M. C. Fujiwara

Production and detection of cold antihydrogen atoms.

A theoretical underpinning of the standard model of fundamental particles and interactions is CPT invariance, which requires that the laws of physics be invariant under the combined discrete operations of charge conjugation, parity and time reversal. Antimatter, the existence of which was predicted by Dirac, can be used to test the CPT theorem—experimental investigations involving comparisons of particles with antiparticles are numerous. Cold atoms and anti-atoms, such as hydrogen and antihydrogen, could form the basis of a new precise test, as CPT invariance implies that they must have the same spectrum. Observations of antihydrogen in small quantities and at high energies have been reported at the European Organization for Nuclear Research (CERN) and at Fermilab, but these experiments were not suited to precision comparison measurements. Here we demonstrate the production of antihydrogen atoms at very low energy by mixing trapped antiprotons and positrons in a cryogenic environment. The neutral anti-atoms have been detected directly when they escape the trap and annihilate, producing a characteristic signature in an imaging particle detector.

Confinement of antihydrogen for 1,000 seconds

Antihydrogen has been created, trapped and stored for 1,000 s. The improved holding time means that we now have access to the ground state of antimatter—long enough to test whether matter and antimatter obey the same physical laws.

Three new nuclear genes, sigD, sigE and sigF, encoding putative plastid RNA polymerase σ factors in Arabidopsis thaliana

Three new nuclear genes (sigD, sigE and sigF) of Arabidopsis thaliana, encoding putative plastid RNA polymerase σ factors, were identified and analyzed. Phylogenetic analysis revealed that higher plant σ factors fell into at least four distinct subgroups within a diverse protein family. In addition, Arabidopsis sig genes contained conserved chromosomal intron sites, indicating that these genes arose by DNA duplication events during plant evolution. Transcript analyses revealed two alternatively spliced transcripts generated from the sigD region, one of which is predicted to encode a σ protein lacking the carboxy‐terminal regions 3 and 4. Finally, the amino‐terminal sequence of the sigF gene product was shown to function as a plastid‐targeting signal using green fluorescent protein fusions.

Resonant quantum transitions in trapped antihydrogen atoms

The hydrogen atom is one of the most important and influential model systems in modern physics. Attempts to understand its spectrum are inextricably linked to the early history and development of quantum mechanics. The hydrogen atom’s stature lies in its simplicity and in the accuracy with which its spectrum can be measured and compared to theory. Today its spectrum remains a valuable tool for determining the values of fundamental constants and for challenging the limits of modern physics, including the validity of quantum electrodynamics and—by comparison with measurements on its antimatter counterpart, antihydrogen—the validity of CPT (charge conjugation, parity and time reversal) symmetry. Here we report spectroscopy of a pure antimatter atom, demonstrating resonant quantum transitions in antihydrogen. We have manipulated the internal spin state of antihydrogen atoms so as to induce magnetic resonance transitions between hyperfine levels of the positronic ground state. We used resonant microwave radiation to flip the spin of the positron in antihydrogen atoms that were magnetically trapped in the ALPHA apparatus. The spin flip causes trapped anti-atoms to be ejected from the trap. We look for evidence of resonant interaction by comparing the survival rate of trapped atoms irradiated with microwaves on-resonance to that of atoms subjected to microwaves that are off-resonance. In one variant of the experiment, we detect 23 atoms that survive in 110 trapping attempts with microwaves off-resonance (0.21 per attempt), and only two atoms that survive in 103 attempts with microwaves on-resonance (0.02 per attempt). We also describe the direct detection of the annihilation of antihydrogen atoms ejected by the microwaves.

The Aspergillus nidulans genes chsA and chsD encode chitin synthases which have redundant functions in conidia formation.

We previously isolated three chitin synthase genes (chsA, chsB, andchsC) fromAspergillus nidulans. In the present work, we describe the isolation and characterization of another chitin synthase gene, namedchsD, fromA. nidulans. Its deduced amino acid sequence shows 56.7% and 55.9% amino acid identity, respectively, with Cal1 ofSaccharomyces cerevisiae and Chs3 ofCandida albicans. Disruption ofchsD caused no defect in cell growth or morphology during the asexual cycle and caused no decrease in chitin content in hyphae. However, double disruption ofchsA andchsD caused a remarkable decrease in the efficiency of conidia formation, while double disruption ofchsC andchsD caused no defect. Thus it appears thatchsA andchsD serve redundant functions in conidia formation.

Glutamyl-tRNA mediates a switch in RNA polymerase use during chloroplast biogenesis.

Chloroplast genes of higher plants are transcribed by two types of RNA polymerase that are encoded by nuclear (NEP (nuclear‐encoded plastid RNA polymerase)) or plastid (PEP (plastid‐encoded plastid RNA polymerase)) genomes. NEP is largely responsible for the transcription of housekeeping genes during early chloroplast development. Subsequent light‐dependent chloroplast maturation is accompanied by repression of NEP activity and activation of PEP. Here, we show that the plastid‐encoded transfer RNA for glutamate, the expression of which is dependent on PEP, directly binds to and inhibits the transcriptional activity of NEP in vitro. The plastid tRNAGlu thus seems to mediate the switch in RNA polymerase usage from NEP to PEP during chloroplast development.

Positron plasma diagnostics and temperature control for antihydrogen production

Production of antihydrogen atoms by mixing antiprotons with a cold, confined, positron plasma depends critically on parameters such as the plasma density and temperature. We discuss nondestructive measurements, based on a novel, real-time analysis of excited, low-order plasma modes, that provide comprehensive characterization of the positron plasma in the ATHENA antihydrogen apparatus. The plasma length, radius, density, and total particle number are obtained. Measurement and control of plasma temperature variations, and the application to antihydrogen production experiments are discussed.

Chloroplast development in Arabidopsis thaliana requires the nuclear-encoded transcription factor Sigma B

Development of plastids into chloroplasts, the organelles of photosynthesis, is triggered by light. However, little is known of the factors involved in the complex coordination of light‐induced plastid gene expression, which must be directed by both nuclear and plastid genomes. We have isolated an Arabidopsis mutant, abc1, with impaired chloroplast development, which results in a pale green leaf phenotype. The mutated nuclear gene encodes a sigma factor, SigB, presumably for the eubacterial‐like plastid RNA polymerase. Our results provide direct evidence that a nuclear‐derived prokaryotic‐like SigB protein, plays a critical role in the coordination of the two genomes for chloroplast development.

Observation of the 1S–2S transition in trapped antihydrogen

The spectrum of the hydrogen atom has played a central part in fundamental physics over the past 200 years. Historical examples of its importance include the wavelength measurements of absorption lines in the solar spectrum by Fraunhofer, the identification of transition lines by Balmer, Lyman and others, the empirical description of allowed wavelengths by Rydberg, the quantum model of Bohr, the capability of quantum electrodynamics to precisely predict transition frequencies, and modern measurements of the 1S–2S transition by Hänsch to a precision of a few parts in 1015. Recent technological advances have allowed us to focus on antihydrogen—the antimatter equivalent of hydrogen. The Standard Model predicts that there should have been equal amounts of matter and antimatter in the primordial Universe after the Big Bang, but today’s Universe is observed to consist almost entirely of ordinary matter. This motivates the study of antimatter, to see if there is a small asymmetry in the laws of physics that govern the two types of matter. In particular, the CPT (charge conjugation, parity reversal and time reversal) theorem, a cornerstone of the Standard Model, requires that hydrogen and antihydrogen have the same spectrum. Here we report the observation of the 1S–2S transition in magnetically trapped atoms of antihydrogen. We determine that the frequency of the transition, which is driven by two photons from a laser at 243 nanometres, is consistent with that expected for hydrogen in the same environment. This laser excitation of a quantum state of an atom of antimatter represents the most precise measurement performed on an anti-atom. Our result is consistent with CPT invariance at a relative precision of about 2 × 10−10.

DNA-binding and partial nucleoid localization of the chloroplast stromal enzyme ferredoxin : sulfite reductase

Sulfite reductase (SiR) is an important enzyme catalyzing the reduction of sulfite to sulfide during sulfur assimilation in plants. This enzyme is localized in plastids, including chloroplasts, and uses ferredoxin as an electron donor. Ferredoxin‐dependent SiR has been found in isolated chloroplast nucleoids, but its localization in vivo or in intact plastids has not been examined. Here, we report the DNA‐binding properties of SiRs from pea (PsSiR) and maize (ZmSiR) using an enzymatically active holoenzyme with prosthetic groups. PsSiR binds to both double‐stranded and single‐stranded DNA without significant sequence specificity. DNA binding did not affect the enzymatic activity of PsSiR, suggesting that ferredoxin and sulfite are accessible to SiR molecules within the nucleoids. Comparison of PsSiR and ZmSiR suggests that ZmSiR does indeed have DNA‐binding activity, as was reported previously, but the DNA affinity and DNA‐compacting ability are higher in PsSiR than in ZmSiR. The tight compaction of nucleoids by PsSiR led to severe repression of transcription activity in pea nucleoids. Indirect immunofluorescence microscopy showed that the majority of SiR molecules colocalized with nucleoids in pea chloroplasts, whereas no particular localization to nucleoids was detected in maize chloroplasts. These results suggest that SiR plays an essential role in compacting nucleoids in plastids, but that the extent of association of SiR with nucleoids varies among plant species.