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排序方式: 共有260条查询结果,搜索用时 15 毫秒
1.
Tryptophan, tryptamine, or indolepyruvic acid were applied to 2 systems: a bacterial (pea stem sections containing the epiphytic bacteria) and a plant system (pea stem sections under sterile conditions). In the plant system, the production of indoleacetic acid and indoleethanol (tryptophol) from each applied indole derivative is clearly reduced by the aldehyde reagents bisulfite and dimedon, respectively. Indoleacetaldehyde is chromatographically detected after alkaline liberation from its bisulfite addition product. In the bacterial system, the production of indoleacetic acid and indoleethanol is likewise reduced by bisulfite and dimedon. However, after tryptophan or tryptamine application, we could not detect indoleacetaldehyde in the described way. In one case only, namely tryptamine application to the bacterial system, indoleethanol production (contrary to indoleacetic acid production) is scarcely reduced by the aldehyde reagents. This indicates a bacterial pathway tryptamine → indoleethanol which bypasses indoleacetaldehyde. 相似文献
2.
Summary An analysis was made of the effects of different sampling and extraction techniques on the amounts and pattern of monoterpenoids isolated from needles of Norway spruce. The following isolation and analysis procedure was finally adopted: liquid nitrogen-cooled needles were pulverized by a microdismembrator, extracted with pentane overnight at 2°–3°C and concentrated to a volume not less than 3 ml/g fresh weight on a Vigreux column. The crude extract was injected splitless (with solvent split) onto a cold programmed temperature vaporized (PTV) precolumn of a gas chromatograph and the vaporizable compounds heated to a capillary column. This method was tested for production of artefacts and quantitative extraction and applied to needles of eleven 80-year-old spruce trees. 相似文献
3.
4.
Mohammadjavad Haghighatnia Antonin Machac Roswitha Schmickl Clément Lafon Placette 《Biological reviews of the Cambridge Philosophical Society》2023,98(6):1928-1944
Sexual selection is considered one of the key processes that contribute to the emergence of new species. While the connection between sexual selection and speciation has been supported by comparative studies, the mechanisms that mediate this connection remain unresolved, especially in plants. Similarly, it is not clear how speciation processes within plant populations translate into large-scale speciation dynamics. Here, we review the mechanisms through which sexual selection, pollination, and mate choice unfold and interact, and how they may ultimately produce reproductive isolation in plants. We also overview reproductive strategies that might influence sexual selection in plants and illustrate how functional traits might connect speciation at the population level (population differentiation, evolution of reproductive barriers; i.e. microevolution) with evolution above the species level (macroevolution). We also identify outstanding questions in the field, and suitable data and tools for their resolution. Altogether, this effort motivates further research focused on plants, which might potentially broaden our general understanding of speciation by sexual selection, a major concept in evolutionary biology. 相似文献
5.
The influence of nicotianamine (NA) on formation and elongation of adventitious roots in hypocotyls of de-rooted NA-less mutant seedlings of Lycopersicon esculentum Mill, was examined in relation to the iron supply [ferric N-N'-ethylenediaminedi-(2-hydroxyphenylacetate) (FEDDHA), ferric ethylenediaminetetracetate (FeEDTA), ferric N-(2-hydroxyethyl)-ethylenediaminetriacetate (FeHEDTA, Fe-citrate and FeCl3 ] in the nutrient solution. The initiation of root primordia in hypocotyl cuttings was independent of NA and occurred with about the same frequency in both, mutant and wild-type. In the mutant the development of primordia to adventitious roots was blocked at all iron sources used, except FeEDTA. Addition of NA (5x 10−6 to 2 × 10−5 M ) to the rooting medium resulted in a fast growth of adventitious roots in mutant cuttings with all iron sources tested. Rooting of wild-type cuttings was independent from NA application and iron sources. We suppose that NA is involved in the intracellular transport of iron. Its function is possibly linked with chelation of ferrous iron in the cell. 相似文献
6.
Summary The intratesticular excurrent duct system of the bull is composed of rete testis, tubuli recti, and the terminal segment of the seminiferous tubules. Each terminal segment is surrounded by a vascular plexus and may be subdivided into a transitional region, middle portion, and terminal plug. The modified supporting cells of the middle portion and the terminal plug no longer display the typical Sertoli-Sertoli junctions seen in the transitional region and the seminiferous tubule proper. In the region of the terminal plug a distinct central lumen is generally not observed: spermatozoa and tubular fluid must pass through an intricate system of communicating clefts between the apices of the closely attached modified supporting cells. Vacuoles in the supranuclear region of the cells in the middle portion indicate strong transepithelial fluid transport. In analogy to the epithelium of rete testis and tubuli recti, the supporting cells of the terminal segment are capable of phagocytosing spermatozoa. The vascular plexus investing the terminal segment serves a dual purpose: it is a regulatory device for fluid and sperm transport, as well as an area of increased diapedesis for white blood cells.Supported by a grant from the Deutsche Forschungsgemeinschaft 相似文献
7.
Roswitha Wiltschko 《Journal of Ornithology》1981,122(1):1-22
Zusammenfassung Die vorliegende Arbeit versucht, die Sonnenorientierung der Vögel in ihrer Funktionsweise, ontogenetischen Entwicklung und biologischen Bedeutung nach dem heutigen Wissensstand darzustellen. Theoretisch kann die Sonne zur Bestimmung der Heimrichtung ( navigation), zum Aufsuchen einer als Kompaßrichtung bekannten Richtung und zum Einhalten der Richtung benutzt werden. Die meisten vorliegenden Befunde sprechen gegen eine Rolle der Sonne bei der Bestimmung der Heimrichtung nach Verfrachtung; die Funktion der Sonne als Sonnenkompaß und beim Richtungseinhalten ist dagegen durch zahlreiche Versuche bei verschiedenen Vogelarten gut belegt.Beim Aufsuchen einer Richtung mit dem Sonnenkompaß verrechnet der Vogel die Bewegung der Sonne auf ihrer scheinbaren Bahn, d. h. er schlägt einen tageszeitlich variablen Winkel zur Sonne ein, um in eine konstante Richtung zu fliegen. Dieser Winkel hängt allein von der inneren Uhr ab. Dabei scheint der Vogel im allgemeinen zu berücksichtigen, daß die Azimutwinkelgeschwindigkeit der Sonne gegen Mittag erheblich größer ist als in den frühen Vormittags- und späten Nachmittagsstunden.Untersuchungen bei Tauben ergaben, daß der Sonnenkompaß ein erlernter Orientierungsmechanismus ist: Sonnenazimut, Zeit und geographische Richtung werden aufgrund von Erfahrung miteinander in Beziehung gesetzt. Dabei muß die junge Taube die Sonne zu verschiedenen Tageszeiten beobachten, um den Sonnenkompaß während des ganzen Tages benutzen zu können. Der Zeitpunkt, zu dem der Sonnenkompaß gelernt wird, hängt stark von der Flugerfahrung der Tauben ab; er scheint sich zu entwickeln, sobald die Notwendigkeit, sich zu orientieren, auftritt, was normalerweise etwa gegen Ende des 3. Lebensmonats der Fall sein dürfte. Die Grundlagen und näheren Umstände des Lernprozesses sind noch weitgehend unbekannt.Versuche mit jungen Tauben sprechen dafür, daß der Sonnenkompaß bei der Entwicklung der Navigationsfähigkeit keine Rolle spielt; er scheint quasi nachträglich in das fertige Navigationssystem eingebaut zu werden. Dann aber stellt der Sonnenkompaß beim Heimfinden das bevorzugt benutzte Kompaßsystem dar, solange die Sonne zu sehen ist. Bei bedecktem Himmel kann er allerdings durch ein gleich leistungsfähiges nicht-visuelles System ersetzt werden.Bei tagziehenden jungen Zugvögeln — finnischen Staren — ließ sich eine Orientierung nach dem Sonnenkompaß noch nicht während des ersten Herbstzuges, sondern erst während des folgenden Frühjahrszuges nachweisen; allerdings ist unklar, inwieweit diese an handaufgezogenen Vögeln gewonnenen Befunde die natürlichen Verhältnisse widerspiegeln. Eine realistische Abschätzung der Bedeutung des Sonnenkompaß bei der Zugorientierung ist heute noch nicht möglich; theoretische überlegungen und die wenigen vorliegenden Befunde scheinen jedoch gegen eine Rolle des Sonnenkompaß als Referenzsystem für die angeborene Zugrichtung zu sprechen.
The sun orientation of birds
Summary In the present paper (part I: J. Orn. 121: 121–143, 1980), the sun orientation of birds, its way of functioning, ontogenetic development, and biological significance are described in the light of current experimental evidence. Theoretically, the sun can be used to determine which compass direction is the home direction ( true navigation), to set a compass course, and to maintain a given direction during flight. Most of the available evidence speaks against the sun's being used for determining the home direction after displacement, whereas many findings in several species of birds demonstrate use of the sun as a sun compass and for maintaining directions.Using the sun compass to go in a constant direction, the birds compensate for the sun's apparent movement, i. e. they fly at angles to the sun's azimuth direction which vary according to the time of day. The magnitude of these angles seems to depend on the birds' internal clock only, and the birds apparently consider the different rates of change of the sun's azimuth during the day (greater around noon than in early morning or late afternoon).Experiments with young homing pigeons show that the sun compass is not a completely innate orientation mechanism, but that the relation between sun azimuth, time and geographic direction is learned. A young pigeon must experience the sun at different hours of the day to establish a sun compass for the entire day. The age at which the sun compass is learned strongly depends on the bird's flying experience. The sun compass seems to be developed as soon as the bird encountered the necessity of orienting, which normally will be about the end of its third month. The details of the learning process are not yet known.The sun does not seem to be necessary for the development of the ability to navigate; in fact, some findings with young pigeons seem to indicate that the navigational system is already developed before the sun compass is added to it. Afterwards, however, the sun compass is used preferentially whenever the sun is visible. Under overcast skies, it is replaced by an equally effective non-visual system.In day-migrating birds — young Finnish starlings — sun compass orientation could not be demonstrated during the first autumn migration period, but the starlings were shown to use it during the following spring period. It is not clear, though, whether these data from handraised birds reflect the natural situation correctly. The available evidence does not yet allow a realistic estimate of the significance of the sun compass for orientation during migration; theoretical considerations and the few present data, however, make it appear improbable that the sun compass acts as a reference system for the innate migratory direction.相似文献
8.
Stefanie Wagner Frédéric Lagane Andaine Seguin‐Orlando Mikkel Schubert Thibault Leroy Erwan Guichoux Emilie Chancerel Inger Bech‐Hebelstrup Vincent Bernard Cyrille Billard Yves Billaud Matthias Bolliger Christophe Croutsch Katarina Čufar Frédérique Eynaud Karl Uwe Heussner Joachim Köninger Fabien Langenegger Frédéric Leroy Christine Lima Nicoletta Martinelli Garry Momber André Billamboz Oliver Nelle Antoni Palomo Raquel Piqué Marianne Ramstein Roswitha Schweichel Harald Stäuble Willy Tegel Xavier Terradas Florence Verdin Christophe Plomion Antoine Kremer Ludovic Orlando 《Molecular ecology》2018,27(5):1138-1154
Reconstructing the colonization and demographic dynamics that gave rise to extant forests is essential to forecasts of forest responses to environmental changes. Classical approaches to map how population of trees changed through space and time largely rely on pollen distribution patterns, with only a limited number of studies exploiting DNA molecules preserved in wooden tree archaeological and subfossil remains. Here, we advance such analyses by applying high‐throughput (HTS) DNA sequencing to wood archaeological and subfossil material for the first time, using a comprehensive sample of 167 European white oak waterlogged remains spanning a large temporal (from 550 to 9,800 years) and geographical range across Europe. The successful characterization of the endogenous DNA and exogenous microbial DNA of 140 (~83%) samples helped the identification of environmental conditions favouring long‐term DNA preservation in wood remains, and started to unveil the first trends in the DNA decay process in wood material. Additionally, the maternally inherited chloroplast haplotypes of 21 samples from three periods of forest human‐induced use (Neolithic, Bronze Age and Middle Ages) were found to be consistent with those of modern populations growing in the same geographic areas. Our work paves the way for further studies aiming at using ancient DNA preserved in wood to reconstruct the micro‐evolutionary response of trees to climate change and human forest management. 相似文献
9.
Purpose
The occurrence of brushite stones has increased during recent years. However, the pathogenic factors driving the development of brushite stones remain unclear.Methods
Twenty-eight brushite stone formers and 28 age-, sex- and BMI-matched healthy individuals were enrolled in this case-control study. Anthropometric, clinical, 24 h urinary parameters and dietary intake from 7-day weighed food records were assessed.Results
Pure brushite stones were present in 46% of patients, while calcium oxalate was the major secondary stone component. Urinary pH and oxalate excretion were significantly higher, whereas urinary citrate was lower in patients as compared to healthy controls. Despite lower dietary intake, urinary calcium excretion was significantly higher in brushite stone patients. Binary logistic regression analysis revealed pH>6.50 (OR 7.296; p = 0.035), calcium>6.40 mmol/24 h (OR 25.213; p = 0.001) and citrate excretion <2.600 mmol/24 h (OR 15.352; p = 0.005) as urinary risk factors for brushite stone formation. A total of 56% of patients exhibited distal renal tubular acidosis (dRTA). Urinary pH, calcium and citrate excretion did not significantly differ between patients with or without dRTA.Conclusions
Hypercalciuria, a diminished citrate excretion and an elevated pH turned out to be the major urinary determinants of brushite stone formation. Interestingly, urinary phosphate was not associated with urolithiasis. The increased urinary oxalate excretion, possibly due to decreased calcium intake, promotes the risk of mixed stone formation with calcium oxalate. Neither dietary factors nor dRTA can account as cause for hypercalciuria, higher urinary pH and diminished citrate excretion. Further research is needed to define the role of dRTA in brushite stone formation and to evaluate the hypothesis of an acquired acidification defect. 相似文献10.