Classification of Azolla spp., section Azolla     

William J. Zimmerman  Thomas A. Lumpkin  Iwao Watanabe 《Euphytica》1989,43(3):223-232

Summary Azolla accessions (section Azolla) from the germplasm collections of the International Rice Research Institute and Washington State University were fingerprinted and classified by enzyme electrophoresis and leaf trichome morphology. A. filiculoides was enzymatically distinctive and also reliably identified by its prominent one-celled trichomes. Neotropical accessions labelled as A. filiculoides proved to be members of other species. Two groups of isolates were designated A. rubra, but those from Japan were identified as A. filiculoides. The A. rubra of Australia-New Zealand was biochemically unique and possessed less protuberant trichomes than A. filiculoides. A. microphylla, A. mexicana, and A. caroliniana were phenetically similar, but a. microphylla was identifiable from the others in the banding patterns of certain enzymes. A. mexicana and A. caroliniana were closely related enzymatically. The two-celled leaf trichomes of these three species were similar in size and shape.  相似文献   

Untersuchungen zum Einfluß des Matrixpotentials im Boden auf Stammdickenänderungen von Fichten (Picea abies (L.) Karst.)     

Jin-Chen Liu  Karl-Heinz Hberle  Kurt Loris 《植物养料与土壤学杂志》1995,158(3):231-234

Effects of soil water potential on stem radius changes of Norway spruce (Picea abies (L.) Karst.) The stem radius of 2 mature Norway spruce trees and the soil water potential were continuously measured in situ with dendrometers and tensiometers, respectively. In a period without growth and frost events the stem radius and the soil water potentials correlated closely. A young spruce tree grown under controlled conditions changed its radius in response to the soil water supply likewise. The shrinkage of the stem was reversible, even if the soil was very dry (soil water potential ± ? 1000 hPa). An estimate of the soil water potential seems to be possible even beyond ? 1000 hPa by measurements of stem radius changes.  相似文献   

Untersuchungen zur Entwicklung der apomiktischen Fortpflanzungsweise bei Futtergräsern II. Hybrideffekt und Fertilität von Art- und Gattungsbastarden     

Kurt Gröber  Fritz Matzk  Martin Zacharias 《Genetic Resources and Crop Evolution》1976,24(1):349-364

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Zytologische und embryologische Untersuchungen am Nucellus apomiktischer Sippen der Wiesenrispe (Poa pratensis L.)     

Kurt Gröber 《Genetic Resources and Crop Evolution》1986,34(2):147-158

Zusammenfassung Bei apomiktischen Sippen vonPoa pratensis wurden 165 Samenanlagen auf die Anzahl der in ihren Nucelli ausgebildeten Embryosäcke untersucht. Dabei wurden in 87 Nucelli ein, in 60 zwei und in 18 drei Embryosäcke gefunden. Im Einzelfall sind in diesem Stadium apomiktische von sexuellen Embryosäcken nicht zu unterscheiden; es kann aber aus der bekannten hohen Apomixierate bei Zuchtmaterial geschlossen werden, daß es sich dabei fast ausnahmslos um solche aposporen Ursprungs handelt.Die zahlenmäßige Erfassung keimfähiger mono-, bi- und polyembryonaler Karyopsen erfolgt im Keimapparat auf Filterpapier. Die auf diese Weise ermittelte Differenz zu den mittels embryologischer Methoden erfaßten Embryosäcken ist beträchtlich. Von der Anzahl aposporer Initialen je Nucellus über die Anzahl entwickelter Embryosäcke je Nucellus bis zur Ausbildung keimfähiger Embryonen je Karyopse, ist zahlenmäßig eine starke Verminderung festzustellen.In dem befruchtungsfähigen Embryosack bilden, wie zu erwarten, drei Kerne den Eiapparat, zwei die Polkerne und drei die Antipoden. Durch somatische Polyploidisierung erfahren die Antipoden stets eine auffällige Volumenzunahme, und es kann sich durch zusätzliche Teilungen auch ihre Anzahl erhöhen.

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Cytological and embryological studies in nucelli of apomictic specimens ofPoa pratensis L.

Summary In a total of 165 analysed nucelli of apomictic specimens ofPoa pratensis 87 contain only one embryo-sac, 60 two embryo-sacs and 18 three ones. In no case aposporous embryo-sacs could be distinguished from meiotic ones. However, from the high apomeiotic rate in breeding material the conclusion can be drawn that the majority of them are of aposporous origin.The numerical evaluation of the germinating capacity of mono-, bi- and polyembryonic caryopses was performed in a germinating apparatus. There are considerable differences between the values determined in this way and those ascertained by embryological methods. It was found that during the developmental pathway from the aposporous initial to the mature, full-grown embryo sequentially the number of embryo-sacs per nucellus and the number of embryos capable to germinate per caryopsis are diminished.As expected, in the mature, fertile embryo-sac three nuclei form the egg-apparatus, two ones the pole nuclei and three ones the antipodals. By somatic polyploidization the antipodals always undergo a considerable increase in volume, and in few cases by additional divisions the number of antipodals may be increased also.

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(Poa pratensis L.)

Poa pratensis 165 , , . 87 , 60 — 18 . , , ; , , , , . -, - . , , , , . , , , . , , , . , , , .

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Endangered bird species: habitat manipulation methods     

Zimmerman DR 《Science (New York, N.Y.)》1976,192(4242):876-878

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Visualization and functional analysis of RNA-dependent RNA polymerase lattices     

Lyle JM  Bullitt E  Bienz K  Kirkegaard K 《Science (New York, N.Y.)》2002,296(5576):2218-2222

Positive-strand RNA viruses such as poliovirus replicate their genomes on intracellular membranes of their eukaryotic hosts. Electron microscopy has revealed that purified poliovirus RNA-dependent RNA polymerase forms planar and tubular oligomeric arrays. The structural integrity of these arrays correlates with cooperative RNA binding and RNA elongation and is sensitive to mutations that disrupt intermolecular contacts predicted by the polymerase structure. Membranous vesicles isolated from poliovirus-infected cells contain structures consistent with the presence of two-dimensional polymerase arrays on their surfaces during infection. Therefore, host cytoplasmic membranes may function as physical foundations for two-dimensional polymerase arrays, conferring the advantages of surface catalysis to viral RNA replication.  相似文献   

New Permian Insects Discovered in Kansas and Oklahoma     

Tasch P  Zimmerman JR 《Science (New York, N.Y.)》1959,130(3389):1656-1657

In addition to the viviparous fish Mollienesia formosa, two other species of poeciliids have recently been found to produce only female offspring. The young of these females, however, unlike those of M. formosa, inherit characteristics from any one of the several species of males used in experimental matings.  相似文献   

Thunderstorms: an important mechanism in the transport of air pollutants   总被引：3，自引：0，他引：3  

Dickerson RR  Huffman GJ  Luke WT  Nunnermacker LJ  Pickering KE  Leslie AC  Lindsey CG  Slinn WG  Kelly TJ  Daum PH  Delany AC  Greenberg JP  Zimmerman PR  Boatman JF  Ray JD  Stedman DH 《Science (New York, N.Y.)》1987,235(4787):460-465

Acid deposition and photochemical smog are urban air pollution problems, and they remain localized as long as the sulfur, nitrogen, and hydrocarbon pollutants are confined to the lower troposphere (below about 1-kilometer altitude) where they are short-lived. If, however, the contaminants are rapidly transported to the upper troposphere, then their atmospheric residence times grow and their range of influence expands dramatically. Although this vertical transport ameliorates some of the effects of acid rain by diluting atmospheric acids, it exacerbates global tropospheric ozone production by redistributing the necessary nitrogen catalysts. Results of recent computer simulations suggest that thunderstorms are one means of rapid vertical transport. To test this hypothesis, several research aircraft near a midwestern thunderstrom measured carbon monoxide, hydrocarbons, ozone, and reactive nitrogen compounds. Their concentrations were much greater in the outflow region of the storm, up to 11 kilometers in altitude, than in surrounding air. Trace gas measurements can thus be used to track the motion of air in and around a cloud. Thunderstorms may transform local air pollution problems into regional or global atmospheric chemistry problems.  相似文献   

Action spectra for phase shifts of a circadian rhythm in Drosophila   总被引：9，自引：0，他引：9  

K D Frank  W F Zimmerman 《Science (New York, N.Y.)》1969,163(868):688-689

Action spectra were determined for lightinduced phase shifts of the circadian rhythm of adult emergence in Drosophila pseudoobscura. The action spectra for advance and delay phase shifts are similar; the most effective wavelengths are in the blue region, with a sharp cutoff above 500 nanometers. This similarity suggests that the same photoreceptive pigment mediates both advance and delay phase shifts.  相似文献   

Complement-induced platelet protein alterations   总被引：1，自引：0，他引：1  

T S Zimmerman  H J Müller-Eberhard 《Science (New York, N.Y.)》1973,180(91):1183-1185

Polypeptides of high molecular weight are deleted from the sedimentable fraction of platelets subjected, while intact, to complement action. These polypeptides, distinct from the previously described thrombin-sensitive protein of this fraction, also diminish after platelets are exposed to thrombin. They may be of importance in the molecular events underlying complement-triggered changes in platelet function.  相似文献