofunato Bay (Iwate Pref.) in June 1991, and from Tachibana Bay (Nagasaki Pref.) in July 1991 almost coincided with those of these antibodies to cultured cells of A. catenella, A. tamarense, and A. affine, respectively. The results of immunological analysis corresponded with those of the morphological features.These monoclonal antibodies appear to be useful for the identification of these organisms from natural sea water.

Benthic Algal Community Dynamics in a Stream during and after a Spate

Changes in a benthic algal community were observed during and after a major storm. Algal abundance, mostly diatoms, increased slightly during a 3-d interval that included the storm on day 1. Positive effects of the storm on benthic algae were indicated by decreases in the proportions of diatoms that were dead, but not in the dead cell numbers, and by decreases in the proportions of sexually reproducing cells. Increases in current or nutrient supply to periphyton during the storm may have stimulated growth of live cells and retarded sexual reproduction. During two 3-d growth periods after the storm, benthic diatoms grew rapidly from 1.1× 10⁷ cells/cm² and seemed to reach a carrying capacity near 5.2× 10⁷ cells/cm² in only 8 days. Density-dependent decreases in growth rates were accompanied by increases in the proportion of diatoms that were dead or in stages of sexual reproduction, indicating nutrient limitation. Immigration was not an important mechanism of accumulation immediately after the storm. However, immigration/colonization rates increased during community development and indicated substantial turnover by cell transport during late succession. Benthic diatom communities are well adapted to storms in temperate climates in streams with gravelbed channel morphology. I hypothesize that benthic diatoms are actually affected positively by most storms and are negatively affected only by the most severe storms that overturn substrates in the stream.

Sexual reproduction and larval morphology of the primitive anthozoan Gonactinia prolifera M. Sars

The sexual reproductive pattern and larval morphology of the primitive anthozoan Gonactinia prolifera M. Sars is described. The species is dioecious and the sex can be determined only by histological examination. Asexual reproduction is by transverse fission and not related to stage of sexual reproduction. Gametes develop in the gastrodermis and later the mesogloea. Fertilization and development is internal and a ciliated planula ≈100μm long and equipped with an apical tuft is released through the pharynx. Development of the larva is larviparous-pelagic-lecithotrophic which is exceptional among sea anemones. Mature eggs occurred from June through January but most frequently from July through November and spermatozoans were found from June through November. Larvae were found only in 1 of 3 yr surveyed and only in November. Structurally, the Gonactinia larva is made of a single blastoderm cell layer surrounded by a fibrous coat of 5 μm. No mesogloea is observed. Each cell has a single cilium surrounded by a circlet of microvilli embedded in the fibrous coat. The blastoderm consists of only secretory cells and blastoderm cells. The implication of the reproductive pattern and the simple morphology of the Gonactinia larva is discussed in relation to anthozoan reproduction.

The species concept in diatoms: Evidence for morphologically distinct, sympatric gamodemes in four epipelic species

Reproductive isolation is demonstrated between morphologically distinct, sympatric demes of four epipelic diatom species inhabiting a small pond. The six demes ofSellaphora pupula, four of them allogamous, one probably autogamous, and one apparently asexual, differ morphologically with respect to size, shape, stria density and pattern. In the pond,Caloneis silicula, Cymatopleura solea, andNeidium ampliatum each contain two allogamous demes, differing principally in size. There are intrinsic barriers to hybridization between the demes, which operate at the earliest stages of sexual reproduction. Such gamodemes are perhaps best treated taxonomically as separate species.

Emericella nidulansin a maxillary sinus fungal mass

Sexual reproductive stages of fungi are very rarely found within mammalian tissues. We report here coexistence of cleistothecia associated with Emericella nidulans and its conidial state, Aspergillus nidulans, in a fungal mass which developed in a maxillary sinus.

Demography of an Undergrowth Palm in Littoral Cameroon

This study of Podococcus barteri in Cameroon, equatorial West Africa, shows that the longevity of this small palm is in the range of 63-74 years. Seasonality is more pronounced in flowering than in leaf production. Adults produce one leaf per year, each lasting about five years in the crown. Proliferation by stolons begins many years before flowering. The leafy stolons may grow two-eight or more years before establishing the ramets. Inflorescence development, flowering, and seed maturation take about 1.4 years. Only 0.08 percent of the ovules become mature seeds. A stage projection matrix gives the annual population growth rate as 1.2 percent. The growth index X is more sensitive to changes in mortality of juveniles and young adults than of seeds-seedlings, mature-old adults, or stolons. Mortality at several stages of sexual reproduction and the size advantage of ramets account for the greater importance of cloning to population dynamics, although the relative energetics have not been assessed. IN LOWLAND WET FORESTS, the occasional disruption of the deep-shade and sunfleck environment by falling trees results in luxuriant growth of many species. Tree-fall gaps have been considered the main organizing feature of population and community dynamics (Aubreville 1938, Jones 1956, Whitmore 1975, Hartshorn 1978). The pattern of spatial and size distributions of many species reflects the focus of their establishment and/or maturation in gaps, but other species do not conform (e.g., Richards and Williamson 1975). The comparatively sparse plant cover of the long-enduring, abysmal gloom of the floor of mature forest has been largely ignored even in vegetation studies, and the growth and reproductive behavior of this flora is virtually unknown despite its accessibility. Palms are a particularly abundant part of this lower stratum, and convenient to study as their geometric simplicity much facilitates observation and analysis of their behavior. Even for relatively longlived species, demographic projections can be made from short-term observations (Hnatiuk 1977, Van Valen 1975 based largely on Bannister 1970). In contrast to the diversity of small palms in Malayan and American forests (Whitmore 1973, Moore 1973a), there are only two species in mature forest undergrowth in Africa. Podococcus barteri is occasionally common in the littoral region of Cameroon, growing in clusters often of 10-4 or 10-3 ha, with stem densities up to seven per m2. The habit, distribution, growth, and reproduction of Podococcus will be described here, with the purpose of assessing seasonality, the time scales relevant to individual life history, the stability of the population (of plant modules, not genets), and its sensitivity to disturbance of existing growth, reproduction, and mortality schedules. Demographic treatment of long-lived woody plants lags far behind that of herbs (Harper 1977), and is of particular interest for Podococcus as a species of the mature phase of lowland forest, and one which both clones and produces seed.

Flowering, pollination and fruiting in Zostera marina L.

Sexual reproduction of Zostera marina L. has been observed in vitro. Six different stages can be distinguished: (1) the styles erect from the spadix and (2) bend back after pollination with the thread-like pollen grains; (3) pollen is released from the half anthers under water or at the water surface; (4) after maturation of 4 to 5 weeks, (5) the seeds are released from the fruit, the fruit wall remaining fixed on the spadix; (6) withering starts a few days before the release of the seeds and the flowering shoot is generally uprooted at the end of the flowering season. The time sequence of the stages of sexual reproduction is given.

Competition on Marine Hard Substrata: The Adaptive Significance of Solitary and Colonial Strategies

Most solitary and colonial animals inhabiting marine hard substrata differ fundamentally in their ability to use space. Colonial animals are superior space competitors because (1) indeterminate growth allows continuous lateral substratum occupation without requiring intervening stages of sexual reproduction and recruitment, and (2) they are less susceptible to fouling and overgrowth. Solitary animals survive in the seas because (1) various morphological and behavioral attributes (escape in size, aggregative behavior) protect them in spatial competition with colonial animals or because (2) predation, physical disturbance, or competition with plants prevents monopolization of substrata by colonial animals. Focus on ecological strategies circumvents arguments regarding the solitary or colonial identity of problematical groups such as sponges. The evolution of specific competition mechanisms by colonial animals has provided the basis for competitive networks which have further favored the evolution of highe...

Sexal reproductive cycle of Monascus in submerged shaken culture.

A strain of Monascus was grown in submerged, shaken culture using a glucose-salts mediumn. The formation of ascospores was studied by microscopic examination of samples taken at regular intervals for 6 days. All the stages of sexual reproduction previously described for Monascus were observed. The unusual feature of the strain studied was that it produced sexual structures and cliestothecia of greatly varying sizes.

The localization of some enzymes in the mycelium of Mucor hiemalis.

Histochemical staining for dehydrogenases in mycelium of Mucor hiemalis has shown characteristic localizations of these enzymes. Alcohol dehydrogenase is almost totally localized in the chlamydospores, in developing sporangia and in the columellae of intact and ruptured sporangia. Malate, isocitrate (NAD-and NADP-linked) and glutamate (NAD- and NADP-linked) dehydrogenases are localized in hyphae showing the early stages of sexual and asexual reproduction.

Role of Nitrogen Concentration on Production of Perithecia in Penicillium vermiculatum Dangeard

SEXUAL reproduction is sometimes dependent on a number of environmental factors. While some fungi normally pass from the vegetative stage to the sexual reproduction stage regardless of their environment, there are others which will not undergo sexual reproduction unless provided with specific external factors, physical or chemical. Hawker1 demonstrated that both thiamine and biotin are essential for sexual reproduction of Melanospora destruens. In the same species she also found a differential effect on sexual reproduction by a number of carbon sources. Other workers2, experimenting with a number of fungal species, have found numerous other factors to be beneficial or indispensable for sexual reproduction.

VENTURIA INAEQUALIS (CKE.) WINT. I. A GROUNDWORK FOR GENETIC STUDIES

VENTURIA INAEQUALIS (CKE.) WINT. I. A GROUNDWORK FOR GENETIC STUDIES