Implications of symbiotic nitrogen fixation by desert plants

There is little information available regarding symbiotic nitrogen fixation by desert plants, particularly with respect to the group of nodulated non-legumes. Early investigations of nodules on non-legumes were contemporary with early studies of the Leguminoseae; however, comparatively little is known even now regarding the extent to which non-legumes fix nitrogen. A review of literature regarding changes in concepts of nitrogen fixation by legumes and nodulated non-legumes is presented. Evidence from recent studies on nodulated non-legumes, including those in desert areas, indicates some 31 species of 21 genera in 12 new or previously unrecognized plant families show nodulation with implications of nitrogen fixation. Some biological aspects of symbiotic nitrogen fixation are discussed, and reports in the literature of nitrogen fixation in natural plant populations are reviewed. Nitrogen fixation reactions in the desert environment are considered in terms of the areas of investigation needed to help define (1) the magnitude of nitrogen fixation, (2) the extent of nodulation in non-legume plants, and (3) factors affecting this nodulation in the desert ecosystem.     

The raccoon, Procyon Iotor, in Wyoming

Recent distribution maps show raccoon as occupying only the extreme eastern - northeastern portion of Wyoming. However, there is substantial evidence that raccoon are common throughout Wyoming and currently inhabit all the major and many of the minor drainages throughout Wyoming.     

Ocean-like water in the Jupiter-family comet 103P/Hartley 2

For decades, the source of Earth's volatiles, especially water with a deuterium-to-hydrogen ratio (D/H) of (1.558?±?0.001)?×?10(-4), has been a subject of debate. The similarity of Earth's bulk composition to that of meteorites known as enstatite chondrites suggests a dry proto-Earth with subsequent delivery of volatiles by local accretion or impacts of asteroids or comets. Previous measurements in six comets from the Oort cloud yielded a mean D/H ratio of (2.96?±?0.25)?×?10(-4). The D/H value in carbonaceous chondrites, (1.4?±?0.1)?×?10(-4), together with dynamical simulations, led to models in which asteroids were the main source of Earth's water, with ≤10 per cent being delivered by comets. Here we report that the D/H ratio in the Jupiter-family comet 103P/Hartley 2, which originated in the Kuiper belt, is (1.61?±?0.24)?×?10(-4). This result substantially expands the reservoir of Earth ocean-like water to include some comets, and is consistent with the emerging picture of a complex dynamical evolution of the early Solar System.     

Does the brain know the physics of specular reflection?

Images of artificial and natural scenes typically contain many highlights generated by mirror-like reflection from glossy surfaces. Until recently, computational models of visual processes have tended to regard highlights as obscuring the structure of the underlying scene. The truth is that, on the contrary, highlights are rich in local geometric information. Here we report that the three-dimensional appearance of a highlight on a computer-simulated stereoscopic curved surface affects observers' judgment of surface gloss. We also show that the 3-D appearance of a highlight affects the perception of surface curvature--that is, it can force an ambiguous convex-concave figure to change state. We thus conclude that human visual analysis seems to employ a physical model of the interaction of light with curved surfaces, a model firmly based on ray optics and differential geometry.     

Sequence, structure and activity of phosphoglycerate kinase: a possible hinge-bending enzyme.

The fitting of sequenced peptides to a high-resolution X-ray map of phosphoglycerate kinase has yielded the complete sequence and structure of the horse muscle enzyme. Metal ADP and ATP substrates are bound to one of the two widely separated domains in an environment that seems unsuitable for phosphoglycerate binding. The most plausible binding site for the phosphoglycerate substrate is on the other domain about 10 A from the ATP, which implies the possibility of a large scale hinge-bending of the domains to bring the two substrates together in a water-free environment for catalysis.     

Forced synthesis of trace amounts of juvenile hormone II from propionate by corpora allata of a juvenile hormone III-producing insect

Corpora allata of the cockroach Diploptera punctata normally synthesize only the isoprenoid juvenile hormone III (JH III). Only under extreme in vitro conditions (absence of carbon sources other than propionate) do they produce trace amounts of the homoisoprenoid JH II in addition to JH III. The specificity of the in vitro synthesis of JH III by D. punctata is thus consistent with the observed lack of homoisoprenoid JHs in this insect.     

通过镍(II)-硫键和碘离子基元反应有理合成碘-二硫醇盐桥联的双核镍-镍配合物

本文报道由于碘离子对不稳定的Ni(II)-S(芳基硫醇盐)键的亲核作用,使得Fe(CO)412和Ni(SR)2(dppe(SR=芳基硫醇盐)之间的反应生成NiI2(dppe).含碘和二芳基硫醇盐离子桥联的Ni-Ni双核配合物[(dppe)Ni(μ-I)(μ-pdt)Ni(dppe)]I和[(dppe)Ni(μ-I)(μ-edt)Ni(dppe)]I可方便地由[NiI2(dppe)]和[Ni(pdt)(dppe)]或[Ni(edt)(dppe)]在二氯甲烷的溶液中的反应制得;该类反应可认为是由于硫醇盐离子基团中S-供体上的孤对电子对Ni-I键的进攻所致.另一方面,我们观察到[FeCp(CO)2I]和[Ni(pdt)(dppe)]或[Ni(edt)(dppe)]在二氯甲烷中的反应极其缓慢;但当向上述反应体系中加入NH4PF6进行复分解置换后,源于碘离子和Ni(II)-S键的作用同样可得到含碘与二芳基硫醇盐离子桥联的Ni-Ni双核配合物[(dppe)Ni(μ-I)(μ-pdt)Ni(dppe)]PF6和 [(dppe)Ni(μ-I)(μ-edt)Ni(dppe)]PF6.实验结果说明在本文所讨认的镍(II)-硫醇盐离子-膦配合物中,Ni(II)-S键的反应活性随桥联的第二金属离子和不同的碘离子基元而改变.     

An infrared flash contemporaneous with the gamma-rays of GRB 041219a

The explosion that results in a cosmic gamma-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks, gamma-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks.