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The pollen tube clear zone: Clues to the mechanism of polarized growth

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Journal of Integrative Plant Biology 2015年第1期57卷 79-92页

作者： Peter K.Hepler lawrence J.Winship Biology Department University of Massachusetts School of Natural Science Hampshire College

Pollen tubes usually exhibit a prominent region at their apex called the ＂clear zone＂ because it lacks light refracting amyloplasts. A robust, long clear zone often associates with fast growing pollen tubes, and thus serves as an indicator of pollen tube health. Nevertheless we do not understand how it arises or how it is maintained. Here we review the structure of the clear zone, and attempt to explain the factors that contribute to its formation. While amyloplasts and vacuolar elements are excluded from the clear zone, virtually all other organelles are present including secretory vesicles, mitochondria, Golgi dictyosomes, and the endoplas-mic reticulum （ER）. Secretory vesicles aggregate into an inverted cone appressed against the apical plasma membrane. ER elements move nearly to the extreme apex, whereas mitochondria and Golgi dictyosomes move less far forward. The cortical actin fringe assumes a central position in the control of clear zone formation and maintenance, given its role in generating cytoplasmic streaming. Other likely factors include the tip-focused calcium gradient, the apical pH gradient, the influx of water, and a host of signaling factors （small G-proteins）. We think that the clear zone is an emergent property that depends on the interaction of several factors crucial for polarized growth.

关键词： Actin endoplasmic reticulum myosin polarized growth pollen tube

Calcium at the Cell Wall-Cytoplast Interface

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Journal of Integrative Plant Biology 2010年第2期52卷 147-160页

作者： Peter K.Hepler lawrence J.Winship Department of Biology University of MassachusettsAmherstMA 01003USA School of Natural Science Hampshire CollegeAmherstMA 01002USA

Attention is given to the role of Ca^2＋ at the interface between the cell wall and the cytoplast, especially as seen in pollen tubes. While the cytoplasm directs the synthesis and deposition of the wall, it is less well appreciated that the wall exerts considerable self control and influences activities of the cytoplasm. Ca^2＋ participates as a crucial factor in this two way communication. In the cytoplasm, a [Ca^2＋] above 0.1 μM, regulates myriad processes, including secretion of cell wall components. In the cell wall Ca^2＋ , at 10μM to 10 mM, binds negative charges on pectins and imparts structural rigidity to the wall. The plasma membrane occupies a pivotal position between these two compartments, where selective channels regulate influx of Ca^2＋ , and specific carriers pump the ion back into the wall. In addition we draw attention to different factors, which either respond to the wall or are present in the wall, and usually generate elevated[Ca^2＋ ] in the cytoplasm. These factors include：（i） stretch activated channels; （ii） calmodulin; （iii） annexins; （iv） wall associated kinases; （v） oligogalacturonides; and （vi） extracellular adenosine 5＇-triphosphate. Together they provide evidence for a rich and multifaceted system of communication between the cytoplast and cell wall, with Ca^2＋ as a carrier of information.

关键词： Calcium at the Cell Wall-Cytoplast Interface CNGC

Paleosols of the upper Paleozoic Sangre de Cristo Formation,north-central New Mexico:Record of early Permian palaeoclimate in tropical Pangaea

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Journal of Palaeogeography 2017年第2期6卷 144-161页

作者： lawrence H. Tanner Spencer G. Lucas Department of Biological Sciences Le Moyne CollegeSyracuseNY 13214USA New Mexico Museum of Natural History 1801 Mountain Road N.W.AlbuquerqueNM 87014USA

The lower Permian(Wolfcampian) Sangre de Cristo Formation of northern New Mexico consists of silty mudstones and laterally discontinuous sandstones deposited on an aggrading alluvial ***,mudstones display a variety of pedogenic *** mudstone fabrics vary from platy to prismatic;some beds display prominent pedogenic ***-colored root traces are common throughout the section,as are calcareous nodules,which vary from small bodies with diffuse boundaries to vertically stacked,discrete,cm-scale nodules(rhizocretions),and less commonly form coalescing *** occur only in the lower portion of the ca.90-m measured *** of the mudstone beds contain calcretes that are immature(calcic Protosols to calcic Argillisols),but the lower to middle portion of the section also contains mature calcrete horizons(argillic Calcisols and Calcisols).Intercalated micritic limestone beds with sharp contacts containing root traces,are of laterally variable thickness and grade to nodular *** are interpreted as floodplain pond carbonates that have undergone pedogenic alteration(palustrine limestones),indicating long periods of exposure under strongly seasonal climatic *** isotopic composition of the pedogenic carbonate displays a substantial range of values,but most of the range of variation in isotopic composition is accounted for by isotopically heavier carbonate(both carbon and oxygen) precipitated in shallow ponds subject to intense pedogenic reworking(palustrine carbonate).During the early Permian,northern New Mexico was situated in a near equatorial position(ca.4° N).The overall character of the paleosols suggests a persistent warm,semi-humid,seasonal climate throughout most of the interval of deposition during the Wolfcampian,but with episodically increased aridity during formation of the more mature *** long-term trend of climate change is evident in the stratigraphic section examined for this study.

关键词： Sangre de Cristo Formation Wolfcampian Vertisol Argillisol Calcisol Protosol

Successional trends and processes on a glacial foreland in Southern Iceland studied by repeated species counts

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Ecological Processes 2019年第1期8卷 138-148页

作者： Taylor G.Glausen lawrence H.Tanner Jacobs School of Medicine and Biomedical Sciences State University of New York at BuffaloBuffaloNY 14203USA Department of Biological and Environmental Sciences Le Moyne CollegeSyracuseNY 13214USA

Introduction:Primary succession on glacial forelands is increasingly relevant as rapid glacial retreat is exposing growing land areas to plant *** investigated temporal trends,controls,and outcomes in floral succession on a subarctic glacial ***,we examined changes in community composition(mosses,low shrubs,forbs,trees,and graminoids)over long-term(decadal)and short-term(<10 years)scales and attempted to identify the underlying processes responsible for the observed successional ***:The study area was the foreland of the Skaftafellsjӧkull,located in Vatnajӧkull National Park near the south coast of *** established nine transect lines at varying distances from the ice front representing surfaces of age ranging from less than one decade to over 100 *** transect consisted of five measurement stations of 1 m2 where we measured vegetative cover(VC),species richness(SR),and species density(SD)and calculated species evenness(SE).Measurements were made initially in 2007 and repeated at the same geographic coordinates in ***:VC increased with distance from the ice front from 16%to over 90%.SR and SD increased from the youngest pioneer community through a mid-successional stage corresponding to an age of over 60 but less than 100 *** VC but declining SR,SD,and SE characterized the oldest(over 100 years)bryophyte-dominated *** turnover,which involved forbs almost exclusively,increased moderately from early through midsuccessional sites and declined on older *** of the measurements made in 2014 to those made in 2007 demonstrates increased SR at mid-successional sites while SD remained relatively ***:At a small scale,colonization is controlled by local factors such as microtopography and aspect,particularly in proximity to the *** the landscape level,changes in VC and community structure are controlled by time and nutrient *** nutrient level

关键词： Primary succession Glacial foreland Species richness Species density Bryophyte

End-Triassic nonmarine biotic events

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Journal of Palaeogeography 2015年第4期4卷 331-348页

作者： Spencer G.Lucas lawrence H.Tanner New Mexico Museum of Natural History Department of Biological Sciences Le Moyne College

The Late Triassic was a prolonged interval of elevated extinction rates and low origination rates that manifested themselves in a series of extinctions during Carnian, Norian and Rhaetian time. Most of these extinctions took place in the marine realm, particularly affecting radiolarians, conodonts, bivalves, ammonoids and reef-building organisms. On land, the case for a Late Triassic mass extinction is much more tenuous and has largely focused on tetrapod vertebrates（amphibians and reptiles）, though some workers advocate a sudden endTriassic（TJB） extinction of land plants. Nevertheless, an extensive literature does not identify a major extinction of land plants at the TJB, and a comprehensive review of palynological records concluded that TJB vegetation changes were non-uniform（different changes in different places）, not synchronous and not indicative of a mass extinction of land plants. Claims of a substantial perturbation of plant ecology and diversity at the TJB in East Greenland are indicative of a local change in the paleoflora largely driven by lithofacies changes resulting in changing taphonomic filters. Plant extinctions at the TJB were palaeogeographically localized events, not global in extent. With new and more detailed stratigraphic data, the perceived TJB tetrapod extinction is mostly an artifact of coarse temporal resolution, the compiled correlation effect. The amphibian, archosaur and synapsid extinctions of the Late Triassic are not concentrated at the TJB, but instead occur stepwise, beginning in the Norian and extending into the Hettangian. There was a disruption of the terrestrial ecosystem across the TJB, but it was more modest than generally claimed. The ecological severity of the end-Triassic nonmarine biotic events are relatively low on the global scale. Biotic turnover at the end of the Triassic was likely driven by the CAMP（Central Atlantic Magmatic Province） eruptions, which caused significant environmental perturbations（cooling, warming,

关键词： Triassic-Jurassic boundary mass extinction land plants East Greenland tetrapods Newark Supergroup CAMP volcanism

NEW MURID RODENTS FROM THE LATE CENOZOIC OF YUSHE BASIN, SHANXI

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古脊椎动物学报(中英文） 1992年第1期 29-38+87-88页

作者： lawrence J.Flynn Harvard University NY Research Associate American Museum of Natural History and Peabody Museum

As scientific collaborators of the Chinese-American joint project "Neogene Rocks and Faunas, Yushe Basin, Shanxi, PRC", the present authors, with William R. Downs, Northern Arizona University, sampled the Yushe microfauna in the fall of 1987 and 1988. The fossil temains were retrieved by surface collection and by wet-sieving bulk quantities of sediment.

关键词： Yushe Basin Late cenozoic murids new taxa

New players in the regulation of ecdysone biosynthesis

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Journal of Genetics and Genomics 2008年第1期35卷 1-10页

作者： Xun Huang James T. Warren lawrence I. Gilbert Laboratory of Molecular and Developmental Biology Institute of Genetics and Developmental Biology Chinese Academy of Sciences Beijing 100101 China Department of Biology University of North Carolina at Chapel Hill Chapel Hill NC 27599-3280 USA

Insect ecdysone steroid hormone regulates major developmental transitions, such as molting and metamorphosis. The production of ecdysone correlates well with the timing of these transitions. Finding out how the ecdysone biosynthesis is regulated is crucial to fully understand these sophisticated developmental switches. Here we summarized recent findings in the regulation of ecdysone biosynthesis from the aspects of cell signaling, key biosynthetic enzymes and substrate cholesterol trafficking.

关键词： ecdysone cholesterol PTTH P450

China, Like the US, Faces Challenges in Achieving Inclusive Growth through Manufacturing

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China & World Economy 2020年第2期28卷 3-17页

作者： Robert Z.lawrence Peterson Institute for International Economics

For more than three decades the goal of becoming "the factory of the world" has been at the core of China s development *** strategy,in combination with high rates of domestic investment and low rates of consumption,has made Chinese production the most manufacturing intensive in the *** as its wages have risen,China's competitiveness in the most labor-intensive manufacturing industries has *** ability to assemble products remains a major source of its exports,but it has also tried to shift toward more sophisticated value-added production *** domestic spending has shifted away from investment toward consumption as citizens'income has *** Americans,Chinese are also spending more on services than on manufactured *** of these changes are fundamentally altering the structure of China s production,reducing the role of manufacturing and increasing the skill levels of workers in *** paper reviews the challenges posed by these developments for China s long-term goal of achieving more inclusive *** presents evidence that the commonly held perceptions that Chinese manufacturing employment growth is robust are *** fact,such growth has peaked and China is now following a pattern of structural change that is typical of a more mature emerging economy,in which the share of employment in manufacturing declines as workers are increasingly employed in services.

关键词： employment inclusive growth inequality labor manufacturing

A convergence analysis for a class of practical variance-reduction stochastic gradient MCMC

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Science China(Information Sciences) 2019年第1期62卷 67-79页

作者： Changyou CHEN Wenlin WANG Yizhe ZHANG Qinliang SU lawrence CARIN Department of Computer Science and Engineering Department of Electrical and Computer Engineering Duke University Microsoft Research School of Data and Computer Science Sun Yat-sen University

Stochastic gradient Markov chain Monte Carlo(SG-MCMC) has been developed as a flexible family of scalable Bayesian sampling algorithms. However, there has been little theoretical analysis of the impact of minibatch size to the algorithm’s convergence rate. In this paper, we prove that at the beginning of an SG-MCMC algorithm, i.e., under limited computational budget/time, a larger minibatch size leads to a faster decrease of the mean squared error bound. The reason for this is due to the prominent noise in small minibatches when calculating stochastic gradients, motivating the necessity of variance reduction in SG-MCMC for practical use. By borrowing ideas from stochastic optimization, we propose a simple and practical variance-reduction technique for SG-MCMC, that is efficient in both computation and *** importantly, we develop the theory to prove that our algorithm induces a faster convergence rate than standard SG-MCMC. A number of large-scale experiments, ranging from Bayesian learning of logistic regression to deep neural networks, validate the theory and demonstrate the superiority of the proposed variance-reduction SG-MCMC framework.

关键词： Markov chain Monte Carlo SG-MCMC variance reduction deep neural networks