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    Detection of metastable electronic states by Penning trap mass spectrometry. Schüssler R X,Bekker H,Braß M,Cakir H,Crespo López-Urrutia J R,Door M,Filianin P,Harman Z,Haverkort M W,Huang W J,Indelicato P,Keitel C H,König C M,Kromer K,Müller M,Novikov Y N,Rischka A,Schweiger C,Sturm S,Ulmer S,Eliseev S,Blaum K Nature State-of-the-art optical clocks achieve precisions of 10 or better using ensembles of atoms in optical lattices or individual ions in radio-frequency traps. Promising candidates for use in atomic clocks are highly charged ions (HCIs) and nuclear transitions, which are largely insensitive to external perturbations and reach wavelengths beyond the optical range that are accessible to frequency combs. However, insufficiently accurate atomic structure calculations hinder the identification of suitable transitions in HCIs. Here we report the observation of a long-lived metastable electronic state in an HCI by measuring the mass difference between the ground and excited states in rhenium, providing a non-destructive, direct determination of an electronic excitation energy. The result is in agreement with advanced calculations. We use the high-precision Penning trap mass spectrometer PENTATRAP to measure the cyclotron frequency ratio of the ground state to the metastable state of the ion with a precision of 10-an improvement by a factor of ten compared with previous measurements. With a lifetime of about 130 days, the potential soft-X-ray frequency reference at 4.96 × 10 hertz (corresponding to a transition energy of 202 electronvolts) has a linewidth of only 5 × 10 hertz and one of the highest electronic quality factors (10) measured experimentally so far. The low uncertainty of our method will enable searches for further soft-X-ray clock transitions in HCIs, which are required for precision studies of fundamental physics. 10.1038/s41586-020-2221-0
    Mass-spectrometry-based draft of the Arabidopsis proteome. Mergner Julia,Frejno Martin,List Markus,Papacek Michael,Chen Xia,Chaudhary Ajeet,Samaras Patroklos,Richter Sandra,Shikata Hiromasa,Messerer Maxim,Lang Daniel,Altmann Stefan,Cyprys Philipp,Zolg Daniel P,Mathieson Toby,Bantscheff Marcus,Hazarika Rashmi R,Schmidt Tobias,Dawid Corinna,Dunkel Andreas,Hofmann Thomas,Sprunck Stefanie,Falter-Braun Pascal,Johannes Frank,Mayer Klaus F X,Jürgens Gerd,Wilhelm Mathias,Baumbach Jan,Grill Erwin,Schneitz Kay,Schwechheimer Claus,Kuster Bernhard Nature Plants are essential for life and are extremely diverse organisms with unique molecular capabilities. Here we present a quantitative atlas of the transcriptomes, proteomes and phosphoproteomes of 30 tissues of the model plant Arabidopsis thaliana. Our analysis provides initial answers to how many genes exist as proteins (more than 18,000), where they are expressed, in which approximate quantities (a dynamic range of more than six orders of magnitude) and to what extent they are phosphorylated (over 43,000 sites). We present examples of how the data may be used, such as to discover proteins that are translated from short open-reading frames, to uncover sequence motifs that are involved in the regulation of protein production, and to identify tissue-specific protein complexes or phosphorylation-mediated signalling events. Interactive access to this resource for the plant community is provided by the ProteomicsDB and ATHENA databases, which include powerful bioinformatics tools to explore and characterize Arabidopsis proteins, their modifications and interactions. 10.1038/s41586-020-2094-2