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1.
A biophysical model for buzz pollination in angiosperms   总被引:3,自引:0,他引:3  
The stamens of most of the world's flowering plants are longitudinally dehiscent, releasing their pollen passively, whereupon floral visitors may collect it. In nearly 400 genera in 65 plant families, the anthers dehisce by means of short apical slits or true pores. In these forms, the small light pollen can only be efficiently released by native bees capable of vibrating these stamens. This intrafloral behavior propels pollen out of the pores striking the bees on their venters. It is then collected for use in larval cell provisions. Aspects of the historical development of this novel pollination syndrome, known as “buzz” or vibratile (equals vibrational) pollination, are presented including a discussion and figures of a poricidal anther, a buzzing bee and the model system.A biophysical model for the pollen/locule wall interactions resulting in pollen expulsion upon bee or artificial vibration is developed. The model was created with the morphology of anthers of Solanum (Solanaceae) in mind, but the results obtained are generally applicable to any apically dehiscent flower which is vibrated by bees to release pollen.The anthers were modeled as a tall rectangular box with an apical pore and containing numerous small particles. As the box vibrates, particles striking the walls rebound elastically. If a pollen grain strikes a receding wall, it loses energy. If a grain strikes an advancing wall, it gains energy in the collision. In each oscillation, there is a net gain in the energy of the particles. As the anther (box) is shaken, vibrational energy is transmitted from the pterothorax of the bees to the flower, the pollen grains gaining significant energy. As the energy increases and the particles begin to move about more and more vigorously, they will begin to escape through the hole in the box (or stamina] pore). The rate at which particles leave the box and time required to empty the box are calculated as functions of the geometry of the model system and the frequency of vibration.In order to test the influence of air currents, Bernolli effects and viscous drag, the flowers were mecahnically vibrated in vacuum. The pollen cloud thus produced was virtually unchanged ans so it seems unlikely that air plays any significant role in the phenomenon of vibrational pollen release.Finally, variables such as: inelastic interactions, electrostatic forces, slightly sticky pollen due to presence of “pollenkitt”, duration and types of bee buzzes are discussed in relation to the mathematical model presented.  相似文献   

2.
Self-incompatibility in angiosperms: A review   总被引:2,自引:0,他引:2  
N. T. Arasu 《Genetica》1968,39(1):1-24
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3.
The kingdom of fungi provides model organisms for biotechnology, cell biology, genetics, and life sciences in general. Only when their phylogenetic relationships are stably resolved, can individual results from fungal research be integrated into a holistic picture of biology. However, and despite recent progress, many deep relationships within the fungi remain unclear. Here, we present the first phylogenomic study of an entire eukaryotic kingdom that uses a consistency criterion to strengthen phylogenetic conclusions. We reason that branches (splits) recovered with independent data and different tree reconstruction methods are likely to reflect true evolutionary relationships. Two complementary phylogenomic data sets based on 99 fungal genomes and 109 fungal expressed sequence tag (EST) sets analyzed with four different tree reconstruction methods shed light from different angles on the fungal tree of life. Eleven additional data sets address specifically the phylogenetic position of Blastocladiomycota, Ustilaginomycotina, and Dothideomycetes, respectively. The combined evidence from the resulting trees supports the deep-level stability of the fungal groups toward a comprehensive natural system of the fungi. In addition, our analysis reveals methodologically interesting aspects. Enrichment for EST encoded data-a common practice in phylogenomic analyses-introduces a strong bias toward slowly evolving and functionally correlated genes. Consequently, the generalization of phylogenomic data sets as collections of randomly selected genes cannot be taken for granted. A thorough characterization of the data to assess possible influences on the tree reconstruction should therefore become a standard in phylogenomic analyses.  相似文献   

4.
Summary By inferences from fossil records and circumstantial evidences, it is now generally postulated that angiosperms have a much longer history than hitherto believed and that they have already existed probably in Jurassic time. Studies in vascular tissues and reproductive, structures have negated the possibility of originating angiosperms from various gymnosperm groups. Chronologically, this derivation will be also an impossibility.From a consideration of various aspects in the life history of angiosperms, a hypothesis is here presented postulating that protangiosperms originated in an aquatic or subaquatic environment from an algal ancestry. The enclosure of ovules in the ovary is interpretated as a means of protection necessitated for the transmigration from an aquatic to an aerial habitat for the developing reproductive parts in the bud underwater. Trimery is suggested as a primitive condition, one that affords maximum efficiency in carrying out the purpose under the conditions.In the life history of angiosperms, the endosperm is of great significance in phylogeny. From morphological, physiological, cytological as well as genetical considerations, the endosperm should be regarded as of equal status with the gametophytic and sporophytic generations. There is no comparable structure in the gymnosperm groups and the ferns and fern-allies, while more or less similar conditions are present in the thallophytes. In the long life histories of many red algae, however, there is an especially notable resemblance to angiosperms, with certain details approaching the unique and characteristic features of the endosperms.Land plants are presumably all evolved from aquatic ancestors but instead of the usual concept of a monophyletic origin and lineal development of all vascular plants, a more plausible suggestion is the multiple and recurrent derivation of such plants from various algal ancestral groups. The angiosperms probably represent one of such major lines that originated more or less directly from a thallophytic ancestry.  相似文献   

5.
Angiosperms investigated by DNA/DNA reassociation studies were classified and tested for a taxonomic class- and subclass-specifity in a biometrical fashion. Monocotyledons and Dicotyledons differ significantly from each other with respect to a genomic parameter (U/R-ratio;U single copy DNA fraction;R = 1-U fraction of repetitive DNA). This difference is discussed from an evolutionary and molecular point of view.—Intercorrelations between the fraction of fast repeats, slow repeats, and single copy DNA can be detected. The amount of DNA organized in a short period pattern of interspersion is found to depend on the fraction of repetitive and single copy DNA. The number of DNA segments tandemly arranged in a short period pattern is linearly correlated withR/U-values. This correlation allows for a formula suitable for the estimation of the number of active genes in angiosperms. The analytical complexities of repetitive and single copy DNA are linearly correlated with the genome size of higher plants. The ratioU/R depends on the genome size of angiosperms in a hyperbolic fashion.  相似文献   

6.
Interplate dispersal paths for megathermal angiosperms   总被引:1,自引:0,他引:1  
The dispersal of megathermal angiosperms between tectonic plates is reviewed on the basis of fossil evidence for the Cretaceous and Tertiary periods, since the radiation of the angiosperms, and the period of break-up of Gondwana. The combination of tectonic plate disassembly and redistribution, coupled with phases of global warming followed by pronounced cooling, has resulted in the formation of intermittent dispersal opportunities for frost-intolerant plants, and has been a major factor in determining the direction of angiosperm diversification. The Early Cretaceous radiation of angiosperms seems to show little relationship to the formation of Tethys. However, for the Late Cretaceous and Tertiary nine relevant dispersal routes can be differentiated that can be divided into two distinct categories: routes which formed following the break-up of Gondwana during the Late Cretaceous and Earlier Tertiary, when warm climates encouraged dispersal of megathermal elements globally, and routes which formed since the Middle Eocene, following phases of plate collision, as global climates were cooling down, inhibiting such dispersal. Most inter-plate dispersal of megathermal angiosperms took place in the Late Cretaceous and Early Tertiary at a time when global climates were markedly different from those of today, and the global area of megathermal vegetation several times greater than at present. Under such a scenario, it is likely than opportunities for speciation were much higher than for present-day megathermal plants.  相似文献   

7.
M. R. Rattray 《Hydrobiologia》1995,308(2):117-120
Three species of submersed rooted aquatic angiosperms (Lagarosiphon major, Myriophyllum triphyllum and Potamogeton ochreatus) were grown on nutrient-rich and nutrient-poor sediments in Lake Taupo, an oligotrophic New Zealand lake. Results indicate that plants grown on nutrient-rich sediments had significantly higher shoot tissue concentrations of P, Fe and Mn than those grown on nutrient-poor. High correlations between all three nutrients were recorded for all species. This suggested that the availabilities of P, Fe and Mn in these sediments to these aquatic plants were interrelated.  相似文献   

8.
A revised system of classification of the angiosperms   总被引:20,自引:0,他引:20  
A new system of classification of the angiosperms is presented. Like that of Dahlgren, 1975, it is shown as a two-dimensional diagram or frame-work, but differs in numerous major and minor features. In the new classification the angiosperms represent a class divisible into two subclasses corresponding to the di- and monocotyledons. The dicotyledons are divided into 24 ruperorders, viz . the Magnoliiflorae, Nymphaeiflorae, Ranunculiflorae, Caryophylliflorae, Polygoniflorae, Malviflorae, Violiflorae, Theiflorae, Primuliflorae, Rosiflorae, Podostemoniflorae, Fabiflorae, Proteiflorae, Myrtiflorae, Rutiflorae, Santaliflorae, Balanophoriflorae, Araliiflorae, Asteriflorae, Solanifloirae, Corniflorae, Loasiflorae, Gentianiflorae and Lamiiflorae, while the monocotyledons are divided into reven superorders, the Alismatiflorae, Ariflorae, Triuridiflorae. Liliiflorae, Zingiberiflorae, Commeliniflorae and Areciflorae. The higher categories are not defined here, but some general features in the classification are mentioned, and the distribution of some attributes is shown in the diagram.  相似文献   

9.
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11.
Act globally     
Michael Gross looks at a report on how carbon emissions could be tackled.  相似文献   

12.
Since Darwin, the diversity of flowers has been attributed to selection by pollinators. Although pollinators commonly act as selective agents on floral traits, determining the extent to which they have influenced angiosperm diversification requires a historical perspective. Here we review recent studies that combine species-level phylogenies with pollinator data and show that pollinator shifts are common, being associated with at least a quarter of documented divergence events. However, shift frequency and directionality vary extensively, owing to variation in intrinsic factors such as floral features and phylogenetic history, as well as extrinsic factors such as interactions with local pollinator assemblages. Despite technical advances, phylogenies remain limited in their power to distinguish among various pollinator-driven evolutionary processes.  相似文献   

13.
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14.
Polyploidy in angiosperms   总被引:11,自引:0,他引:11  
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15.
Incompatibility in angiosperms   总被引:5,自引:0,他引:5  
 Since Darwinian times considerable knowledge has accumulated on the distribution, physiology and genetics of self-incompatibility (SI) in higher plants. In the second half of this century the first attempts were made to identify the biochemical bases of SI. These included thediscovery that cutinase enables pollen tube penetration at the surface* of the stigma in Cruciferae, sorting of segregation pollen S-phenotypes by serological techniques, a lock-and-key model of the SI reaction, the first detection and characterisation of SI proteins and the discovery of the role of the tapetum in the determination of pollen phenotypes in homomorphic sporophytic SI. This pioneering work was followed by a worldwide effort to identify and understand the cellular and molecular processes which lead to the recognition and rejection of SI pollen. The present review article summarizes briefly the current state of knowledge in areas essential for the understanding and exploitation of SI and outlines new information that has become available during recent years. Received: 14 March 1997 / Revision accepted: 10 June 1997  相似文献   

16.
Dichogamy in angiosperms   总被引:1,自引:0,他引:1  
We obtained information on dichogamy and other aspects of the biology of over 4200 species of angiosperms from several hundred published and unpublished sources. We used this information to describe patterns of occurrence of dichogamy and to test specific hypotheses relating dichogamy to other characteristics of plants or their environments. Protandry was more common than protogyny at the intrafloral level, but the reverse was true at the interfloral level. Patterns of dichogamy varied significantly among major taxa, with protogyny more common among monocotyledons and primitive dicotyledons, and protandry expecially common in the Asteridae. Arctic species tended to be less dichogamous and more protogynous than temperate and tropical species. Aquatic and alpine species were especially protogynous. Patterns of dichogamy varied among sexual systems, with gynomonoecious and gynodioecious species especially protandrous, and monoecious species highly protogynous. Autogamous and self-compatible species were disproportionately protogynous. Flowers of intraflorally dichogamous species were slightly larger than those of adichogamous species, owing to the presence of many autogamous species in the latter group. Species with interfloral protogyny bore much smaller flowers than did species with interfloral protandry. Early-blooming species in north-temperate and polar regions were disproportionately protogynous. Sexual structures that abscised, shriveled or moved after completion of their function tended to be presented first, and those that facilitated the other sexual function were presented second. A negative association existed between type of intrafloral and interfloral dichogamy in diclinous species. Most animal-pollinated flowers were protandrous, except beetle-pollinated and refuge and trap blossoms. Wind pollination was markedly associated with protogyny. Vertical inflorescences visited by upwardly-moving vectors were protandrous.  相似文献   

17.
Phylogenetic evidence for the herbaceous origin of angiosperms   总被引:7,自引:0,他引:7  
The ancestral angiosperm is commonly interpreted as an arborescent to shrubby magnolialean with large, multiparted, complex flowers. We examined this hypothesis using a phylogenetic analysis of new and reevaluated characters polarizabled with outgroup comparison. Our cladistic analysis of basal angiosperms placed the nonmagnolialeanChloranthaceae andPiperaceae at the bottom of the tree. We further inferred the probable ancestral states of characters not polarizable with outgroup comparison by examining their distribution among taxa at the base of our cladogram. The sum of ancestral character states suggests that the protoangiosperm was a diminutive, rhizomatous to scrambling perennial herb, with small, simple flowers.  相似文献   

18.
A simple point-charge potential, developed earlier for the calculation of intermolecular forces in molecular-dynamics simulations of liquid water, has been extended to include interactions between water molecules and polar groups of proteins. A complete potential for use in the simulation of protein dynamics in water is reported.  相似文献   

19.
After deceration, celloidinization and hydration, oxidize 10 micron paraffin sections for 15 min in a solution containing 0.3 g KMnO4 and 0.1 ml conc. H2SO4 per 100 ml distilled water. Wash in water and reduce in 5% oxalic acid until the sections are colorless. Wash thoroughly in water and place in 4% iron alum solution for two hours. Wash briefly in water and stain for two hours in phosphotungstic acid hematoxylin. Rinse briefly in 95% ethanol and dehydrate in n-butyl alcohol or absolute ethanol for 4 min with two changes, clear and mount. Glial fibers, myofibrils, red blood cells, etc. are stained blue while astrocyte cell bodies, collagen, etc. are stained red. This stain has proven highly consistent in a wide variety of astrocytic derangements. Despite the intensity of this PTAH modification, false positive staining was not observed.  相似文献   

20.
We need to set priorities for conservation because we cannot do everything, everywhere, at the same time. We determined priority areas for investment in threat abatement actions, in both a cost-effective and spatially and temporally explicit way, for the threatened mammals of the world. Our analysis presents the first fine-resolution prioritization analysis for mammals at a global scale that accounts for the risk of habitat loss, the actions required to abate this risk, the costs of these actions and the likelihood of investment success. We evaluated the likelihood of success of investments using information on the past frequency and duration of legislative effectiveness at a country scale. The establishment of new protected areas was the action receiving the greatest investment, while restoration was never chosen. The resolution of the analysis and the incorporation of likelihood of success made little difference to this result, but affected the spatial location of these investments.  相似文献   

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