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51.
The chloroplast is the hallmark organelle of plants. It performs photosynthesis and is therefore required for photoautotrophic
plant growth. The chloroplast is the most prominent member of a family of related organelles termed plastids which are ubiquitous
in plant cells. Biogenesis of the chloroplast from undifferentiated proplastids is induced by light. The generally accepted
endosymbiont hypothesis states that chloroplasts have arisen from an internalized cyanobacterial ancestor. Although chloroplasts
have maintained remnants of the ancestral genome (plastome), the vast majority of the genes encoding chloroplast proteins
have been transferred to the nucleus. This poses two major challenges to the plant cell during chloroplast biogenesis: First,
light and developmental signals must be interpreted to coordinately express genetic information contained in two distinct
compartments. This is to ensure supply and stoichiometry of abundant chloroplast components. Second, developing chloroplasts
must efficiently import nuclear encoded and cytosolically synthesized proteins. A subset of proteins, including such encoded
by the plastome, must further be sorted to the thylakoid compartments for assembly into the photosynthetic apparatus.
Received 1 September 2000; received after revision 27 October 2000; accepted 1 November 2000 相似文献
52.
Rb targets histone H3 methylation and HP1 to promoters 总被引:78,自引:0,他引:78
Nielsen SJ Schneider R Bauer UM Bannister AJ Morrison A O'Carroll D Firestein R Cleary M Jenuwein T Herrera RE Kouzarides T 《Nature》2001,412(6846):561-565
53.
54.
Summary
3H-serine does not label retinal neurons selectively when injected intraocularly in rabbits, as would have been expected if it had been converted to neutrotransmitter glycine. The reason is unknown, but one possibility is that the conversion was blocked during the conditions of the experiment.This work was supported by the Swedish Medical Research Council (project No. 04X-2321) and the Faculty of Medicine, University of Lund. 相似文献
55.
Curro NJ Caldwell T Bauer ED Morales LA Graf MJ Bang Y Balatsky AV Thompson JD Sarrao JL 《Nature》2005,434(7033):622-625
In the Bardeen-Cooper-Schrieffer theory of superconductivity, electrons form (Cooper) pairs through an interaction mediated by vibrations in the underlying crystal structure. Like lattice vibrations, antiferromagnetic fluctuations can also produce an attractive interaction creating Cooper pairs, though with spin and angular momentum properties different from those of conventional superconductors. Such interactions have been implicated for two disparate classes of materials--the copper oxides and a set of Ce- and U-based compounds. But because their transition temperatures differ by nearly two orders of magnitude, this raises the question of whether a common pairing mechanism applies. PuCoGa5 has a transition temperature intermediate between those classes and therefore may bridge these extremes. Here we report measurements of the nuclear spin-lattice relaxation rate and Knight shift in PuCoGa5, which demonstrate that it is an unconventional superconductor with properties as expected for antiferromagnetically mediated superconductivity. Scaling of the relaxation rates among all of these materials (a feature not exhibited by their Knight shifts) establishes antiferromagnetic fluctuations as a likely mechanism for their unconventional superconductivity and suggests that related classes of exotic superconductors may yet be discovered. 相似文献
56.
Israël G Szopa C Raulin F Cabane M Niemann HB Atreya SK Bauer SJ Brun JF Chassefière E Coll P Condé E Coscia D Hauchecorne A Millian P Nguyen MJ Owen T Riedler W Samuelson RE Siguier JM Steller M Sternberg R Vidal-Madjar C 《Nature》2005,438(7069):796-799
Aerosols in Titan's atmosphere play an important role in determining its thermal structure. They also serve as sinks for organic vapours and can act as condensation nuclei for the formation of clouds, where the condensation efficiency will depend on the chemical composition of the aerosols. So far, however, no direct information has been available on the chemical composition of these particles. Here we report an in situ chemical analysis of Titan's aerosols by pyrolysis at 600 degrees C. Ammonia (NH3) and hydrogen cyanide (HCN) have been identified as the main pyrolysis products. This clearly shows that the aerosol particles include a solid organic refractory core. NH3 and HCN are gaseous chemical fingerprints of the complex organics that constitute this core, and their presence demonstrates that carbon and nitrogen are in the aerosols. 相似文献
57.
Rohwer T Hellmann S Wiesenmayer M Sohrt C Stange A Slomski B Carr A Liu Y Avila LM Kalläne M Mathias S Kipp L Rossnagel K Bauer M 《Nature》2011,471(7339):490-493
Intense femtosecond (10(-15)?s) light pulses can be used to transform electronic, magnetic and structural order in condensed-matter systems on timescales of electronic and atomic motion. This technique is particularly useful in the study and in the control of materials whose physical properties are governed by the interactions between multiple degrees of freedom. Time- and angle-resolved photoemission spectroscopy is in this context a direct and comprehensive, energy- and momentum-selective probe of the ultrafast processes that couple to the electronic degrees of freedom. Previously, the capability of such studies to access electron momentum space away from zero momentum was, however, restricted owing to limitations of the available probing photon energy. Here, using femtosecond extreme-ultraviolet pulses delivered by a high-harmonic-generation source, we use time- and angle-resolved photoemission spectroscopy to measure the photoinduced vaporization of a charge-ordered state in the potential excitonic insulator 1T-TiSe(2 )(refs 12, 13). By way of stroboscopic imaging of electronic band dispersions at large momentum, in the vicinity of the edge of the first Brillouin zone, we reveal that the collapse of atomic-scale periodic long-range order happens on a timescale as short as 20?femtoseconds. The surprisingly fast response of the system is assigned to screening by the transient generation of free charge carriers. Similar screening scenarios are likely to be relevant in other photoinduced solid-state transitions and may generally determine the response times. Moreover, as electron states with large momenta govern fundamental electronic properties in condensed matter systems, we anticipate that the experimental advance represented by the present study will be useful to study the ultrafast dynamics and microscopic mechanisms of electronic phenomena in a wide range of materials. 相似文献
58.
Benazzi S Douka K Fornai C Bauer CC Kullmer O Svoboda J Pap I Mallegni F Bayle P Coquerelle M Condemi S Ronchitelli A Harvati K Weber GW 《Nature》2011,479(7374):525-528
The appearance of anatomically modern humans in Europe and the nature of the transition from the Middle to Upper Palaeolithic are matters of intense debate. Most researchers accept that before the arrival of anatomically modern humans, Neanderthals had adopted several 'transitional' technocomplexes. Two of these, the Uluzzian of southern Europe and the Chatelperronian of western Europe, are key to current interpretations regarding the timing of arrival of anatomically modern humans in the region and their potential interaction with Neanderthal populations. They are also central to current debates regarding the cognitive abilities of Neanderthals and the reasons behind their extinction. However, the actual fossil evidence associated with these assemblages is scant and fragmentary, and recent work has questioned the attribution of the Chatelperronian to Neanderthals on the basis of taphonomic mixing and lithic analysis. Here we reanalyse the deciduous molars from the Grotta del Cavallo (southern Italy), associated with the Uluzzian and originally classified as Neanderthal. Using two independent morphometric methods based on microtomographic data, we show that the Cavallo specimens can be attributed to anatomically modern humans. The secure context of the teeth provides crucial evidence that the makers of the Uluzzian technocomplex were therefore not Neanderthals. In addition, new chronometric data for the Uluzzian layers of Grotta del Cavallo obtained from associated shell beads and included within a Bayesian age model show that the teeth must date to ~45,000-43,000 calendar years before present. The Cavallo human remains are therefore the oldest known European anatomically modern humans, confirming a rapid dispersal of modern humans across the continent before the Aurignacian and the disappearance of Neanderthals. 相似文献
59.
Cruikshank DP Dalton JB Dalle Ore CM Bauer J Stephan K Filacchione G Hendrix AR Hansen CJ Coradini A Cerroni P Tosi F Capaccioni F Jaumann R Buratti BJ Clark RN Brown RH Nelson RM McCord TB Baines KH Nicholson PD Sotin C Meyer AW Bellucci G Combes M Bibring JP Langevin Y Sicardy B Matson DL Formisano V Drossart P Mennella V 《Nature》2007,448(7149):54-56
Hyperion, Saturn's eighth largest icy satellite, is a body of irregular shape in a state of chaotic rotation. The surface is segregated into two distinct units. A spatially dominant high-albedo unit having the strong signature of H2O ice contrasts with a unit that is about a factor of four lower in albedo and is found mostly in the bottoms of cup-like craters. Here we report observations of Hyperion's surface in the ultraviolet and near-infrared spectral regions with two optical remote sensing instruments on the Cassini spacecraft at closest approach during a fly-by on 25-26 September 2005. The close fly-by afforded us the opportunity to obtain separate reflectance spectra of the high- and low-albedo surface components. The low-albedo material has spectral similarities and compositional signatures that link it with the surface of Phoebe and a hemisphere-wide superficial coating on Iapetus. 相似文献
60.
L. Beneš S. Štolc V. Bauer M. Tichý 《Cellular and molecular life sciences : CMLS》1982,38(11):1348-1349
Summary The influence of spatial configuration on intensity, onset, and duration of anesthetic effect has been observed in some carbanilate local anesthetics of fixed conformation. Synthesis of the carbanilates is described. 相似文献