Towards robust regional estimates of CO2 sources and sinks using atmospheric transport models

Information about regional carbon sources and sinks can be derived from variations in observed atmospheric CO2 concentrations via inverse modelling with atmospheric tracer transport models. A consensus has not yet been reached regarding the size and distribution of regional carbon fluxes obtained using this approach, partly owing to the use of several different atmospheric transport models. Here we report estimates of surface-atmosphere CO2 fluxes from an intercomparison of atmospheric CO2 inversion models (the TransCom 3 project), which includes 16 transport models and model variants. We find an uptake of CO2 in the southern extratropical ocean less than that estimated from ocean measurements, a result that is not sensitive to transport models or methodological approaches. We also find a northern land carbon sink that is distributed relatively evenly among the continents of the Northern Hemisphere, but these results show some sensitivity to transport differences among models, especially in how they respond to seasonal terrestrial exchange of CO2. Overall, carbon fluxes integrated over latitudinal zones are strongly constrained by observations in the middle to high latitudes. Further significant constraints to our understanding of regional carbon fluxes will therefore require improvements in transport models and expansion of the CO2 observation network within the tropics.     

A silicon transporter in rice

Silicon is beneficial to plant growth and helps plants to overcome abiotic and biotic stresses by preventing lodging (falling over) and increasing resistance to pests and diseases, as well as other stresses. Silicon is essential for high and sustainable production of rice, but the molecular mechanism responsible for the uptake of silicon is unknown. Here we describe the Low silicon rice 1 (Lsi1) gene, which controls silicon accumulation in rice, a typical silicon-accumulating plant. This gene belongs to the aquaporin family and is constitutively expressed in the roots. Lsi1 is localized on the plasma membrane of the distal side of both exodermis and endodermis cells, where casparian strips are located. Suppression of Lsi1 expression resulted in reduced silicon uptake. Furthermore, expression of Lsi1 in Xenopus oocytes showed transport activity for silicon only. The identification of a silicon transporter provides both an insight into the silicon uptake system in plants, and a new strategy for producing crops with high resistance to multiple stresses by genetic modification of the root's silicon uptake capacity.     

Self-formation of functional adenohypophysis in three-dimensional culture

The adenohypophysis (anterior pituitary) is a major centre for systemic hormones. At present, no efficient stem-cell culture for its generation is available, partly because of insufficient knowledge about how the pituitary primordium (Rathke's pouch) is induced in the embryonic head ectoderm. Here we report efficient self-formation of three-dimensional adenohypophysis tissues in an aggregate culture of mouse embryonic stem (ES) cells. ES cells were stimulated to differentiate into non-neural head ectoderm and hypothalamic neuroectoderm in adjacent layers within the aggregate, and treated with hedgehog signalling. Self-organization of Rathke's-pouch-like three-dimensional structures occurred at the interface of these two epithelia, as seen in vivo, and various endocrine cells including corticotrophs and somatotrophs were subsequently produced. The corticotrophs efficiently secreted adrenocorticotropic hormone in response to corticotrophin releasing hormone and, when grafted in vivo, these cells rescued the systemic glucocorticoid level in hypopituitary mice. Thus, functional anterior pituitary tissue self-forms in ES cell culture, recapitulating local tissue interactions.     

Fe-1.5C-1.5Cr-2.0Al超高碳钢的等温组织及力学性能

利用XRD、SEM、TEM、维氏硬度计和拉伸试验机对Fe-1．5C-1．5Cr-2．0Al超高碳钢经300℃等温淬火后的组织及力学性能进行了研究．组织观察与分析表明，等温淬火组织为超细下贝氏体铁素体、残余奥氏体和未溶渗碳体，并随等温时间延长，残余奥氏体体积分数减少，组织细化程度增加．研究发现：等温淬火2—10h，屈服强度为1411—1568MPa，抗拉强度为1632—1744MPa，总延伸率为6．9％～8．5％，硬度为515—532HV。随等温时间的延长，强度和硬度升高，塑性下降．     

CO2 regulator SLAC1 and its homologues are essential for anion homeostasis in plant cells

The continuing rise in atmospheric [CO2] is predicted to have diverse and dramatic effects on the productivity of agriculture, plant ecosystems and gas exchange. Stomatal pores in the epidermis provide gates for the exchange of CO2 and water between plants and the atmosphere, processes vital to plant life. Increased [CO2] has been shown to enhance anion channel activity proposed to mediate efflux of osmoregulatory anions (Cl- and malate(2-)) from guard cells during stomatal closure. However, the genes encoding anion efflux channels in plant plasma membranes remain unknown. Here we report the isolation of an Arabidopsis gene, SLAC1 (SLOW ANION CHANNEL-ASSOCIATED 1, At1g12480), which mediates CO2 sensitivity in regulation of plant gas exchange. The SLAC1 protein is a distant homologue of bacterial and fungal C4-dicarboxylate transporters, and is localized specifically to the plasma membrane of guard cells. It belongs to a protein family that in Arabidopsis consists of four structurally related members that are common in their plasma membrane localization, but show distinct tissue-specific expression patterns. The loss-of-function mutation in SLAC1 was accompanied by an over-accumulation of the osmoregulatory anions in guard cell protoplasts. Guard-cell-specific expression of SLAC1 or its family members resulted in restoration of the wild-type stomatal responses, including CO2 sensitivity, and also in the dissipation of the over-accumulated anions. These results suggest that SLAC1-family proteins have an evolutionarily conserved function that is required for the maintenance of organic/inorganic anion homeostasis on the cellular level.     

Sequence of a novel simian immunodeficiency virus from a wild-caught African mandrill

Since the isolation of an HIV-2-related virus from captive macaques (SIVMAC), the origin of human immunodeficiency viruses, a much debated subject, has been attributed to monkeys. The sequence of SIVAGM, which is derived from a naturally infected African green monkey, shows equal relatedness to HIV-1 and HIV-2, suggesting that the derivation of these viruses from SIVAGM is unlikely. Recent sequence analysis of SIV from a captive sooty mangabey (SIVMAC), however, shows its close relatedness to HIV-2 and SIVMAC, indicating a possible origin of HIV-2 and SIVMAC from SIVSM (refs 4, 7, 9). We report here the sequence of a novel simian lentivirus, SIVMND, isolated from a wild-caught mandrill in Africa. It is distinct from the three other main groups, HIV-1, HIV-2/SIVMAC/SIVSM and SIVAGM, and therefore represents a fourth main group of primate lentiviruses. Phylogenetic analysis indicates that these four main virus groups might have diverged from a common ancestor at about the same time, long before the spread of AIDS in humans.     

Peptide antigens for gamma/delta T cells

γδ T cells express adaptive antigen receptors encoded by rearranging genes. Their diversity is highest in the small region of TCR V–J junctions, especially in the δ chain, which should enable the γδ TCRs to distinguish differences in small epitopes. Indeed, recognition of small molecules, and of an epitope on a larger protein has been reported. Responses to small non-peptides known as phospho-antigens are multi-clonal yet limited to a single γδ T cell subset in humans and non-human primates. Responses to small peptides are multi-clonal or oligo-clonal, include more than one subset of γδ T cells, and occur in rodents and primates. However, less effort has been devoted to investigate the peptide responses. To settle the questions of whether peptides can be ligands for the γδ TCRs, and whether responses to small peptides might occur normally, peptide binding will have to be demonstrated, and natural peptide ligands identified.     

Avian flu: isolation of drug-resistant H5N1 virus

The persistence of H5N1 avian influenza viruses in many Asian countries and their ability to cause fatal infections in humans have raised serious concerns about a global flu pandemic. Here we report the isolation of an H5N1 virus from a Vietnamese girl that is resistant to the drug oseltamivir, which is an inhibitor of the viral enzyme neuraminidase and is currently used for protection against and treatment of influenza. Further investigation is necessary to determine the prevalence of oseltamivir-resistant H5N1 viruses among patients treated with this drug.