Alga-like forms in onverwacht series, South Africa: oldest recognized lifelike forms on Earth

Spheroidal and cupshaped, carbonaceous alga-like bodies, as well as filamentous structures and amorphous carbonaceous matter occur in sedimentary rocks of the Onverwacht Series (Swaziland System) in South Africa. The Onverwacht sediments are older than 3.2 eons, and they are probably the oldest, littlealtered sedimentary rocks on Earth. The basal Onverwacht sediments lie approximately 10,000 meters stratigraphically below the Fig Tree sedimentary rocks, from which similar organic microstructures have been interpreted as alga-like microfossils. The Onverwacht spheroids and filaments are best preserved in black, carbonrich cherts and siliceous argillites interlayered with thick sequences of lavas. These lifelike forms and the associated carbonaceous substances are probably biological in origin. If so, the origins of unicellular life on Earth are buried in older rocks now obliterated by igneous and metamorphic events.     

Drug-induced alterations of cytokeratin organization in cultured epithelial cells

The distribution of keratin intermediate filaments, previously considered static in organization and imperturbable by conventional drugs used to alter the structure and organization of the cytoskeleton, can be altered significantly by treatment with colchicine and cytochalasin D. The loss of microfilaments and microtubules converts the keratin cytoskeleton from a branching, even distribution to a series of starlike structures whose filaments are maintained by multiple membrane attachment sites. These findings provide a means for manipulating cytokeratin organization to investigate the role of keratins in cytoskeletal structure and function.     

Early proterozoic microfossils and penecontemporaneous quartz cementation in the sokoman iron formation, Canada

Early Proterozoic microfossils from the Sokoman Iron Formation, northeastern Canada, are indistinguishable from those of the Gunflint Formation in both morphology and inferred community structure. The contemporaneity of the Sokoman assemblage with the Bitter Springs-like cyanobacteria of the Belcher Supergroup indicates that differences between the two major types of early Proterozoic microbiotas are primarily ecological and not temporal (evolutionary) in nature. In arenaceous iron formations, microfossils are restricted to peloids and are absent from pore-filling silica interpreted as cement. Cemented arenaceous intraclasts indicate that some of the silica was penecontemporaneous, and the abundance of minus-cement porosity in arenaceous iron formations demonstrates that early (pre-compaction) cementation was common.     

Microfossils in Wisconsinan Loess and Till from Western Illinois and Eastern Iowa

Wisconsinan loess from Illinois and Iowa contains a varied assemblage of microfossils including radiolaria, foraminifera, sponge spicules, and opal phytoliths. The foraminifera and radiolaria are derived from Cretaceous rocks occurring on the northern Great Plains. The sponge spicules are from fresh-water sponges living during the epoch of loess deposition. The phytoliths were produced by vegetation growing during deposition. These microfossils are valuable in determining loess and till provenance and in paleoecological reconstruction.     

Microbial polysaccharides template assembly of nanocrystal fibers

Biological systems can produce extraordinary inorganic structures and morphologies. The mechanisms of synthesis are poorly understood but are of great interest for engineering novel materials. We use spectromicroscopy to show that microbially generated submicrometer-diameter iron oxyhydroxide (FeOOH) filaments contain polysaccharides, providing an explanation for the formation of akaganeite pseudo-single crystals with aspect ratios of approximately 1000:1. We infer that the cells extrude the polysaccharide strands to localize FeOOH precipitation in proximity to the cell membrane to harness the proton gradient for energy generation. Characterization of organic compounds with high spatial resolution, correlated with mineralogical information, should improve our understanding of biomineralization mechanisms.     

Conducting carbon wires in ordered, nanometer-sized channels

The encapsulation of graphite-type carbon wires in the regular, 3-nanometer-wide hexagonal channels of the mesoporous host MCM-41 is reported. Acrylonitrile monomers are introduced through vapor or solution transfer and polymerized in the channels with external radical initiators. Pyrolysis of the intrachannel polyacrylonitrile results in filaments whose microwave conductivity is about 10 times that of bulk carbonized polyacrylonitrile. The MCM host plays a key role in ordering the carbon structure, most likely through the parallel alignment of the precursor polymer chains in the channels. The fabrication of stable carbon filaments in ordered, nanometer-sized channels represents an important step toward the development of nanometer electronics.     

The cytochrome P450 superfamily: Key players in plant development and defense

The cytochrome P450(CYP) superfamily is the largest enzymatic protein family in plants, and it also widely exists in mammals, fungi, bacteria, insects and so on. Members of this superfamily are involved in multiple metabolic pathways with distinct and complex functions, playing important roles in a vast array of reactions. As a result, numerous secondary metabolites are synthesized that function as growth and developmental signals or protect plants from various biotic and abiotic stresses. Here, we summarize the characterization of CYPs, as well as their phylogenetic classification. We also focus on recent advances in elucidating the roles of CYPs in mediating plant growth and development as well as biotic and abiotic stresses responses, providing insights into their potential utilization in plant breeding.     

Muscle contraction and free energy transduction in biological systems

Muscle contraction occurs when the actin and myosin filaments in muscle are driven past each other by a cyclic interaction of adenosine triphosphate (ATP) and actin with cross-bridges that extend from myosin. Current biochemical studies suggest that, during each adenosine triphosphatase cycle, the myosin cross-bridge alternates between two main conformations, which differ markedly in their strength of binding to actin and in their overall structure. Binding of ATP to the cross-bridge induces the weak-binding conformation, whereas inorganic phosphate release returns the cross-bridge to the strong-binding conformation. This cross-bridge cycle is similar to the kinetic cycle that drives active transport and illustrates the general principles of free energy transduction by adenosine triphosphatase systems.     

Mitochondrial-satellite and circular DNA filaments in yeast

Mitochondrial DNA of Saccharomyces cerevisiae contains a satellite DNA (density, 1.682) that appears to exist as open-ended filaments at least 5 microns long. DNA from intact cells contains circular filaments whose lengths vary from 0.5 to 7 microns, with a great majority at 1.95 microns. The circular DNA has a density similar to that of the major nuclear peak (1.697). When heat-denatured mitochondrial-satellite DNA is renatured, it cross-links to form a molecule that is larger than the native molecule. The formation of cross-links results in hypersharpening of the density profiles in cesium chloride and also leads to failure to pass Millipore filter paper.     

1400-million-year-old shale-facies microbiota from the lower belt supergroup, montana

Carbonaceous shales of the Middle Proterozoic Newland Limestone, Belt Supergroup, Little Belt Mountains, Montana, contain abundant and well-preserved filamentous and spheroidal microfossils. The filamentous forms, ranging from less than 1 to 12 micrometers in width, are interpreted as representing the preserved sheaths of at least four species of nostocalean cyanophytes. The spheroidal forms, ranging from 15 to 108 micrometers in size, are evidently planktonic forms and are tentatively interpreted as representing the encystment stage of eukaryotic algae. The Newland microbiota is adaptable to petrographic thin-section work, and useful for evaluating the potential of such microfossils for intercontinental biostratigraphic correlation. It is the oldest shale-facies microbiota presently known from North America.     

JAZ蛋白介导的茉莉酸信号传递

当植物受到生物或非生物因素胁迫时,体内会合成茉莉酸类物质,启动自身的防御反应。茉莉酸途径的抑制因子JAZ(Jasmonate ZIM-domain)蛋白近期被确认,该文对JAZ蛋白在茉莉酸信号传递中的作用作一综述。     

Dinoflagellates: fossil motile-stage tests from the upper cretaceous of the northern new jersey coastal plain

Fossil dinoflagellate tests have been considered to represent encysted, nonmotile stages. The discovery of flagellar porelike structures and probable trichocyst pores in the Upper Cretaceous genus Dinogymnium suggests that motile stage tests are also preserved as acid-resistant, organic-walled microfossils.     

gCap39, a calcium ion- and polyphosphoinositide-regulated actin capping protein

The polymerization of actin filaments is involved in growth, movement, and cell division. It has been shown that actin polymerization is controlled by gelsolin, whose interactions with actin are activated by calcium ion (Ca2+) and inhibited by membrane polyphosphoinositides (PPI). A smaller Ca2(+)- and PPI-regulated protein, gCap39, which has 49% sequence identity with gelsolin, has been identified by cDNA cloning and protein purification. Like gelsolin, gCap39 binds to the fast-growing (+) end of actin filaments. However, gCap39 does not sever actin filaments and can respond to Ca2+ and PPI transients independently, under conditions in which gelsolin is ineffective. The coexistence of gCap39 with gelsolin should allow precise regulation of actin assembly at the leading edge of the cell.     

不同尺度下长白山次生杨桦林群落系统发育结构研究

本文研究了长白山5.2 hm2次生杨桦林样地的群落构建机制。以样地内47种胸径≥1 cm的木本植物为研究对象,构建了物种间的系统发育树,并分析了不同空间尺度和不同径级结构下群落的系统发育结构。结果显示,随着空间尺度的增大,群落系统发育结构的发散程度先增大后减小;而随着径级的增加,群落的系统发育结构呈现向发散变化的趋势。这表明竞争排除作用和非生物的筛选作用共同影响群落构建的结果。其中,在较小的尺度上竞争排除作用是决定群落构建的主要因素;而在较大尺度上则是非生物的过滤作用起主要作用。通过对群落系统发育β多样性与空间因子、环境因子进行方差分解,发现环境因子对系统发育β多样性的解释力较强。其中,土壤水分和土壤深度起最重要的作用。      

Conodont pearls?

Conodonts are zoologically enigmatic, toothlike phosphatic microfossils occurring in marine sedimentary rocks ranging in age from Cambrian to Triassic. Dimpled spheres of less than 1 millimeter in diameter are sporadic associates of conodonts and have identical chemical composition and microstructure. Mineralogy, morphology, and occurrence of these spheres suggest that they are pearls secreted by the conodont-bearing animal.     

Cavitands: organic hosts with enforced cavities

Organic hosts are now being designed and synthesized which contain enforced cavities large enough to complex and even surround simple inorganic or organic guest compounds.     

Actin polymerization and ATP hydrolysis

F-actin is the major component of muscle thin filaments and, more generally, of the microfilaments of the dynamic, multifunctional cytoskeletal systems of nonmuscle eukaryotic cells. Polymeric F-actin is formed by reversible noncovalent self-association of monomeric G-actin. To understand the dynamics of microfilament systems in cells, the dynamics of polymerization of pure actin must be understood. The following model has emerged from recent work. During the polymerization process, adenosine 5'-triphosphate (ATP) that is bound to G-actin is hydrolyzed to adenosine 5'-diphosphate (ADP) that is bound to F-actin. The hydrolysis reaction occurs on the F-actin subsequent to the polymerization reaction in two steps: cleavage of ATP followed by the slower release of inorganic phosphate (Pi). As a result, at high rates of filament growth a transient cap of ATP-actin subunits exists at the ends of elongating filaments, and at steady state a stabilizing cap of ADP.Pi-actin subunits exists at the barbed ends of filaments. Cleavage of ATP results in a highly stable filament with bound ADP.Pi, and release of Pi destabilizes the filament. Thus these two steps of the hydrolytic reaction provide potential mechanisms for regulating the monomer-polymer transition.     

Magnetosomes are cell membrane invaginations organized by the actin-like protein MamK

Magnetosomes are membranous bacterial organelles sharing many features of eukaryotic organelles. Using electron cryotomography, we found that magnetosomes are invaginations of the cell membrane flanked by a network of cytoskeletal filaments. The filaments appeared to be composed of MamK, a homolog of the bacterial actin-like protein MreB, which formed filaments in vivo. In a mamK deletion strain, the magnetosome-associated cytoskeleton was absent and individual magnetosomes were no longer organized into chains. Thus, it seems that prokaryotes can use cytoskeletal filaments to position organelles within the cell.     

杜仲叶橡胶丝网络结构的研究

除去非胶成分使纯粹的橡胶丝完全暴露出来，可得到杜仲全叶的胶丝网络体系。通过观察和比较，可见杜仲叶中的胶丝网络结构与叶脉的网络结构完全一致，证明胶丝是叶脉的组成部分。同时观察到杜仲叶缘锯齿的骨架主要由两股胶丝组成，胶丝网络的分枝形式为反向汇集型，叶尖附近的叶缘上排列着发育不平衡的锯齿结构