This Week in Science

Science  30 Jul 2004:
Vol. 305, Issue 5684, pp. 569
  1. Controlling Interface Spin

    CREDIT: YAMADA ET AL.

    The magneto-electronic properties of heterojunction structures formed between magnetic thin films and insulating layers are attractive for potential device applications. However, the behavior of such structures has been unpredictable, and techniques are needed that can investigate the influence of interface region. Using magnetization-induced second-harmonic generation, Yamada et al. (p. 646) show that they can probe and characterize the magnetization of buried interfaces formed between manganite and insulating thin films. Moreover, by grading the doping level of the interface region, they show how the properties can be altered in a controlled manner.

  2. Strained and Stretched Nanoparticles

    The electronic and optical properties of a material can change on going from bulk materials to the nanoscale. Gilbert et al. (p. 651, published online 1 July 2004) show how confinement effects can affect the bonding and packing of atoms. They use a number of techniques to measure the lattice structure and internal strains in 3-nanometer particles of zinc sulfide. A complex pattern of internal strains results as the particles attempt to lower the surface energy. These strains cause a reduction in the overall ordering and a stiffening of the lattice. When metals are deformed, the crystalline grains can rotate and realign, much in the way that painted shapes will stretch and warp when a canvas is pulled in a specific direction. Shan et al. (p. 654; see the Perspective by Ma) find that in nanocrystalline nickel, this type of deformation dominates, unlike the situation with coarser grained metals, where the production of grain boundary defects and dislocations accommodates most of the deformation energy. These results confirm many observations obtained from computer simulations and should help guide the design of optimum metals and alloys.

  3. Lunar Meteorite Phones Home

    A lunar meteorite found in the Sultanate of Oman (Sayh al Uhaymir 169) consists of four different impact breccias and is enriched in potassium, rare earth elements, and phosphorus. Gnos et al. (p. 657; see the Perspective by Korotev) used isotopic systematics to date the four impact events that occurred while the rock was at or near the surface of the Moon. The impact event dates of 3900 million years ago (Ma), 2800 Ma, 200 Ma, and <0.34 Ma, along with the chemical enrichments, help to pinpoint the source of the meteorite in the Lalande impact crater on the Moon. The dated impact events will allow lunar geologists to refine the ages of the different stratigraphic units associated with this meteorite into a more global model of the evolution of the Moon.

  4. Removing Plant Defenses

    In order to resist herbivore attack, plants use direct defenses, such as toxins and digestibility reducers, as well as indirect defenses that affect components of the plants' community (such as natural enemies and diseases). Plant defenses can be expressed constitutively or produced in response to an attacking pathogen or herbivore. Kessler et al. (p. 665, published online 1 July 2004; see the Perspective by Dicke et al.) transformed the wild tobacco species Nicotiana attenuata, to silence three genes coding for enzymes in the jasmonate signaling pathway, which is known to be involved in induced plant defense. When planted into native habitats, the transformed plants were more vulnerable not only to their specialist herbivores but also to other herbivore species.

  5. Pop Goes the Mitochondrion

    In cells undergoing apoptosis or cell death, mitochondria, the powerhouses of the cell, often have a key role. Not only is cellular metabolism shut down, but mitochondria release molecules into the cytoplasm that further promote cell death. Substantial controversy has surrounded the mechanisms by which these processes occur. Green and Kroemer (p. 626) review the role of mitochondria in cell death. Permeabilization of the mitochondria can be the point-of-no-return that seals the fate of a cell, and numerous strategies are envisioned to alter these processes therapeutically to benefit patients suffering from a range of illnesses from cancer and heart failure to neurodegeneration.

  6. Herbivores Drive Diversity

    Habitat specialization and beta-diversity—the change in species composition between sites—may explain a large part of the overall diversity within tropical forests. However, why beta-diversity should be higher in the tropics remains unclear. To test the hypothesis that herbivores promote habitat specialization, Fine et al. (p. 663; see the Perspective by Marquis) performed reciprocal transplant experiments of specialist tree seedlings between soil types in the Peruvian Amazon, and also manipulated their herbivores. Habitat specialization of plants resulted from an interaction of herbivore pressure with soil type, which suggests that herbivores drive beta-diversity patterns by maintaining habitat specialization.

  7. Diffusion Goes Electronic

    CREDIT: BARTELS ET AL.

    The atomic-scale resolution of the scanning tunneling microscope has been paired with the temporal resolution afforded by femtosecond laser pulses to differentiate electronically excited molecular diffusion from thermally induced diffusion. Bartels et al. (p. 648, published online 24 June 2004) excited CO molecules on the anisotropic Cu(110) surface with 200-femtosecond laser pulses at a wavelength of 405 nanometers. Unlike diffusion at thermal or equilibrium conditions, which occurs along the rows of atoms formed by Cu atoms on this surface, the nonequilibrated electronically excited CO molecules diffused over the rows as well. A phenomenological model can account for these results in terms of electronic excitation of the CO-substrate vibrations.

  8. Worming into Whale Bones

    A new genus of annelid worm that is related to hydrothermal vent worms has been discovered on the corpse of a gray whale found several thousands meters deep off the coast of California. Rouse et al. (p. 668) have named the genus Osedax. The female worms possess tubes from which red plumes emerge and which harbor numerous, nonfeeding, dwarf male worms. Like vent worms, Osedax worms are gutless and contain bacterial symbionts. The worms burrow into the whale bones and form rootlike structures which contain the symbiotic organotrophic bacteria that mobilize nutrients from the whale skeleton.

  9. The Genomics Underlying Acne

    Propionibacterium acnes is a ubiquitous, human skin-dwelling organism involved in the etiology of acne. Brüggemann et al. (p. 671) have sequenced and analyzed the complete genome of P. acnes. The genome data offer information on the bacterial antigens and tissue-damaging enzymes that may cause the inflammatory reactions underlying the disease process.

  10. Freeze-Frames of Motor Movement

    CREDIT: NITTA ET AL.

    Kinesin motor proteins move along microtubules by rapidly alternating between tightly bound and detached states. Movement is adenosine triphosphate (ATP)-dependent and changes in binding affinity are associated with the ATPase cycle. Nitta et al. (p. 678) report crystal structures of the monomeric kinesin KIF1A with three transition state analogs. Kinesin alternately uses two loops to bind microtubules with an intermediate state in which neither loop binds. When KIF1A is working, it likely alternates between a tight-binding state with the affinity biased toward the forward tubulin subunit, and a weak-binding state that allows one-dimensional diffusion.

  11. Reconstituting Prion Disease in Mice

    The prion hypothesis postulates the existence of infectious proteins capable of propagating disease. Legname et al. (p. 673; see the news story by Couzin) now present evidence that a novel strain of prion disease can be induced in mice injected with recombinant prion proteins. Brain extracts from these mice could then be used to infect other mice to cause a neuropathological disorder distinct from other known strains of prion disease.

  12. Host-Parasite Gene Transfer in Plants

    The parasitic plant family Rafflesiaceae resisted definitive taxonomic placement since its initial description nearly two centuries ago. Recently, a study placed it firmly in the order Malpighiales, based on the mitochondrial gene matR. Davis and Wurdack (p. 676, published online 15 July 2004) have reexamined this question by adding all family representatives of Malpighiales across four genetic loci spanning the nuclear and mitochondrial genomes. The nuclear DNA, and one mitochondrial locus, confirmed the position of Rafflesiaceae within Malpighiales. However, the other mitochondrial locus, nad1B-C, places Rafflesiaceae in the family Vitaceae, which is in a different order. These incompatible phylogenetic results appear to provide a new example of horizontal gene transfer between species—horizontal gene transfer mediated by a plant host-parasite system.

  13. Crustal Detachment

    The Sierra Nevada mountain range in California sits on a relatively thin crust compared to the elevation of the mountains, which has led to the hypothesis that part of the lower crust has been removed. Boyd et al. (p. 660) used seismic imaging to determine the geometry and composition of the crust beneath the mountains. They found evidence for a remnant of older crust that has separated from the upper crust and is being bent downward into the mantle. This delamination of the crust helps to explain the elevation of the mountains and the growth and evolution of continental crust.

  14. Small Change, Big Effect

    Isoforms of cytochrome P450 (CYP) are responsible for the oxidative metabolism of more than 90% of drugs in humans, and one isoform, CYP 3A4, is responsible for over 50% of hepatic drug metabolism. Now Williams et al. (p. 683, published online 15 July 2004) have determined the crystal structures of CYP 3A4, bound to either a substrate, to an inhibitor, or unliganded. The structures show very little change either on substrate or inhibitor binding. The substrate is bound in a peripheral binding site that may be involved in initial substrate binding or in binding to allosteric effectors. Conformational changes may be required for movement of substrate to the active site.

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