Guard cell abscisic acid signalling and engineering drought hardiness in plants

Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.     

Interhemispheric climate links revealed by late-glacial cooling episode in southern Chile

Understanding the relative timings of climate events in the Northern and Southern hemispheres is a prerequisite for determining the causes of abrupt climate changes. But climate records from the Patagonian Andes and New Zealand for the period of transition from glacial to interglacial conditions--about 14.6-10 kyr before present, as determined by radiocarbon dating--show varying degrees of correlation with similar records from the Northern Hemisphere. It is necessary to resolve these apparent discrepancies in order to be able to assess the relative roles of Northern Hemisphere ice sheets and oceanic, atmospheric and astronomical influences in initiating climate change in the late-glacial period. Here we report pollen records from three sites in the Lake District of southern Chile (41 degrees S) from which we infer conditions similar to modern climate between about 13 and 12.2 14C kyr before present (BP), followed by cooling events at about 12.2 and 11.4 14C kyr BP, and then by a warming at about 9.8 14C kyr BP. These events were nearly synchronous with important palaeoclimate changes recorded in the North Atlantic region, supporting the idea that interhemispheric linkage through the atmosphere was the primary control on climate during the last deglaciation. In other regions of the Southern Hemisphere, where climate events are not in phase with those in the Northern Hemisphere, local oceanic influences may have counteracted the effects that propagated through the atmosphere.     

Guide to the draft human genome

There are a number of ways to investigate the structure, function and evolution of the human genome. These include examining the morphology of normal and abnormal chromosomes, constructing maps of genomic landmarks, following the genetic transmission of phenotypes and DNA sequence variations, and characterizing thousands of individual genes. To this list we can now add the elucidation of the genomic DNA sequence, albeit at 'working draft' accuracy. The current challenge is to weave together these disparate types of data to produce the information infrastructure needed to support the next generation of biomedical research. Here we provide an overview of the different sources of information about the human genome and how modern information technology, in particular the internet, allows us to link them together.     

Involvement of chemokine receptors in breast cancer metastasis

Breast cancer is characterized by a distinct metastatic pattern involving the regional lymph nodes, bone marrow, lung and liver. Tumour cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokines and their receptors. Here we report that the chemokine receptors CXCR4 and CCR7 are highly expressed in human breast cancer cells, malignant breast tumours and metastases. Their respective ligands CXCL12/SDF-1alpha and CCL21/6Ckine exhibit peak levels of expression in organs representing the first destinations of breast cancer metastasis. In breast cancer cells, signalling through CXCR4 or CCR7 mediates actin polymerization and pseudopodia formation, and subsequently induces chemotactic and invasive responses. In vivo, neutralizing the interactions of CXCL12/CXCR4 significantly impairs metastasis of breast cancer cells to regional lymph nodes and lung. Malignant melanoma, which has a similar metastatic pattern as breast cancer but also a high incidence of skin metastases, shows high expression levels of CCR10 in addition to CXCR4 and CCR7. Our findings indicate that chemokines and their receptors have a critical role in determining the metastatic destination of tumour cells.     

New hominin genus from eastern Africa shows diverse middle Pliocene lineages

Most interpretations of early hominin phylogeny recognize a single early to middle Pliocene ancestral lineage, best represented by Australopithecus afarensis, which gave rise to a radiation of taxa in the late Pliocene. Here we report on new fossils discovered west of Lake Turkana, Kenya, which differ markedly from those of contemporary A. afarensis, indicating that hominin taxonomic diversity extended back, well into the middle Pliocene. A 3.5 Myr-old cranium, showing a unique combination of derived facial and primitive neurocranial features, is assigned to a new genus of hominin. These findings point to an early diet-driven adaptive radiation, provide new insight on the association of hominin craniodental features, and have implications for our understanding of Plio-Pleistocene hominin phylogeny.     

Nuclear fission modes and fragment mass asymmetries in a five-dimensional deformation space

Nuclei undergoing fission can be described by a multi-dimensional potential-energy surface that guides the nuclear shape evolution--from the ground state, through intermediate saddle points and finally to the configurations of separated fission fragments. Until now, calculations have lacked adequate exploration of the shape parameterization of sufficient dimensionality to yield features in the potential-energy surface (such as multiple minima, valleys, saddle points and ridges) that correspond to characteristic observables of the fission process. Here we calculate and analyse five-dimensional potential-energy landscapes based on a grid of 2,610,885 deformation points. We find that observed fission features--such as the distributions of fission fragment mass and kinetic energy, and the different energy thresholds for symmetric and asymmetric fission--are very closely related to topological features in the calculated five-dimensional energy landscapes.     

Enhancement of the high-magnetic-field critical current density of superconducting MgB2 by proton irradiation

Magnesium diboride, MgB2, has a relatively high superconducting transition temperature, placing it between the families of low- and high-temperature (copper oxide based) superconductors. Supercurrent flow in MgB2 is unhindered by grain boundaries, making it potentially attractive for technological applications in the temperature range 20-30 K. But in the bulk material, the critical current density (Jc) drops rapidly with increasing magnetic field strength. The magnitude and field dependence of the critical current are related to the presence of structural defects that can 'pin' the quantized magnetic vortices that permeate the material, and a lack of natural defects in MgB2 may be responsible for the rapid decline of Jc with increasing field strength. Here we show that modest levels of atomic disorder induced by proton irradiation enhance the pinning of vortices, thereby significantly increasing Jc at high field strengths. We anticipate that either chemical doping or mechanical processing should generate similar levels of disorder, and so achieve performance that is technologically attractive in an economically viable way.     

The Earth's mantle

Seismological images of the Earth's mantle reveal three distinct changes in velocity structure, at depths of 410, 660 and 2,700 km. The first two are best explained by mineral phase transformations, whereas the third-the D" layer-probably reflects a change in chemical composition and thermal structure. Tomographic images of cold slabs in the lower mantle, the displacements of the 410-km and 660-km discontinuities around subduction zones, and the occurrence of small-scale heterogeneities in the lower mantle all indicate that subducted material penetrates the deep mantle, implying whole-mantle convection. In contrast, geochemical analyses of the basaltic products of mantle melting are frequently used to infer that mantle convection is layered, with the deeper mantle largely isolated from the upper mantle. We show that geochemical, seismological and heat-flow data are all consistent with whole-mantle convection provided that the observed heterogeneities are remnants of recycled oceanic and continental crust that make up about 16 and 0.3 per cent, respectively, of mantle volume.