Female parthenogenetic apomixis and androsporogenesis in Douglas-fir embryonal initials in an artificial sporangium

Control of female parthenogenetic apomixis and androsporogenesis of Douglas-fir embryonal initials was studied using an experimental culture system in which changes in growth condition can mediate changes in cell identity and outcomes. This culture system constitutes an artificial sporangium in which myriad culture conditions can be simulated and should be applicable for research on a variety of gymnosperms. In this study, embryonal initials from developing seeds from two Douglas-fir trees were rescued and became reprogrammed for female parthenogenetic apomixis (fPA) and parthenogenetic androsporogenesis (mPA). Female PA was initiated by endomitosis forming a binucleate cell with a diploid egg-equivalent and an apoptotic ventral canal nucleus in an archegonial tube. Egg-equivalent nuclei formed cells (parthenotes) that were discharged into an aqueous culture medium. Parthenotes developed axial tiers atypical of early embryogenesis in seeds. Earlier in the year, androsporangial tubes were parthenogenetically differentiated and released monads, dyads, triads, and tetrads into the culture medium. Spores showed chromosomal aberrations. PA demonstrated a temporal separation in gender expression (dichogamy). Embryonal initials brought forward and by-passed the long juvenile phases normally needed for cells to develop into trees and express reproductive maturity. Expressions of fPA and mPA indicated that the specialized culture flasks served as an artificial sporangium (AS). Awareness is raised for the value of an AS for research in gymnosperm life cycles and as a teaching and research laboratory.     

Reproductive fitness consequences of progenesis: Sex‐specific pay‐offs in safe and risky environments

Progenesis is considered to have an important role in evolution because it allows the retention of both a larval body size and shape in an adult morphology. However, the cost caused by the adoption of a progenetic process in both males and females remains to be explored to explain the success of progenesis and particularly its biased prevalence across the sexes and environments. Here, through an experimental approach, we used a facultative progenetic species, the palmate newt (Lissotriton helveticus) that can either mature at a small size and retain gills or mature after metamorphosis, to test three hypotheses for sex‐specific pay‐offs of progenesis in safe versus risky habitats. Goldfish were used because they caused a higher decline in progenetic than metamorphic newts. We determined that progenetic newts have a lower reproductive fitness than metamorphic newts. We also found that, when compared to metamorphs, progenetic males have lower reproductive activity than progenetic females and that predatory risk affects more progenetic than metamorphic newts. By identifying ultimate causes of the female‐biased sex ratios found in nature, these results support the male escape hypothesis, that is the higher metamorphosis rate of progenetic males. They also highlight that although progenesis is advantageous in advancing the age at first reproduction, it also brings an immediate fitness cost and this, particularly, in hostile predatory environments. This means that whereas some environmental constraints could favour facultative progenesis, some others, such as predation, can ultimately counter‐select progenesis. Altogether, these results improve our understanding of how developmental processes can affect the sexes differently and how species invasions can impair the success of alternative developmental phenotypes.     

Observations on the Neocytoplasm and Proteid Vacuoles During the Fertilization of Keteleeria evelyniana

Distributions and dynamics of the neocytoplasm and proteid vacuoles during the fertilization of Keteleeria evelyniana were studied by histochemical methods. Before fertilization cytoplasmic sheath surrounding the male and female gametes was indistinct. After fertilization, the dense neocytoplasm appeared around the zygote. Part of the neocytoplasm is invaded by mitochondria of maternal origin which had collected in large numbers in the perinuclear zone. The mitochondria contain electron compact little body which looks like a nucleus in the cytoplasm, but not observed in the rosette tier cell of proembryo and jacket cells. Hence, it was showed that the neocytoplasm participated in the development of embryo by all these observations. By using Feulgen reaction, the staining reaction of neocytoplasm was positive, the egg nucleus or zygote nucleus was weaker in positive reaction, while the proteid vacuoles were negative. When the proembryo developed, there were a few starch grains accumulated in the other three tiers except the upper tier. The Feulgen reaction was in- creased in intensity in the suspensor tier and embryonal cell tier nuclei. When the young embryo developed, Feulgen reaction became normal in the nuclei of the embryo initials. The embryo initials and Suspensor cells showed very weak Feulgen positive reaetion in the proembryo and young embryo. The development of the large proteid vacuoles was from plastid. During the early stage of egg nucleus, contents of large proteid vacuoles were less. When the zygote was formed, they reached the highest. However, after the zygote produced, the proteid vacuoles and egg cytoplasm were getting disintegrated following the course of fission of free nuclei. After the proembryo formed, the proteid vacuoles were wholly disintegrated.     

A Histological Study of the Development of Buds,Roots, and Embryos in Organ Cultures of Petunia inflata R. Fries

Organ cultures of Petunia inflata R. Fries have displayed adiversity of morphogenetic responses such as rhizogenesis, budformation, and embryo development. Studies oriented towardsdetermining the histological pathways preceding the morphogeneticexpression have indicated that bud formation and rhizogenesiswas always preceded by the establishment of a peripheral meristem.Embryos originated from cytoplasm-rich embryonal initials andthe pattern of their development simulated relatively closelywith the zygotic embryogenesis.     

Dormant stages of the green flagellate Volvox in a natural habitat

Reproduction and formation of resistant dormant spores in Volvox aureus (Ehr.) and V. tertius (Meyer) were studied in a biocoenosis of a transient pool in July-August 1996 and 1997. Under these conditions, the populations of two Volvox species had species-specific reproductive features. In the V. tertius population, a relatively small amount of male individuals and dormant spores (zygospores) appeared sporadically. On the contrary, in the V. aureus population, dormant parthenospores were formed, but male individuals were never observed.     

云南油杉受精过程中新细胞质及蛋白泡的动态观察

云南油杉(Keteleeria evelyniana Mast)在受精前,精核与卵核周围的细胞质鞘不明显。受精后,合子核周围出现细密的新细胞质。应用孚尔根核染色法,可以较清晰地将新细胞质染出,呈现较弱的正反应,而合子的核质及受精前的精核与卵核染色极弱。卵细胞质及其中的蛋白泡均为负反应。原胚形成后,除上层外,其余几层细胞质内开始积累淀粉粒。此时胚原细胞核的孚尔根染色深度有所增加。幼胚形成后,在顶端的胚原细胞群中核的孚尔根染色反应已恢复正常。在原胚及幼胚胚原细胞质中也呈现很弱的正反应。在电镜下,胚原层细胞质及新细胞质中均含有核样电子致密小体或称作染色质小体,而原胚莲座层细胞质及四周套细胞质中的线粒体则不含这种核样小体。因此,大蛋白泡在卵核形成的早期数量不多,当合子形成时含量最高,而随着游离核的分裂进程,蛋白泡以及原卵质均逐渐地解体,在原胚形成后全部消解。     

Timing of epiphyseal development in the flipper skeleton of the harbour porpoise (Phocoena phocoena) as an indicator of paedomorphosis

Epiphyseal development was investigated on X‐rays of flippers from 158 harbour porpoises from Danish waters. Development followed a proximodistal pattern similar to what is known in other cetacean species. Ossification of epiphyses was rare in the phalanges of the first and fifth digits and in the more distal phalanges of the second, third and fourth digits. Along with the morphology of the first metacarpal and the more distal phalanges this suggested paedomorphosis relative to delphinids. Male and female porpoises showed similar progression of epiphyseal development until approximately the sixth year. From then on, female porpoises showed more progressed development than males. This suggests a higher level of paedomorphosis in the male porpoise. The mechanism behind phocoenid paedomorphosis seems to be progenesis, probably as an adaptation towards a high reproductive rate relative to the delphinids.     

银杏雌雄配子体发育及胚胎形成的研究进展

银杏(Ginkgo biloba)是现存最古老的裸子植物之一, 其生殖过程表现出许多原始特征和独特性状, 长期以来备受国内外专家的关注。经过近100年的研究取得了显著成果: (1) 银杏雄配子体发育周期长, 经历了从平周分裂到斜背式分裂,并最终垂周分裂形成带有鞭毛的游动精子; (2) 银杏雌配子体发育经历较长的游离核期和细胞化期, 分化形成颈卵器母细胞并经平周分裂、垂周分裂和斜向分裂形成成熟的颈卵器(包括有4个颈细胞和1个卵细胞); (3) 推测其精细胞中的液泡状结构为受精过程中的遗传物质载体; (4) 原胚的形成经历了游离核期和细胞化期。该文针对国内外最新银杏生殖生物学方面的研究进展, 对银杏雌雄配子体发育、受精过程以及胚胎形成等方面进行较为系统全面的分析和总结, 为进一步的银杏生殖生物学研究提供有价值的参考资料。     

Ultrastructure of auxiliary and gonimoblast cells during carposporophyte development in the red alga Cryptopleura ruprechtiana (Delesseriaceae, Ceramiales, Rhodophyta)

The ultrastructure sequence for the complete post-fertilization development is described in Cryptopleura ruprechtiana (C. Agardh) Kylin, a member of the Delesseriaceae. Following fertilization the diploid nucleus is transferred to the auxiliary cell. This contains typical red algal proplastids, cytoplasmic concentric membranes, numerous small vacuoles and lipid bodies. Crystalline inclusions and virus-like particles are also present. In addition darkly staining spherical masses possibly represent dehydrated haploid chromatin. The multinucleate auxiliary cell produces initially one large gonimoblast initial and subsequently many smaller gonimoblast initials. The first formed generative gonimoblast cell is similar in cellular structure to the auxiliary cell. Gonimoblast initials are uninucleate but through caryokinesis they become multinucleate. They undergo repeated cleavage to form more gonimoblast cells. Subsequent, centripetal cytokinesis results in the formation of clusters of gonimoblast cells. A new type structural cap or association is observed in the septal plugs that interconnect gonimoblast initials. Terminal or generative gonimoblast cells cleave to form additional gonimoblast cells. Only terminal gonimoblast cells are differentiated to carpospores.     

MORPHOLOGY AND DEVELOPMENT OF AHNFELTIA PLICATA (RHODOPHYTA): PROPOSAL OF AHNFELTIALES ORD. NOV.1

Ahnfeltia plicata (Hudson) Fries, the type species of Ahnfeltia Fries, is currently assigned to the Phyllophoraceae (Gigartinales). Several morphological and biochemical characters distance A. plicata from the Phyllophoraceae but, because sexual reproduction has never been demonstrated, an alternative placement has not been possible. A. plicata now is shown to have a heteromorphic sexual life history. Erect branched gametophytes are dioecious. In male sori, spermatangia are cut off transversely from spermatangial mother cells. Female sori form numerous terminal sessile carpogonia. Following fertilization, several zygotes in each sorus fuse facultatively with undifferentiated intercalary cells of the female sorus and cut off gonimoblast initials obliquely outwards. These initials give rise to branching gonimoblast filaments that fuse with apical and intercalary female sorus cells and with each other, then grow radially outward in the compound external carposporophyte and terminate in carposporangia. Carpospores develop in culture into crustose tetrasporophytes identical to Porphyrodiscus simulans Batters. Field-collected P. simulans tetraspores grew into erect A. plicata axes. Tetrasporangia are formed by division and enlargement of crust apical cells followed by sequential enlargement and maturation of tetrasporocytes in an erosive process. Monosporangia are formed in sori on male gametophytes. Pit plugs of both gametophyte and tetrasporophyte phases consist of naked plug cores without cap layers of membranes. Gametophytes exhibit both cell fusions and secondary pit connections whereas tetrasporophytes form cell fusions but lack secondary pit connections. On the basis of the unique female and postfertilization reproductive development and in conjunction with the pit plug structure which is unique among florideophytes, the order Ahnfeltiales, containing the family Ahnfeltiaceae, is proposed.     

Life history constraints on the evolution of abbreviated life cycles in parasitic trematodes

Abbreviations of the complex life cycle of trematodes, from three to two hosts, have occurred repeatedly and independently among trematode lineages. This is usually facultative and achieved via progenesis: following encystment in the second intermediate host, the metacercaria develops precociously into an egg-producing adult, bypassing the need to reach a definitive host. Given that it provides relatively cheap insurance against a shortage of definitive hosts, it is not clear why facultative progenesis has only evolved in a few taxa. Here a comparative approach is used to test whether progenetic trematodes are characterized by larger body size and egg volumes, two traits that correlate with other key life history features, than other trematodes. These traits may constrain the evolution of progenesis, because precocious maturation might be impossible when the size difference between the metacercaria and a reproductive adult is too large. First, trematode species belonging to genera in which progenesis has been documented were found not to differ significantly from other trematode species. Second, using within-genus paired comparisons across 19 genera in which progenesis has been reported, progenetic species did not differ, with respect to body size or egg size, from their non-progenetic congeners. Third, using intraspecific paired comparisons in species where progenesis is facultative, no difference was observed in the sizes of eggs produced by worms in both the intermediate and definitive host, suggesting that opting for progenesis does not influence the size of a worm's eggs. Overall, the lack of obvious differences in body or egg size between trematodes with truncated life cycles and those with the normal three-host cycle indicates that basic life history characteristics are not acting as constraints on the evolution of progenesis; trematodes of all sizes can do it. Why facultative progenesis is not more widespread remains a mystery.     

Capitula in the Asteridae: A widespread and varied phenomenon

The presence of capitula, the head-type of inflorescences, is widespread in the Asterideae. Several families, predominantly terminal in the clade, display the tendency of maximizing reproductive output by condensing indeterminate inflorescences to the point of capitulum formation. This is accomplished by the process of halting or suppressing development of the internodes, an example of paedomorphosis of the progenesis type. This tendency is either infrequent or absent in the basal members of the Asteridae. When inflorescence condensation is present, closely related taxa often demonstrate the progression of the paedomorphosis. More examples of capitulum formation are found in the more advanced families, culminating with the Asteraceae, almost all of which display fully condensed capitula of some sort. Other phenomena are also apparent besides the basic inflorescence condensation. Edge effects are often seen, ranging from a mere crowding of the outermost flowers to the formation of additional flower types. In some taxa, inflorescence condensation continues beyond the basic capitulum form, yielding even more condensed inflorescences that then become determinate. More highly condensed inflorescences have independently evolved several times in the Asteraceae, and some tertiarily condensed inflorescences have evolved as well.     

EFFECT OF TEMPERATURE ON GERMINATION OF RHIZOCLONIUM RIPARIUM (SIPHONOCLADALES,CHLOROPHYTA) AKINETES AND ZOOSPORES1

The temperature requirements for germination by reproductive initials of Rhizoclonium riparium (Roth) Harv., a filamentous green alga, were investigated in laboratory culture. Akinetes and zoospores were produced by exposing aging cultures to high temperatures (40°C). Germination proceeded rapidly and followed a typical bell-shaped response curve, with germination optima between 15 and 20°C. These findings follow the trend found in related algae, i.e. reproductive initials are produced under stressful conditions.     

ONTOGENY OF SEXUAL CONCEPTACLES IN A SPECIES OF BOSSIELLA (CORALLINACEAE)1

The first evidence of conceptacle formation in male and female plants of Bossiella californica ssp. Schmittii is the secretion of a cap below the epithallium. Subsequent development involves the disintegration of the upper enucleate parts of cortical cells below the center of the cap concomitant with the growth of tissue surrounding these cells. Protoplasts in the lower parts of these cortical cells recover and become initials of reproductive cells. Differentiation of each initial in female plants results in a supporting cells bearing 1 or 2, 2-celled carpogonial filaments, and in male plants results in a basal cell bearing 2 or 3 spermatangial mother cells which bud off spermatangia. Following fertilization, supporting cells fuse and form a broad, thin fusion cell from the upper surface of which gonimoblast (carposporangial) filaments arise.     

Differentiation of germinal and somatic cells in Volvox carteri

Volvox carteri is a spherical alga with a complete division of labor between around 2000 biflagellate somatic cells and 16 asexual reproductive cells (gonidia). It provides an attractive system for studying how a molecular genetic program for cell-autonomous differentiation is encoded within the genome. Three types of genes have been identified as key players in germ-soma differentiation: a set of gls genes that act in the embryo to shift cell-division planes, resulting in asymmetric divisions that set apart the large-small sister-cell pairs; a set of lag genes that act in the large gonidial initials to prevent somatic differentiation; and the regA gene, which acts in the small somatic initials to prevent reproductive development. Somatic-cell-specific expression of regA is controlled by intronic enhancer and silencer elements.     

Cellular mechanisms of estradiol-mediated masculinization of the brain

The sexual differentiation of reproductive physiology and behavior in the rodent brain is largely determined by estradiol aromatized from testicular androgens. The cellular mechanisms by which estradiol masculinizes the brain are beginning to emerge and revealing novel features of brain development that are highly region-specific. In the preoptic area, the major site controlling male sexual behavior, estradiol increases the level of the COX-2 enzyme and its product, prostaglandin E2 which promotes dendritic spine synaptogenesis. In the ventromedial nucleus of the hypothalamus, the major site controlling female reproductive behavior, estradiol promotes glutamate release from synaptic terminals, activating NMDA receptors and the MAP kinase pathway. In the arcuate nucleus, a major regulator of anterior pituitary function, estradiol increases GABA synthesis, altering the morphology of neighboring astrocytes and reducing formation of dendritic spines synapses. Glutamate, GABA and the importance of neuronal-astrocytic cross-talk are emerging as common aspects of masculinization. Advances are also being made in the mechanistic basis of female brain development, although the challenges are far greater.     

The effects of blinding,pinealectomy and exposure to constant dark conditions on gonadal activity in the female goldfish,Carassius auratus

Synopsis The effects of pinealectomy, blinding, and exposure to constant darkness were examined in female goldfish during different seasons. Neither blinding nor pinealectomy under short or decreasing photoperiod conditions, nor exposure to constant darkness had an effect on ovarian activity in goldfish during fall and winter. In spring, constant darkness has an inhibitory effect on ovarian activity. Pinealectomy under increasing photoperiod conditions partially inhibits reproductive activity, but not to the extent of constant darkness. Blinding, under the same regime also inhibited to some extent the ovarian response to increasing photoperiod. Our data suggest that retinal pathways and the pineal organ are involved in the photosexual response to increasing day lengths.Address correspondence to: Dr. V. L. de Vlaming, Marquette University     

Dormant Stages of the Green Flagellate Volvox in a Natural Habitat

Reproduction and formation of resistant dormant spores in Volvox aureus (Ehr.) and V. tertius (Meyer) were studied in a biocoenosis of a transient pool in July–August 1996 and 1997. Under these conditions, the populations of two Volvox species had species-specific reproductive features. In the V. tertius population, a relatively small amount of male individuals and dormant spores (zygospores) appeared sporadically. On the contrary, in the V. aureus population, dormant parthenospores were formed, but male individuals were never observed.     

The Gametophytes and Fertilization in Pseudotaxus

The development of the gametophytes and fertilization of Pseudotaxus chienii Cheng has been investigated. Pollination first occurred on April 17 (1964). The pollen grains shed at the uninucleate stage and germination on the nucellus is almost immediate. The pollen tubes approached the freenucleate female gametophyte about May 5. The spermatogenous cell is continuously enlarging with the growth of the pollen tube and two unequal sperms are formed after its division. Occasionally the small sperm may divide further into two smaller ones. During pollination the megaspore mother cell is in meiosis and 3 or 4 megaspores are formed. Generally 2 or 3 megaspores at the micropylar end are going to degenerate while the chalaza] megaspore is rapidly enlarging. After 8 successive simultaneous divisions of the functional megaspore 256 free nuclei are resulted and they are evenly distributed at the bulge of the famale gametophyte. Then the wall formation follows. Sometimes there are more than two, even as many as 5–6 gametophytes developed within a single ovule. The archegonial initials become differentiated at the apical end of the female gametophyte. They are usually single and apical, rarely lateral in position. The number of the archegonia vary from 3 to 7, usually 4–6. There are 2–8 neck cells in each archegonium which is surrounded by a layer of jacket cells. The central cell divided about May 20–26 (1964) and the division of the central cell gives rise to the egg and the ventral canal nucleus, the latter being degenerated soon. There are many proteid vacuoles near the nucleus of the matured egg. The fertilization took place about May 23–26 (1964). At first, the pollen tube discharges its contents into the egg, then the larger sperm fuses with the egg nucleus in the middle part of the archegonium. At the same time the male cytoplasm also fuses with the female cytoplasm and a layer of densely-staining neocytoplasm is formed around the fused nucleus. The smaller sperm, tube nucleus and sterile cell usually remain in the cytoplasm above the egg nucleus for some time. Based upon the observations of the development of the gametophytes and fertilization the authors conclude that Pseudotaxus is more close related to Taxus than any other member of Taxaceae.