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41.
Jean-Claude Wissocq Catherine Heurteaux Elisabeth Hennequin Michel Thellier 《Development genes and evolution》1985,194(7):433-435
Summary The quantitative imaging of lithium distribution, in histological sections of 15-days old mouse embryos (whose mother had been submitted to Li-treatment), was performed using6Li isotope as tracer,6Li(n,)3H nuclear reaction for detection, and dielectric track detectors. Despite the particular difficulties of cryosectioning the embryos without disturbing the lithium distribution, the Li regionalization appeared to be very clear-cut. The ectomesodermic tissues were significantly more loaded with lithium than the endodermic ones. This is probably related to the ectomesodermic tissues being also those most sensitive to the teratogenic effect of lithium. The Li-distribution in the embryo brain was almost homogeneous, instead of being heterogeneous as in adult brain. The mean Li-concentration in the embryo brain was not much below the Li concentration in the grey matter of the mother brain, but it was significantly larger than that in the white matter of the mother brain. Our results are discussed in the context of teratogenic effects observed in situ during mammalian development. 相似文献
42.
Computer simulations are used to predict the behavior of pollen grains with different physical properties within the acceleration field created around the ovules of the gymnosperm Ephedra trifurca. A modelling procedure is given that (1) calculates the number of pollen grains captured by an ovule's pollination-droplet and (2) gives a correlation between pollination efficiency and the physical properties (= mass, size) of different types of pollen. Based on this procedure, the number of Ephedra pollen grains captured by micropyles can be less than the number captured from other species. However, the mass and size of Ephedra pollen grains appear to coincide with those predicted to yield a local maximum of pollination efficiency, i.e. slightly larger or smaller values of either mass or size would decrease the probability of capture. In addition, the properties of Ephedra pollen grains operate synergistically in the aerodynamic environment around ovules and are focused to collide with pollination-droplets. By analogy, the properties of Ephedra pollen coincide with those predicted for a localized adaptive peak. The physical properties of pollen grain types other than E. trifurca that can maximize pollen capture are not generally represented in the aerobiology of Ephedra during the pollination season. Therefore, the phenology of pollen release, community taxonomic-composition, and the physics of particle capture play collectively important roles in the reproductive success of Ephedra trifurca. 相似文献
43.
Three co-existing pollination mechanisms are found inUrginea maritima: insect-, wind-, and self-pollination. The flowers exhibit a typical insect-pollination syndrome; they offer abundant exposed nectar as well as pollen. Out of the many different visitors only a few could be regarded as pollinators:Apis mellifera, Polistes gallicus, andVespa orientalis. Wind pollination also occurs and generally is responsible for self-pollination.It is argued that the development of extra wind-pollination accompanied by partial self-incompatibility is an adaptation to increase pollination in an unfavourable season (August–September), when insects are scarce. 相似文献
44.
V. Formicola 《Human Evolution》1986,1(6):557-563
Late Epigravettian postcranial human remains from the Arene Candide cave (Finale Ligure, Savona, Italy) were compared with
the Neolithic sample found in the upper levels of the same site. Data on length, diaphyseal circumference and diameter of
clavicle, humerus, radius, femur and tibia were collected from male specimens having all these bones. The Epigravettian sample
is characterized by significantly greater tibial length, robustness and platycnemia, significantly lower circumferences in
the upper limb bones and the clavicle, and a high degree of asymmetry. Variations observed in lower limb bones are those expected
on the basis of the different functional requirements of a hunting and gathering economy compared to a more sedentary, food
producing economy. Differences in the upper limb bones and the clavicle are less explicable. However, considering that in
spite of a more slender structure, the Epigravettian bones show evidence of vigorous use, variation in upper limb could result
from qualitatively different involvements. 相似文献
45.
46.
In the savanna around Lamto,Caryedon serratus develops, in the beginning of the dry season, on maturing seeds ofPiliostigma thonningii (Caesalpinioideae). A 2nd generation, and sometimes a 3nd one, develops in dry seeds. There is no pupal diapause during the rainy season and adults seems to spend this period in a
semi-lethargic state. The parasitoid complex ofC. serratus is a chalcid-dominated one. It includes 5 species: one oophagous (Uscana caryedoni) and 4 larvo-nymphal parasitoids. Three species are regular (Anisopteromalus caryedophagus, Bracon sp. andU. caryedoni), the others are sporadic species (Proconura serratocida, Eurytoma caryedocida). Biological data are given for each species.
相似文献
47.
J. H. N. Schel 《Sexual plant reproduction》1989,2(1):59-64
Summary Exactly 150 years after the publication of the so-called cell theory the role of the botanist Schleiden has been reconsidered. It is emphasized that the study of plant sexual reproduction systems has contributed considerably to the development of the general cell concept. Recent examples show that 150 years later plant cell biology is flourishing, not least because of the great impact of the increasing use of plant reproductive cells and organs. 相似文献
48.
49.
Fiedler K 《Oecologia》1990,83(2):284-287
Summary Fourth instar larvae of Polyommatus icarus maintain myrmecophilous associations with ants. In laboratory experiments, the attractiveness of larvae reared on foliage of the tree Robinia pseudacacia was significantly reduced compared with caterpillars fed with herbaceous Fabaceae. The ability to secrete carbohydraterich liquids from the dorsal nectary organ was also strongly reduced, while the function of the tentacle organs remained unaffected. The reductions in attractiveness and secretion abilities are caused by the food quality itself and not by secondary effects such as reduced larval size. The ecological significance of the results are discussed with respect to facultatively and obligately myrmecophilous lycacnids. 相似文献
50.
Summary A structural study of pollination in the dimorphic flowers ofCollomia grandiflora, a cleistogamous species, reveals significant differences in stigma behavior during pollination, stylar structure, the timing of generative cell division, and pollen tube growth rate patterns. The cleistogamous flower shows a loss of protandry and the stigma is receptive only after reflexing and closing of its lobes. In contrast, the chasmogamous stigma is receptive when reflexed and closes when pollen has been deposited on the lobes. Pollen tube penetration of the dry stigma papillae and entry into the style is similar in the two morphs. The chasmogamous style is solid and the cleistogamous style partly hollow. The matrix of secretion produced by the transmitting tract cells is mainly carbohydrate with a trace of lipids. It is fibrillar in nature and appears to be partly comprised of wall material from the transmitting tract cells. In the chasmogamous pollen, the generative cell enters the tube before division, which occurs between 30 and 60 min after pollination. This division correlates with an increased growth rate for the pollen tube. In the cleistogamous pollen, contact with the stigma triggers generative cell division inside the hydrated pollen grain before germination. The two resulting sperm cells exit the grain 15–30 min after pollination when the pollen tube is in the stigma lobes. The cleistogamous pollen tube shows only one phase of growth which occurs at a rate similar to that of the slow, first phase of the chasmogamous pollen.Abbreviations CH
chasmogamous
- CL
cleistogamous
- DAPI
4, 6-diamidino-2-phenylindole 相似文献