Caractères ultrastructuraux du pollen de quelques Podostémales. Affinités avec les Rosidae évoluées

The order Podostemales are two pantropical families of aquatic plants living in running water: Tristichaceae (five genera, ten species) and Podostemaceae (35 genera, 200 species). Pollen of the 26 genera and 62 species studied is characterized by: a granular infratectum in which the granules are sometimes organized as columellae like units, and a lamellar and/or granular endexine in all pollen types, single or in dyads. Most of the apertural characters and the ornamentation of the exine allow us to distinguish the previously established taxonomic groups: Weddellinoideae have tricolporate rugulo-areolate, pollen with a smooth apertural membrane; in Tristichoideae, pollen is periporate and the microspines of the tectum and of the apertural membrane are massive; in Podostemaceae, the tectal spines with their broad bulbous base are formed from numerous masses of sporopollenin, the endexine is microfibrillar at the base, the apertural membrane is constituted of structured ectexinous masses, and the endexine is granular at the aperture. Presence of the tricolporate pollen type associates the Podostemales with the higher eudicotyledons. Most of the pollen characters of Podostemales and their variations are found among advanced Rosidae (Hamamelidales, Polygalales, Santalales, Violales, Euphorbiaceae).     

The weight-volume relationship of the test of Alveolinella quoyi: Implications for the taphonomy of large fusiform foraminifera

Severin, Kenneth P. & Lipps, Jere H. 1989 01 15: The weight-volume relationship of the test of Alveolinella quoyi: Implications for the taphonomy of large fusiform foraminifera. Lethaia , Vol. 22, pp. 1–12. Oslo. ISSN 0024–1164.
Alveolinella quoyi , the largest living fusiform foraminifer, can be used to infer the paleobiology of extinct fusulinids and alveolinids. We measured test plus organic material weight, test weight, and test volume for A. quoyi , allowing the calculation of test density under various conditions. Tests have an average of 43% chamber space, and an average density of 1.5 gcm^-3. Living individuals can only fill an average of 39% of their chamber space with protoplasm. If they fill the remaining space with sea water, average effective test density is 0.953 gcm^-3, if the space is filled with a gas the density is 0.671 gcm^-3. Living individuals can withstand current velocities of 3–4 m sec^-1, velocities greater than commonly occur in A. quoyi's habitat. Dead tests have lower effective densities than many carbonate sedimentary particles (0.508 g cm^-3 if the chamber space is gas filled, 0.953 g cm^-3 if it is sea water filled), making their settling velocities slow relative to similarly shaped and sized particles. Their large size and high traction velocities (>0.2m sec^-1) makes them unaffected by gentle currents which can remove 100–200 μ sized particles from the sediment. Their low settling velocity will tend to concentrate A. quoyi tests during subsequent resuspension, creating a layer of tests near the sediment-water interface. Concentrations of extinct fusiform foraminifera may have formed in a similar manner. □ Lorger foraminifera, test weight, test volume, test density, taphonomy .     

Structure of the apertural sporoderm of pollen grains inEuphorbia andChamaesyce (Euphorbiaceae)

The tricolporate pollen grains of 38 Mediterranean and Macaronesian species ofEuphorbia L. andChamaesyce S. F. Gray have a special apertural sporoderm not found in the other taxa of theEuphorbiaceae. At the apertural margo the ectexine is thinner because of shorter columellae and the thin, fragmented or even absent foot-layer. Ectexinous granules, mixed with endexinous material, are present near the ora. The endexine is homogeneous and thickened under the colpi (at the end and at the proximity of the end of colpus). Around the ora, the endexine is granulate and lamellar with irregular cavities. The apertural intine presents a characteristic structure with thickenings running along both sides of the colpi. The arrangement and structure of these intinous thickenings depend on the distance from the ora. This special morphology of the intine is present in all taxa studied here. The genusEuphorbia is considered to be the most evolved taxon of this family. The characteristic apertural sporoderm may be an adaptative modification to different physiological conditions, so it may present an apertural mechanism which is more adapted to harmomegathic changes and thus facilitate the germination and the formation of the pollen tube.     

Gamete structure and fertilization in the brown alga Hormosira banksii (Turner) Decaisne

Light microscope and fine structural studies of the gametes of Hormosira banksii show the antherozoids as typical Fucales biflagellate gametes with a posterior whiplash flagellum and an anterior flagellum with mastigonemes. The oospheres are enclosed in a plasma membrane, are highly vacuolate and contain abundant phenolic inclusions.

Antherozoids attach to the surface of the oospheres by their anterior flagellum at conjugation. Following fertilization Golgi derived vesicles underlying the plasma membrane decrease in electron density and an exterior surface coat appears outside this membrane. This may be a “fertilization barrier” which prevents further penetration by other male gametes.

Subsequently a fibrous layer appears which develops into a cell wall around the developing zygote. Histochemical studies show the cell wall of these young zygotes is probably made up of alginic acid. Fine structural and histochemical examination of the young zygotes suggest that whereas there is no preformed adhesive in the oosphere, large reserves of lipid and polysaccharide provide materials necessary for synthesis of wall material and the potential for adhesive production following fertilization.     

ULTRASTRUCTURE OF CEPHALEUROS VIRESCENS (CHROOLEPIDACEAE; CHLOROPHYTA). IV. ABSOLUTE CONFIGURATION ANALYSIS OF THE CRUCIATE FLAGELLAR APPARATUS AND MULTILAYERED STRUCTURES IN THE PRE- AND POST-RELEASE GAMETES

Transmission electron microscopy of pre-release and post-release biflagellate gametes of Cephaleuros virescens has produced comparative data on these cells and on the detailed absolute arrangement of the flagellar apparatus. In all major respects including the presence of two multilayered structures (MLS's) the closely compacted, non-motile but mature pre-release gametes are similar to the mature, free swimming post-release gametes. The elongated shape of the free-swimming gametes differs from the more compact form of the pre-release gametes, but does not reflect a major difference in the arrangement of internal components. The flagella are bilaterally keeled and each keel contains a cylindrical element. Each flagellar base is encircled by a densely staining collar of modified plasmalemma at the point of entry into the apical papilla. The equal anterior flagella enter the papilla from opposite sides; their basal bodies are parallel and overlapping. Each terminates in a densely staining terminal cap. No capping plate is present. Each basal body is associated both with a three-layered MLS, the anterior layer of which becomes a lateral microtubular spline of 2 to 8 microtubules, and with an additional medial compound root of two layers of microtubules (2 over 4 or 5). Both the compound microtubule root and the spline may acquire additional microtubules as they extend distally in close proximity to mitochondria and the plasmalemma. No striated roots, or rhizoplasts, have been observed. Two densely staining plaques are associated with the plasma membrane at specific anterior sites and may be comparable to the presumptive mating structures seen in other green algal motile cells. The reversed bilateral symmetry of the cells produces two possible arrangements of the flagellar apparatus, namely, a 11/5 (or left-handed) arrangement or a 1/7 (or right-handed) arrangement. Only 11/5 cells have been found. Despite the presence of distinct multilayered structures, some aspects of the gametes of Cephaleuros quite closely resemble the cruciate motile cells of algae now regarded by some authors as typical of Ulvophyceae, sensu Stewart and Mattox.     

Benthic origin and earliest evolution of the first planktonic foraminifera after the Cretaceous/Palaeogene boundary mass extinction

There are several hypotheses on the origin and evolution of the earliest Danian planktonic foraminifera. Most experts suggest that they descended from a few opportunist planktonic foraminifera species, mainly of the genera Guembelitria and Hedbergella, which are usually considered to be survivors of the Cretaceous/Paleogene (K/Pg) boundary mass extinction. Nevertheless, early Danian specimens of Guembelitria and Hedbergella remained morphologically well separated from the associated parvularugoglobigerinids (i.e. Parvularugoglobigerina and Palaeoglobigerina), the first trochospiral planktonic foraminifera appearing after the K/Pg boundary event. The most likely alternative is a benthic origin for the parvularugoglobigerinids, which would be consistent with molecular phylogenetic studies that have suggested several episodes of benthic-planktonic transitions in the evolutionary history of planktonic foraminifera. A review of material from the El Kef section and other Tunisian sections supports the previous hypothesis that the buliminid genus Caucasina is the ancestor of the first parvularugoglobigerinids (i.e. Parvularugoglobigerina longiapertura and Palaeoglobigerina alticonusa), on the basis of similarities in test and apertural morphologies and wall texture. The intermediate morphotypes between caucasinids and parvularugoglobigerinids, which appeared approximately 3–5 kyr after the K/Pg boundary, are assigned to Pseudocaucasina antecessor gen. nov. sp. nov.     

Good genes and old age: Do old mates provide superior genes?

It has been suggested that female preference for older mates in species without parental care has evolved in response to an alleged higher genetic quality of older individuals. This is based on the widespread assumption that viability selection produces older individuals that are genetically superior to younger individuals. In contrast, we propose that the oldest individuals rarely are genetically superior. Quantitative genetic models of life history evolution indicate that young to intermediately aged individuals are likely to possess the highest breeding values of fitness. This conclusion is based on four arguments: 1) Viability selection on older individuals may decrease or at least not substantially increase breeding values of fitness, because there may exist negative genetic correlations between late-age and early-age life history parameters, 2) Fertility selection is likely to raise the fitness of gametes produced by young individuals more than those produced by old individuals, because the covariance between fertility and fitness often decreases with age, 3) The history of selection on their parents makes younger individuals more fit than older individuals, 4) Germ-line mutations, which are generally deleterious, significantly decrease the breeding value of fitness of an individual throughout its lifespan, especially in males. Therefore, females that mate with the oldest males in a population are doing so for reasons other than to obtain offspring of high genetic quality.     

L’intégrine α6β1 ovocytaire et spermatique dans l’interaction gamétique

Based on inhibition tests, the α6β1 integrin was suggested to be a sperm receptor, but further experiments using gene deletion techniques have shown that neither oocyte α6, nor β1 integrin subunits were essential for mouse fertilization. Using Western blot analysis and immunofluorescence (flow cytometry and microscopy), we have shown that mouse sperm expresses the α6β1 integrin. As for oocytes, binding of GoH3 anti-alpha6 antibody to sperm induces specific inhibition of sperm fertilizing ability. Comparing zona-intact and zona-free eggs in fusion tests, we have shown that removal of the zona pellucida bypasses the α6β1 integrin role in the adhesion/fusion process of oocyte fertilization. The α6β1 integrin is expressed by both gametes and is functional during their membrane interactions. Our results, previous reports on fertilization of α6 or β1 integrin subunit-deleted oocytes by wild-type sperm and the fusion ability of β1 mutant myoblasts when they were co-cultured with wild-type myoblasts suggest that the presence of α6βl integrin on one of the two gamete membranes can rescue the fertilization process. This hypothesis is further supported by the recently reported exchange of membrane fragments occurring between gametes prior to fusion.     

Distribution of living benthic Foraminifera on the back-reef and outer slopes of a high island (Moorea French Polynesia)

Living foraminifera were examined on both sides of the barrier reef across a section situated on the north-west part of the high island of Moorea (Society Archipelago, French Polynesia). In all, 87 species were found: 62 in the back-reef area (fringing reef, channel and barrier reef) and 72 on the outer slope; 47 were common to both zones. This study points out the importance of substrates in the distribution pattern of foraminifera. The sediments are essentially inhabited by epipsammitic species, whereas algae are colonized mainly by free-living foraminifera: miliolids in the back-reef area; rotaliids in the outer slope. Free-living individuals are much less abundant in the fringing reef, channel and inner part of the barrier reef than in the other parts of the study area. The two major groups on the two sides of the barrier reef are very different in size, test building and probably nutritional modes. In the back-reef area, epipsammitic taxa, mainly composed of small agglutinated species, dominate the fauna; in the outer slope large calcareous symbiotic Amphistegina are the major components of the living association (50 to 70%).     

Gamete membrane dynamics during double fertilization in Arabidopsis

In the double fertilization of angiosperms, one sperm cell fertilizes an egg cell to produce a zygote, whereas the other sperm cell fertilizes a central cell to give rise to an endosperm. There is little information on gamete membrane dynamics during double fertilization even though the cell surface structure is critical for male and female gamete interactions. In a recent study, we analyzed gamete membrane behavior during double fertilization by live-cell imaging with Arabidopsis gamete membrane marker lines. We observed that the sperm membrane signals occasionally remained at the boundary of the female gametes after gamete fusion. In addition, sperm membrane signals entering the fertilized female gametes were detected. These findings suggested that plasma membrane fusion between male and female gametes occurred with the sperm internal membrane components entering the female gametes, and this was followed by plasmogamy.     

Cenozoic record of elongate,cylindrical, deep-sea benthic foraminifera in the North Atlantic and equatorial Pacific Oceans

In the late Pliocene–middle Pleistocene a group of 95 species of elongate, cylindrical, deep-sea (lower bathyal–abyssal) benthic foraminifera became extinct. This Extinction Group (Ext. Gp), belonging to three families (all the Stilostomellidae and Pleurostomellidae, some of the Nodosariidae), was a major component (20–70%) of deep-sea foraminiferal assemblages in the middle Cenozoic and subsequently declined in abundance and species richness before finally disappearing almost completely during the mid-Pleistocene Climatic Transition (MPT). So what caused these declines and extinction?In this study 127 Ext. Gp species are identified from eight Cenozoic bathyal and abyssal sequences in the North Atlantic and equatorial Pacific Oceans. Most species are long-ranging with 80% originating in the Eocene or earlier. The greatest abundance and diversity of the Ext. Gp was in the warm oceanic conditions of the middle Eocene–early Oligocene. The group was subjected to significant changes in the composition of the faunal dominants and slightly enhanced species turnover during and soon after the rapid Eocene–Oligocene cooling event. Declines in the relative abundance and flux of the Ext. Gp, together with enhanced species loss, occurred during middle–late Miocene cooling, particularly at abyssal sites. The overall number of Ext. Gp species present began declining earlier at mid abyssal depths (in middle Miocene) than at upper abyssal (in late Pliocene–early Pleistocene) and then lower bathyal depths (in MPT). By far the most significant Ext. Gp declines in abundance and species loss occurred during the more severe glacial stages of the late Pliocene–middle Pleistocene.Clearly, the decline and extinction of this group of deep-sea foraminifera was related to the function of their specialized apertures and the stepwise cooling of global climate and deep water. We infer that the apertural modifications may be related to the method of food collection or processing, and that the extinctions may have resulted from the decline or loss of their specific phytoplankton or prokaryote food source, that was more directly impacted than the foraminifera by the cooling temperatures.     

Deep-sea benthic foraminiferal recolonization of the 1991 Mt. Pinatubo ash layer in the South China Sea

A census count of Rose Bengal stained benthic foraminifera from the surface area on top of a 2 to 6 cm thick ashfall layer at three deep water stations along the western margin of the Philippines exhibits a unique assemblage composition of benthic foraminifera. The total number of benthic foraminifera is low and the ratio of living individuals to empty tests is high. Specific diversity is low, with a significant dominance of infaunal morphotypes including species of the genus Reophax (R. scorpiurus, R. bilocularis and R. dentaliniformis), which are regarded as successful recolonizers. Assemblages below the ash layers are diverse and contain many epifaunal suspension-feeding agglutinated and calcareous foraminifera. The 1991 Mt. Pinatubo eruption caused mass mortality of benthic foraminifera in a vast area of the eastern South China Sea followed by step-wise recolonization of the ash substrate. Three years after the eruption, the benthic foraminiferal community structure is still far from recovery to background levels.     

SEX‐SPECIFIC CELL SURFACE STRUCTURE OF ANISOGAMETES: MORPHOLOGICAL CHANGES DURING FERTILIZATION OF BRYOPSIS MAXIMA (ULVOPHYCEAE,CHLOROPHYTA) REVEALED BY ULTRA–HIGH‐RESOLUTION FIELD EMISSION SEM1

Cell surfaces of biflagellate gametes and their morphological changes during fertilization of Bryopsis maxima Okamura were observed using a high‐resolution field emission scanning electron microscope. Male gametes have broad and narrow faces, which are divided into at least five morphologically distinct regions: 1) the apical plate is a plate‐like structure that is approximately 380–530 nm long and approximately 190 nm wide, in the center of the papilla and slightly protruded from the plasma membrane; 2) strips are smooth materials on ridges that originate from the basal part of the papilla and extend downward; 3) the lateral belt is a belt‐shaped structure on the center of the narrower faces; 4) the flagellar surface; and 5) the other region of the cell body has a fine‐grained appearance. In contrast, the entire female gamete surface is rough because of many granular or amorphous cell coats on the plasma membrane. When both gametes were mixed together, the initial fusion proceeded between the broader face of the male gamete and the anterior side of the female one near the basal bodies. Morphology of the male gamete's cell surface changed gradually as fusion proceeded and was covered by the granular materials; that surface closely resembled those of female gametes except for the apical plate. It was present until the planozygote attached itself to the substrate by the papilla. It finally disappeared after settlement. Therefore, these results indicate that gametes of B. maxima have sex‐specific surface structures that change their morphology during fertilization and settlement.     

Filipin labeling in Chlamydomonas gametes exposes site-specific lipid specializations.

A thin section study of mating Chlamydomonas cell wall-less CW 15 mating type plus (mt+) and mating type minus (mt-) gametes utilized filipin. The results show extensive labeling of mt+ and mt- plasma membranes. No labeling was seen on the mating structure membranes of activated mt+ or mt- gametes. These results indicate that differences exist between the plasma membrane and the mating structure membrane of gametes. If filipin is specific for the 3-beta-OH sterol, ergosterol and/or other Chlamydomonas sterols, then these results imply that the fusing mating structure membranes may be altered or reduced in sterol content. Such lipid specializations may increase local membrane fluidity and thereby facilitate the site-specific cell fusion associated with mating Chlamydomonas gametes.     

Detection of marker associations with a dominant disease gene in genetically complex and heterogeneous diseases.

Linkage disequilibrium of a marker allele with disease may characterize a chromosomal region containing the disease gene. In several diseases, only a limited number of pedigrees are linked to a particular region, because of linkage heterogeneity. Disequilibrium in this situation is more easily detected when the association is positive (an infrequent marker allele associated with disease mutation), and sampling is conditional on presence or absence of illness in individuals or gametes. Defining H as the marker frequency in illness-transmitting gametes, and Q the marker frequency in normal chromosomes, we compute the power of a given sample (of ill persons/gametes) to detect association in a disease that is genetically heterogeneous, with a dominantly transmitted form linked to a marker. The estimation of Q and the effects of linkage heterogeneity (when unrelated individuals are examined) are also analyzed. Two linked pedigrees give acceptable power to detect association when the allele is frequent enough in illness gametes (H greater than or equal to .6) and infrequent enough in normals (Q less than or equal to .01). If H greater than or equal to .2, 14 pedigrees are needed to give the same power. From the analysis of different values of Q and H, it appears that even in the presence of considerable genetic heterogeneity and complex inheritance (where some normals carry the disease mutation), association may be detected with clinically feasible sample sizes.     

Fusion of membranes during fertilization. Increases of the sea urchin egg''s membrane capacitance and membrane conductance at the site of contact with the sperm

The early events of fertilization that precede and cause activation of an egg have not been fully elucidated. The earliest electrophysiological change in the sea urchin egg is a sperm-evoked increase of the egg's membrane conductance. The resulting depolarization facilitates entry of the fertilizing sperm and precludes the entry of supernumerary sperm. The sequence of the increase in the egg's membrane conductance, gamete membrane fusion, egg activation, and sperm entry, including causal relationships between these events, are not known. This study reports the use of whole egg voltage clamp and loose patch clamp to monitor simultaneously changes of membrane conductance and capacitance at the site of sperm-egg contact. Measurements were made during sperm-egg interactions where sperm entry readily proceeded or was precluded by maintaining the egg's membrane potential either at large, negative values or at positive values. Whenever the sperm evoked an increase of the egg's membrane conductance, that increase initiated abruptly, was localized to the site of sperm attachment, and was accompanied by a simultaneous abrupt increase of the membrane capacitance. This increase of capacitance indicated the establishment of electrical continuity between gametes (possibly fusion of the gametes' plasma membranes). If sperm entry was blocked by large negative membrane potentials, the capacitance cut off rapidly and simultaneously with a decrease of the membrane conductance, indicating that electrical continuity between gametes was disrupted. When sperm entry was precluded by positive membrane potentials, neither conductance nor capacitance increased, indicating that sperm entry was halted before the fusion of membranes. A second, smooth increase of capacitance was associated with the exocytosis of cortical granules near the sperm in eggs that were activated. Electrical continuity between the gametes always preceded activation of the egg, but transient electrical continuity between the gametes alone was not always sufficient to induce activation.     

Membrane differentiations at sites specialized for cell fusion

Fusion of plasma membranes between Chlamydomonas reinhardtii gametes has been studied by freeze-fracture electron microscopy of unfixed cells. The putative site of cell fusion developes during gametic differentiation and is recognized in thin sections of unmated gametes as a plaque of dense material subjacent to a sector of the anterior plasma membrane (Goodenough, U.W., and R.L. Weiss. 1975.J. Cell Biol. 67:623-637). The overlying membrane proves to be readily recognized in replicas of unmated gametes as a circular region roughly 500 nm in diameter which is relatively free of "regular" plasma membrane particles on both the P and E fracture faces. The morphology of this region is different for mating-type plus (mt+) and mt- gametes: the few particles present in the center of the mt+ region are distributed asymmetrically and restricted to the P face, while the few particles present in the center of the mt- region are distributed symmetrically in the E face. Each gamete type can be activated for cell fusion by presenting to it isolated flagella of opposite mt. The activated mt+ gamete generates large expanses of particle-cleared membrane as it forms a long fertilization tubule from the mating structure region. In the activated mt- gamete, the E face of the mating structure region is transformed into a central dome of densely clustered particles surrounded by a particle-cleared zone. When mt+ and mt- gametes are mixed together, flagellar agglutination triggeeeds to fuse with an activated mt- region. The fusion lip is seen to develop within the particle-dense central dome. We conclude that these mt- particles play an active role in membrane fusion.     

Gametogenesis in the Monothalamous Agglutinated Foraminifer Cribrothalammina alba

Gametogenesis in the foraminifer Cribrothalammina alba involves changes in both the gamontic test and cytoplasm. As gametes begin to differentiate and gametic flagella emerge, pores form in a regular array over the gamontic test, constituting the only avenue for gamete release. The spherical, biflagellated gametes average 1.5μ in diameter and are released in rapidly moving swarms along with flagellated “spherical masses” that probably result from incomplete gametic differentiation. Gametogenesis occurs entirely within the test and utilizes the entire cytoplast. After gamete release is complete, the agglutinated test collapses and disaggregates within a fairly short time. Similar modifications of the gamontic test occur during gametogenesis in Ovammina opaca Dahlgren, but are otherwise unknown among monothalamous agglutinated foraminifera at present.     

Adaptations in muscular activation of the knee extensor muscles with strength training in young and older adults

The purpose of this study was to compare the extent of muscular activation during maximal voluntary knee extension contractions in old and young individuals and to examine the effects of resistance training on muscular activation in each group. The interpolated twitch technique was used to estimate muscular activation during two pre-training baseline tests, and after two and six weeks of resistance training. Throughout the study, the older group was 30% less strong than the young group (p=0.02). The training protocol was effective in both groups with overall isometric strength gains of 30 and 36% in the older (p=0.01) and young (p<0.01) groups, respectively. 10-RM training loads increased by 66% in the old group (p<0.01) and by 77% in the young group (p<0.01) throughout training. At the first baseline test, a 2% difference in muscular activation between groups (p=0.3) did not explain the large disparity in strength. Muscular activation increased by 2% in both groups throughout training (p<0.01). Despite considerably less muscular strength in the older group, muscular activation was greater than 95% of maximum and appears to be equal in both young and older individuals. Both groups demonstrated similar but small increases in muscular activation throughout training.     

Taphonomy of larger foraminifera: Relationships between living individuals and empty tests on flat reef slopes (Sesoko Island, Japan)

Summary The depth distributions of larger foraminifera (27 species) were investigated along two transects in the fore reef areas of a NW Pacific fringing reef. One transect is distinguished by a strong flattening below the steep reef slope (−30 m), whereas further steepening characterizes the equivalent part in the other transect. According to the different taphonomic processes affecting foraminiferal tests before final sedimentation, empty tests were classified into the three categories ‘optimally’, ‘well’ and ‘poorly’ preserved. The depth distribution of each preservation state was compared with living individuals. While distributions of optimally preserved tests almost coincide with living individuals, well-preserved tests are characterized by significant depth shifts that are stronger at the upper-most slope compared with the deeper parts. Since the time-averaged traction forces are similar in both investigated transects, differences between the distributions of living individuals and well-preserved tests are more intensive on steep versus flat slopes. Poorly preserved tests signalize allochthonous origin or reworking of relict sediments.