609 research outputs found
What Brown saw and you can too
A discussion is given of Robert Brown's original observations of particles
ejected by pollen of the plant \textit{Clarkia pulchella} undergoing what is
now called Brownian motion. We consider the nature of those particles, and how
he misinterpreted the Airy disc of the smallest particles to be universal
organic building blocks. Relevant qualitative and quantitative investigations
with a modern microscope and with a "homemade" single lens microscope similar
to Brown's, are presented.Comment: 14.1 pages, 11 figures, to be published in the American Journal of
Physics. This differs from the previous version only in the web site referred
to in reference 3. Today, this Brownian motion web site was launched, and
http://physerver.hamilton.edu/Research/Brownian/index.html, is now correc
Resolving the Origin of Pseudo-Single Domain Magnetic Behavior
The term âpseudo-single domainâ (PSD) has been used to describe the transitional state in rock magnetism that spans the particle size range between the single domain (SD) and multi-domain (MD) states. The particle size range for the stable SD state in the most commonly occurring terrestrial magnetic mineral, magnetite, is so narrow (~20-75 nm) that it is widely considered that much of the paleomagnetic record of interest is carried by âPSDâ rather than stable SD particles. The PSD concept has, thus, become the dominant explanation for the magnetization associated with a major fraction of particles that record paleomagnetic signals throughout geological time. In this paper, we argue that in contrast to the SD and MD states, the term âPSDâ does not describe the relevant physical processes, which have been documented extensively using three-dimensional micromagnetic modeling, and by parallel research in materials science and solid-state physics. We also argue that features attributed to âPSDâ behavior can be explained by nucleation of a single magnetic vortex immediately above the maximum stable SD transition size. With increasing particle size, multiple vortices, antivortices, and domain walls can nucleate, which produce variable cancellation of magnetic moments and a gradual transition into the MD state. Thus, while the term âPSDâ describes a well-known transitional state, it fails to describe adequately the physics of the relevant processes. We recommend that use of this term should be discontinued in favor of âvortex stateâ, which spans a range of behaviors associated with magnetic vortices
Detection of multiple fluorescent labels using superconducting tunnel junction detectors
Phylogenetic and ecological correlates of pollen morphological diversity in a Neotropical rainforest
Morphology varies enormously across clades, and the morphology of a trait may reflect ecological function or the retention of ancestral features. We examine the tension between ecological and phylogenetic correlates of morphological diversity through a case study of pollen grains produced by angiosperms in Barro Colorado Island, Panama (BCI). Using a molecular phylogeny of 730 taxa, we demonstrate a statistically significant association between morphological and genetic distance for these plants. However, the relationship is nonâlinear, and while close relatives share more morphological features than distant relatives, above a genetic distance of ~ 0.7 increasingly distant relatives are not more divergent in phenotype. The pollen grains of biotically pollinated and abiotically pollinated plants overlap in morphological space, but certain pollen morphotypes and individual morphological traits are unique to these pollination ecologies. Our data show that the pollen grains of biotically pollinated plants are significantly more morphologically diverse than those of abiotically pollinated plants
Climate change impacts on banana yields around the world
This is the author accepted manuscript. The final version is available from Nature Research via the DOI in this r4ecordData availability:
All data used are publicly available and open access. All banana production data
sources are listed in Supplementary Table 1. All climatic and topographic data
sources are listed in the Methods.Nutritional diversity is a key element of food security1,2,3. However, research on the effects of climate change on food security has, thus far, focused on the main food grains4,5,6,7,8, while the responses of other crops, particularly those that play an important role in the developing world, are poorly understood. Bananas are a staple food and a major export commodity for many tropical nations9. Here, we show that for 27 countriesâaccounting for 86% of global dessert banana productionâa changing climate since 1961 has increased annual yields by an average of 1.37âtâhaâ1. Past gains have been largely ubiquitous across the countries assessed and African producers will continue to see yield increases in the future. However, global yield gains could be dampened or disappear, reducing to 0.59âtâhaâ1 and 0.19âtâhaâ1 by 2050 under the climate scenarios for Representative Concentration Pathways 4.5 and 8.5, respectively, driven by declining yields in the largest producers and exporters. By quantifying climate-driven and technology-driven influences on yield, we also identify countries at risk from climate change and those capable of mitigating its effects or capitalizing on its benefits.Biotechnology and Biological Sciences Research Council (BBSRC)European Union Horizon 202
Structural, hystochemical and cytochemical characteristics of the stigma and style in Passiflora edulis f. flavicarpa (Passifloraceae)
New data about the suspensor of succulent angiosperms : ultrastructure and cytochemical study of the embryo-suspensor of Sempervivum arachnoideum L. and Jovibarba sobolifera (Sims) Opiz
The development of the suspensor in two species - Sempervivum arachnoideum and Jovibarba sobolifera - was investigated using cytochemical methods, light and electron microscopy. Cytological processes of differentiation in the embryo-suspensor were compared with the development of embryo-proper. The mature differentiated suspensor consists of a large basal cell and three to four chalazal cells. The basal cell produces haustorial branched invading ovular tissues. The walls of the haustorium and the micropylar part of the basal cell form the wall ingrowths typical for a transfer cells. The ingrowths also partially cover the lateral wall and the chalazal wall separating the basal cell from the other embryo cells. The dense cytoplasm filling the basal cell is rich in: numerous polysomes lying free or covering rough endoplasmic reticulum (RER), active dictyosomes, microtubules, bundles of microfilaments, microbodies, mitochondria, plastids and lipid droplets. Cytochemical tests (including proteins, insoluble polysaccharides and lipids are distributed in the suspensor during different stages of embryo development) showed the presence of high amounts of macromolecules in the suspensor cells, particularly during the globular and heart-shaped phases of embryo development. The protein bodies and lipid droplets are the main storage products in the cells of the embryo-proper. The results of Auramine 0 indicate that a cuticular material is present only on the surface walls of the embryo-proper, but is absent from the suspensor cell wall. The ultrastructural features and cytochemical tests indicate that in the two species - S. arachnoideum and J. sobolifera - the embryo-suspensor is mainly involved in the absorption and transport of metabolites from the ovular tissues to the developing embryo-proper
Comparative morphology of the forewing base articulationin Sternorrhyncha compared with a representative of Fulgoromorpha (Insecta, Hemiptera)
The forewing articulation of single species
from each of the four subgroups of Sternorrhyncha
(Aleyrodomorpha, Aphidomorpha, Coccomorpha, Psyllomorpha)
was examined by optical and scanning electron
microscopy. The species were compared with a species of
Cixiidae (Fulgoromorpha), as an outgroup of Sternorrhyncha.
We present the results of a comparative analysis
of the forewing articulation in these five groups, propose a
standardized terminology and compare our findings with
those previously reported. The wing base of all examined
species is composed of the following structures: anterior
and posterior notal wing process, first, second, and third
axillary sclerites, tegula, and axillary cord. The number of
elements included in the wing base and the surrounding
area is the greatest in Cacopsylla mali, the most complicated
species from Sternorrhyncha. Based on the shape of
axillary sclerites and the number of elements forming the
wing base environment, Orthezia urticae (Coccomorpha)
and Cixius nervosus (Fulgoromorpha) are the most similar.
Among Sternorrhyncha, the most similar axillaries are
those of Aphis fabae and Orthezia urticae, which is congruent
with existing classifications. In this paper we show
that the four groups from Sternorrhyncha exhibit their own
distinct wing base morphology
Analysis of expressed sequence tags generated from full-length enriched cDNA libraries of melon
Abstract Background Melon (Cucumis melo), an economically important vegetable crop, belongs to the Cucurbitaceae family which includes several other important crops such as watermelon, cucumber, and pumpkin. It has served as a model system for sex determination and vascular biology studies. However, genomic resources currently available for melon are limited. Result We constructed eleven full-length enriched and four standard cDNA libraries from fruits, flowers, leaves, roots, cotyledons, and calluses of four different melon genotypes, and generated 71,577 and 22,179 ESTs from full-length enriched and standard cDNA libraries, respectively. These ESTs, together with ~35,000 ESTs available in public domains, were assembled into 24,444 unigenes, which were extensively annotated by comparing their sequences to different protein and functional domain databases, assigning them Gene Ontology (GO) terms, and mapping them onto metabolic pathways. Comparative analysis of melon unigenes and other plant genomes revealed that 75% to 85% of melon unigenes had homologs in other dicot plants, while approximately 70% had homologs in monocot plants. The analysis also identified 6,972 gene families that were conserved across dicot and monocot plants, and 181, 1,192, and 220 gene families specific to fleshy fruit-bearing plants, the Cucurbitaceae family, and melon, respectively. Digital expression analysis identified a total of 175 tissue-specific genes, which provides a valuable gene sequence resource for future genomics and functional studies. Furthermore, we identified 4,068 simple sequence repeats (SSRs) and 3,073 single nucleotide polymorphisms (SNPs) in the melon EST collection. Finally, we obtained a total of 1,382 melon full-length transcripts through the analysis of full-length enriched cDNA clones that were sequenced from both ends. Analysis of these full-length transcripts indicated that sizes of melon 5' and 3' UTRs were similar to those of tomato, but longer than many other dicot plants. Codon usages of melon full-length transcripts were largely similar to those of Arabidopsis coding sequences. Conclusion The collection of melon ESTs generated from full-length enriched and standard cDNA libraries is expected to play significant roles in annotating the melon genome. The ESTs and associated analysis results will be useful resources for gene discovery, functional analysis, marker-assisted breeding of melon and closely related species, comparative genomic studies and for gaining insights into gene expression patterns.This work was supported by Research Grant Award No. IS-4223-09C from BARD, the United States-Israel Binational Agricultural Research and Development Fund, and by SNC Laboratoire ASL, de Ruiter Seeds B.V., Enza Zaden B.V., Gautier Semences S.A., Nunhems B.V., Rijk Zwaan B.V., Sakata Seed Inc, Semillas FitĂł S.A., Seminis Vegetable Seeds Inc, Syngenta Seeds B.V., Takii and Company Ltd, Vilmorin and Cie S.A. and Zeraim Gedera Ltd (all of them as part of the support to ICuGI). CC was supported by CNRS ERL 8196.Peer Reviewe
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