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531.
532.
Mentzelia hualapaiensis, a new species of Mentzelia sect. Bartonia, is described from the Grand Canyon region of Arizona. The new species is closely related to M. puberula, which is found west of M. hualapaiensis along the Colorado River, and to M. oreophila, M. polita, and M. tiehmii. It shares with these species a suffrutescent shoot system characterized by a subterranean, branching caudex, multiple annual
branches, and similar leaves that have shallowly lobed or toothed to entire laminas. The flowers of M. hualapaiensis differ from those of its closest relatives in having cream-white, linear to narrowly spatulate petals and staminodes, characteristics
that are convergent with those of the flowers of the Chihuahuan Desert species M. humilis. 相似文献
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The detectability of stored growth at various elongation rates(IAA- and acid- induced) was investigated in 5-mm wheat coleoptilesegments. After 20 min turgor reduction by 0.15 M or 0.20 Mmannitol, the detectability of stored growth depended on theelongation rate before turgor reduction. A hypothesis was proposedthat the amount of stored growth is limited. Depending on theelongation rate, this then appears as complete or partial compensationof the growth lost during turgor reduction. The limit for fullcompensation was about 300 µm/hr?segment. At elongationrates of > 600 µm/hr?segment, no stored growth couldbe detected. The elongation of the wheat coleoptile sectionsat low and high elongation rates is assumed to be limited bydifferent rate-determining steps. (Received November 22, 1977; ) 相似文献
537.
M Chiquet N Vrucini?-Filipi S Schenk K Beck R Chiquet-Ehrismann 《European journal of biochemistry》1991,199(2):379-388
The extracellular-matrix glycoprotein, tenascin, consists of disulfide-linked subunits of 190, 200 and 230 kDa (the three splicing variants reported in chicken) and usually exists as a six-armed structure under the electron microscope. We used monoclonal antibodies to isolate and characterize different splicing variants and proteolytic fragments obtained from the native protein. Purified monomeric tenascin has a native molecular mass of 216 kDa and is structured as single arms. Tenascin fragments obtained by pepsin digestion bind to monoclonal antibody (mAb) TnM1 which is directed against epidermal-growth-factor-like repeats in the N-terminal half of all subunits. These fragments represent the thin proximal part of the tenascin arms and they are still partially linked to dimers and trimers via disulfide bridges. Using mAb Tn68, that reacts with a fibronectin-type-III repeat towards the C-terminus, a tenascin fragment, generated by treatment with pronase, can be isolated. Ultrastructurally, this fragment looks like the thicker distal part of the tenascin arms. Only the 230-kDa variant of tenascin gives rise to this distal fragment after cleavage within the alternatively spliced fibronectin-type-III repeats. Native tenascin and all fragments containing the distal part of its arms bind to heparin-agarose, whereas the proximal fragments do not. Oligomeric and monomeric tenascin inhibit fibronectin-mediated fibroblast spreading with comparable efficiency when added to the culture medium, while the proximal fragment has no effect. The distal fragment as well as reduced and alkylated tenascin are active in this assay, but only at higher molar concentrations when compared to the native protein. 相似文献
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U B Gebhart T L Maier S Stevanovi? M G Bayer H E Schenk 《Protein expression and purification》1992,3(3):228-235
The ferredoxin:NADP+ oxidoreductase of the protist Cyanophora paradoxa, as a descendant of a former symbiotic consortium, an important model organism in view of the Endosymbiosis Theory, is the first enzyme purified from a formerly original endocytobiont (cyanelle) that is found to be encoded in the nucleus of the host. This cyanoplast enzyme was isolated by FPLC (19% yield) and characterized with respect to the uv-vis spectrum, pH optimum (pH 9), molecular mass of 34 kDa, and an N-terminal amino acid sequence (24 residues). The enzyme shows, as known from other organisms, molecular heterogeneity. The N-terminus of a further ferredoxin:NADP+ oxidoreductase polypeptide represents a shorter sequence missing the first four amino acids of the mature enzyme. 相似文献
540.
Zusammenfassung Der Begriff CO2-Kompensationspunkt wird im Vergleich zum Begriff Licht-Kompensationspunkt an Hand von Meßergebnissen erläutert. Die Lage des CO2-Kompensationspunktes ist von der Temperatur abhängig derart, daß sich bei höherer Temperatur das Gleichgewicht zwischen CO2-Aufnahme und-abgabe im belichteten Gewebe bei einem höheren CO2-Partialdruck der Umgebung einstellt. Die Temperaturkoeffizienten für die Dunkelatmung, die apparente und die gesamte Photosynthese werden in Form vonQ
10-Werten wiedergegeben. Da diese Werte bei der photosynthetischen CO2 Verarbeitung wesentlich kleiner sind wie die bei photochemischen und chemischen Reaktionen beobachteten Temperaturkoeffizienten, wurde vermutet, daß der mit zunehmender Temperatur beobachtete steile Abfall der apparenten Photosynthese sowie die Temperaturabhängigkeit der Gesamtphotosynthese in Form einer Optimumkurve auf eine temperaturabhängige Veränderung der Reaktionsbedingungen zurückzuführen ist. Solche temperaturbedingten Veränderungen sind in bezug auf das CO2-Diffusionsgefälle zwischen der die Pflanze umgebenden Luft und den Reaktionsorten für die Bindung und photosynthetische Verarbeitung des Kohlendioxyds im Gewebe gegeben, so daß anzunehmen ist, daß die beobachteten Temperaturwirkungen in erster Linie auf temperaturbedingte Veränderungen physikalisch-physiologischer Größen bei dem vor der eigentlichen photochemischen und chemischen CO2-Verarbeitung stattfindenden Diffusionsvorgang zurückzuführen sind.Mit 8 Textabbildungen.Herrn Prof. Dr.O. Renner zum 70. Geburtstag gewidmet. 相似文献