This Week in Science

Science  19 May 2006:
Vol. 312, Issue 5776, pp. 969
  1. Controlling the Coming of Catkins

    CREDIT: BÖHLENIUS ET AL.

    The regulation of flowering in annual plants is controlled by a pair of genes, FT and CO. Are similar genes also involved in regulating flowering time in trees? The juvenile phase in trees can last for decades before the first flower is formed. During this time, the tree is nonresponsive to environmental factors that potentially influence flowering time. Böhlenius et al. (p. 1040, published online 4 May) show that the FT ortholog from Populus trees (poplars, aspen, and cottonwoods) is a critical determinant of flowering time in trees. The poplar FT is also responsible for a completely different developmental process in trees, the timing of the short-day induced growth cessation and bud set that occurs in the fall.

  2. Heavy Metal and Hard Rock

    Drilling through a complete sequence of layers of the Earth's crust into the underlying pristine igneous rocks is a major goal of earth science. The thinnest crust occurs near fast-spreading mid-ocean ridges, so bore holes have targeted these regions. Wilson et al. (p. 1016, published online 20 April) drilled a 1.6-kilometer-deep bore hole through intact crust near the East Pacific Rise to reach gabbro, a layer of dark crystalline igneous rock formed from solidified magma that underlies much of the Earth's ocean floor. Determining the depth to gabbro layers confirms that magma chambers form at shallow levels in the crust at very high spreading rates; gabbros are brought up into these chambers from depth. Also, seismic bands do not correspond to compositional rock layers, implying that seismic velocities are controlled more by porosity than rock type.

  3. Poised for Polymerization

    CREDIT: SUN ET AL.

    The networks of conjugated π-orbitals in conducting polymers are stabilized either by bulky polyatomic side groups or phenyl groups incorporated within the backbone chains. Sun et al. (p. 1030; see the Perspective by Baughman) have prepared a polymer composed of strictly alternating C=C double and C≡C triple bonds, with only iodine atoms as side groups. The synthesis relied on prior templating of the diiododiacetylene monomer in a cocrystal with a dinitrile oxalamide host. Packing contacts between the nitriles and iodines allow the host structure to align the monomers in a column with relative spacings that changed little after polymerization. The product is a potential precursor to carbyne, a hypothesized but elusive linear allotrope of carbon.

  4. Spin Sequences

    The control of coupling between spins in small structures could find use in spintronics and quantum computing. Hirjibehedin et al. (p. 1021, published online 30 March; see the Perspective by Brune) assembled chains of Mn atoms with a scanning tunneling microscope on a thin insulating surface (a monolayer of CuN grown on a Cu surface). They then used inelastic tunneling spectroscopy to measure spin excitation spectra as a function of chain length (up to 10 atoms) under cryogenic conditions. Comparison of the spectra with a Heisenberg model of an open spin chain with antiferromagnetic exchange coupling revealed the collective spin configurations as well as the strength of the coupling.

  5. Selective Si-H Scission

    Breaking a chemical bond by exciting its stretching vibration is an appealing idea that rarely works because the energy redistributes rapidly into other vibrational or rotational motions. Liu et al. (p. 1024; see the Perspective by Tully) found that H atoms adsorbed on a silicon (111) surface can be expelled as H2 by irradiation with intense pulses of infrared light tuned to the Si-H stretching frequency. Although local heating of the surface could also cleave the Si-H bonds, the authors rule out this thermal mechanism by irradiating a mixture of adsorbed H and D atoms under the same conditions. Whereas simple heating of the surface favors D2 over H2 production by ∼17:1, resonant excitation of the Si-H stretch reverses the selectivity to favor H2 by a factor of 200.

  6. Beating a Bottleneck

    Knudsen diffusion occurs when the mean free path of atoms or molecules is relatively long compared to the pore or channel through which they move, so that wall collisions become more frequent than those between particles. This model holds for pores between 2 and 50 nanometers, but what happens during flow in smaller channels? Holt et al. (p. 1034, see the cover and the Perspective by Sholl and Johnson) fabricated membranes using double- and multiwalled carbon nanotubes to form the pores. For gases, flow rates were an order of magnitude greater than those predicted by Knudsen diffusion, and water flow rates greatly exceeded values calculated from hydrodynamics. The authors argue that the enhanced transport is caused by the smoothness of the inner nanotube surfaces, in agreement with results from computer simulations.

  7. Evolution by Reduction?

    The origins of eukaryotes remain controversial and somewhat enigmatic. Kurland et al. (p. 1011) provide a counterpoint to current models in which the eukaryotic cell is derived from structurally and genetically less complex prokaryotic cells. On the basis of genomic and proteomic evidence, they suggest that the essence of eukaryotic cellular complexity existed in the common ancestor of eucarya, bacteria, and archaea, and that the bacteria and archaea have evolved by genome reduction driven by specialization for fast growth and cell division and/or adaptation to extreme environments.

  8. Being Prepared

    Planning ahead requires a host of cognitive skills, not the least of which is the capacity to foresee a future state of need, provocatively termed mental time travel. There is persuasive evidence that scrub jays can relocate their food caches to avoid losing them to their observant neighbors, thus preserving them for future consumption (see Dally et al., published online May 18). Mulcahy and Call (p. 1038; see the Perspective by Suddendorf) present a series of experiments that assess whether bonobos and orangutans can be coaxed to display these skills. Both species of great apes can select a suitably useful object, keep it with them overnight, and bring it back for use the next day as a tool for retrieving a food reward.

  9. Special Speciation in Madagascar

    CREDIT: WILMÉ ET AL.

    A high percentage of the fauna and flora of Madagascar is endemic to the island, a consequence of its isolation from the African mainland since the Jurassic. Madagascar is also noted for a high degree of local endemism within the island, often to particular watersheds, a pattern that has long puzzled biogeographers. On the basis of a database of species distributions in relation to rivers and watersheds, Wilmé et al. (p. 1063) show how patterns of climate fluctuation have reinforced local isolation of populations, particularly of forest-dwelling species, to give rise to conditions suitable for speciation on a local scale.

  10. Marshalling DNA Defenses

    Cells recognize damaged DNA and initiate a complex signaling mechanism that help cells cope with the damage and initiate repair. But it is not just the enzymes required for DNA repair that undergo increased expression in response to DNA damage—other events such as progression through the cell cycle, stress responses, and metabolic pathways are also regulated. Workman et al. (p. 1054) used a systems-level approach to map such signaling pathways that respond to DNA damage. The results revealed unanticipated regulatory interactions and pave the way to when such maps may be used to predict the patient-specific effects of particular drugs.

  11. Who Gets the Credit?

    In working backward from outcomes to behavior or in strategic planning for future scenarios, one important issue is who gets the credit (and how much) for the eventual result. In the trust game, the first player has to decide how much money to invest, and the second player has to decide how much of the multiplied investment to give back. Tomlin et al. (p. 1047) have carried out a large-scale simultaneous brain imaging study and suggest that different regions of the cingulate cortex become active when what the “other” player has chosen to do is revealed, compared with situations when “I” have done the choosing.

  12. Controlling the Synapse

    Synapses in the neuromuscular junction are key components involved in control of muscle movement. Kittel et al. (p. 1051, published online 13 April; see the Perspective by Atwood) describe the role of Drosophila Bruchpilot (BRP), a coiled-coil domain protein, in the establishment and maintenance of synapses. BRP was localized to donut-shaped structures centered at the transmitter release sites (active zones) of Drosophila neuromuscular synapses. In mutants lacking BRP, presynaptic membranes were defective. The authors suggest that BRP is needed to form a fully functional synapse and might mediate presynaptic changes in vivo by establishing a close proximity between Ca2+ channels and vesicles at release sites.

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