Impairment of endothelium-dependent arterial relaxation by lysolecithin in modified low-density lipoproteins

Atherosclerosis in animals and humans is associated with an unresponsiveness of arteries and arterioles to endothelium-dependent vasodilators--agents acting on smooth muscle indirectly by stimulating the release from endothelial cells of a vasodilator principle (endothelium-derived relaxing factor). Altered vasomotor regulation in atherosclerosis could partly reflect an injurious action of abnormal lipoproteins on endothelium. Recently, 'cell-modified' or 'oxidized' low-density lipoprotein (EC-LDL) has received increasing attention because of its potential cytotoxic and atherogenic properties. We report here that arteries exposed to EC-LDL in vitro show an endothelium-dependent vasoregulatory impairment closely resembling that of atherosclerotic arteries. Our results indicate that transfer of lysolecithin from EC-LDL to endothelial membranes produces a selective unresponsiveness to receptor-regulated endothelium-dependent vasodilators.     

A ferric-chelate reductase for iron uptake from soils

Iron deficiency afflicts more than three billion people worldwide, and plants are the principal source of iron in most diets. Low availability of iron often limits plant growth because iron forms insoluble ferric oxides, leaving only a small, organically complexed fraction in soil solutions. The enzyme ferric-chelate reductase is required for most plants to acquire soluble iron. Here we report the isolation of the FRO2 gene, which is expressed in iron-deficient roots of Arabidopsis. FRO2 belongs to a superfamily of flavocytochromes that transport electrons across membranes. It possesses intramembranous binding sites for haem and cytoplasmic binding sites for nucleotide cofactors that donate and transfer electrons. We show that FRO2 is allelic to the frd1 mutations that impair the activity of ferric-chelate reductase. There is a nonsense mutation within the first exon of FRO2 in frd1-1 and a missense mutation within FRO2 in frd1-3. Introduction of functional FRO2 complements the frd1-1 phenotype in transgenic plants. The isolation of FRO2 has implications for the generation of crops with improved nutritional quality and increased growth in iron-deficient soils.     

地理信息系统数据标准研究

地理信息是近年来地学界比较热门的话题,它是信息高速公路建设中全球空间数据基础设施的主要内容。本文地地理信息系统技术和标准的发展问题做了系统的分析,通过地理信息系统标准在政府、国家和国际间的历程,并结合我国的发展状况,展现了地理信息共享的地理信息系统发展趋势。     

Shoemaker crater as the source of most ejecta blocks on the asteroid 433 Eros

The loose material--regolith--on the surfaces of asteroids is thought to represent ballistically emplaced ejecta from impacts but the identification of source craters and the detailed study of the regolith modification have been hampered by the limited spatial resolution and area coverage of the few asteroids imaged by spacecraft. Here we report the results of global mapping of the asteroid 433 Eros from high-resolution images obtained by the NEAR-Shoemaker spacecraft. Based on the images and ejecta-emplacement models, we suggest that most large ejecta blocks on Eros originate from a relatively young 7.6-km-diameter crater. A large fraction of the ejecta from impacts pre-dating that crater has apparently been buried or eroded. The images also show evidence for the action of a variety of sorting environments for regolith particles after they are deposited on the surface.     

Planetary science: constant illumination at the lunar north pole

Images returned by the spacecraft Clementine have been used to produce a quantitative illumination map of the north pole of the Moon, revealing the percentage of time that points on the surface are illuminated during the lunar day. We have used this map to identify areas that are constantly illuminated during a lunar day in summer and which may therefore be in permanent sunlight. All are located on the northern rim of Peary crater, close to the north pole. Permanently sunlit areas represent prime locations for lunar outpost sites as they have abundant solar energy, are relatively benign thermally (when compared with equatorial regions), and are close to permanently shadowed regions that may contain water ice.