810 research outputs found
Susceptibility to ergot in Zimbabwe of sorghums tbat remained uninfected in their native climates in Ethiopia and Rwanda
Forty-four local Ethiopian and Rwandan sorghums (Sorghum bicolor) were observed to remain free of
ergot, or had only low incidence, in their natural equatorial latitudes and were potentially of interest, in
the design of male-sterile lines for F| hybrid breeding, if they possessed a physiologically based resistance
mechanism. These sorghums were therefore also investigated under natural and artificial disease
pressures in Zimbabwe where unadapted development and inappropriate long daylengtb prevented
flowering in 18 accessions. Of the remaining 16 Ethiopian and 10 Rwandan accessions which flowered,
only one from each country remained free of ergot. The susceptibility expressed was ascribed to observed
asynchrony of stigma exsertion with anthesis. In the Rwandan accession that persistently remained free
of ergot in Zimbabwe, histology of ovules showed pollination before floret gaping, so that a general
principle of disease escape due to efficient pollination is proposed for the Ethiopian and Rwandan
sorghums in their native climates. The findings emphasize that cleistogamy is a desirable character for
avoiding ergot infection in self-fertile sorghums and suggest that the Ethiopian and Rwandan sorghutns
may not generally be useful for breeding ergot-resistant male-sterile female lines. However, a few
accessions deserve more detailed study as a potential genetic resource, before a firm conclusion that all
apparent resistance is disease escape owing to efficient pollination
In vivo imaging with a cell-permeable porphyrin-based MRI contrast agent
Magnetic resonance imaging (MRI) with molecular probes offers the potential to monitor physiological parameters with comparatively high spatial and temporal resolution in living subjects. For detection of intracellular analytes, construction of cell-permeable imaging agents remains a challenge. Here we show that a porphyrin-based MRI molecular imaging agent, Mn-(DPA-C[subscript 2])[subscript 2]-TPPS[subscript 3], effectively penetrates cells and persistently stains living brain tissue in intracranially injected rats. Chromogenicity of the probe permitted direct visualization of its distribution by histology, in addition to MRI. Distribution was concentrated in cell bodies after hippocampal infusion. Mn-(DPA-C2)2-TPPS3 was designed to sense zinc ions, and contrast enhancement was more pronounced in the hippocampus, a zinc-rich brain region, than in the caudate nucleus, which contains relatively little labile Zn[superscript 2+]. Membrane permeability, optical activity, and high relaxivity of porphyrin-based contrast agents offer exceptional functionality for in vivo imaging.National Institutes of Health (U.S.) (grant DP2-OD2441)United States. Dept. of Defense (grant DAMD17-03-1-0413)National Institutes of Health (U.S.) (grant R01-GM065519
Memory-Constrained Algorithms for Simple Polygons
A constant-workspace algorithm has read-only access to an input array and may
use only O(1) additional words of bits, where is the size of
the input. We assume that a simple -gon is given by the ordered sequence of
its vertices. We show that we can find a triangulation of a plane straight-line
graph in time. We also consider preprocessing a simple polygon for
shortest path queries when the space constraint is relaxed to allow words
of working space. After a preprocessing of time, we are able to solve
shortest path queries between any two points inside the polygon in
time.Comment: Preprint appeared in EuroCG 201
Secondary conidiation of Sphacelia sorghi on sorghum, a novel factor in the epidemiology of ergot disease
Sphacelia sorghi, the ergot pathogen of sorghum in Zimbabwe, causes copious exudation of honeydew containing macroconidia. Within a few days the exudate develops a white crust consisting of a layer of secondary conidia borne above the honeydew surface on a palisade of sterigma-like projecting hyphae which arise from the macroconidia immediately below the honeydew surface. Secondary conidia are windborne, initiate infection and are recognized for the first time to have an important role in the epidemiology of ergot disease of sorghum in Southern Afric
Windborne spread of ergot disease (Claviceps africana) in sorghum A-lines in Zimbabwe
In field trials in Zimbabwe, C. africana spread rapidly through replicated plots of male-sterile sorghum A-lines, from a group of centrally situated, inoculated plants. Prominent secondary conidiation by the pathogen on the surface of exuded honeydew provided airborne spores which were trapped in a Burkard continuous spore trap and showed diurnal peaks in air close to the primary inoculum source. From the rate and pattern of disease spread it is concluded that the characteristic secondary conidia of C. africana were the principal disease agents within the experimental area, and that ergot spread by windborne secondary conidia has significant epidemiological and economic implications for sorghum hybrid breeding in southern Africa
Claviceps africana sp. nov.; the distinctive ergot pathogen of sorghum in Africa
Stromata arising from ergot sclerotia from sorghum in Zimbabwe were different in colour and texture from those of Claviceps sorghi from sorghum in India, compounding other differences in the dynamics of the early stages of parasitism, the sugar composition of honeydew, the quantitative expression of secondary conidiation and the morphology of sclerotia. The distinctive sexual stage forms the basis of describing the African material as a new Claviceps species which also uniquely elaborates a group of dihydrogenated ergot alkaloids that are biosynthetic intermediates leading to the principal product dihydroergosin
Screening of Hydrodynamic Interactions in Semidilute Polymer Solutions: A Computer Simulation Study
We study single-chain motion in semidilute solutions of polymers of length N
= 1000 with excluded-volume and hydrodynamic interactions by a novel algorithm.
The crossover length of the transition from Zimm (short lengths and times) to
Rouse dynamics (larger scales) is proportional to the static screening length.
The crossover time is the corresponding Zimm time. Our data indicate Zimm
behavior at large lengths but short times. There is no hydrodynamic screening
until the chains feel constraints, after which they resist the flow:
"Incomplete screening" occurs in the time domain.Comment: 3 figure
Mode-coupling theory for multiple-time correlation functions of tagged particle densities and dynamical filters designed for glassy systems
The theoretical framework for higher-order correlation functions involving
multiple times and multiple points in a classical, many-body system developed
by Van Zon and Schofield [Phys. Rev. E 65, 011106 (2002)] is extended here to
include tagged particle densities. Such densities have found an intriguing
application as proposed measures of dynamical heterogeneities in structural
glasses. The theoretical formalism is based upon projection operator techniques
which are used to isolate the slow time evolution of dynamical variables by
expanding the slowly-evolving component of arbitrary variables in an infinite
basis composed of the products of slow variables of the system. The resulting
formally exact mode-coupling expressions for multiple-point and multiple-time
correlation functions are made tractable by applying the so-called N-ordering
method. This theory is used to derive for moderate densities the leading mode
coupling expressions for indicators of relaxation type and domain relaxation,
which use dynamical filters that lead to multiple-time correlations of a tagged
particle density. The mode coupling expressions for higher order correlation
functions are also succesfully tested against simulations of a hard sphere
fluid at relatively low density.Comment: 15 pages, 2 figure
Computing a visibility polygon using few variables
We present several algorithms for computing the visibility polygon of a
simple polygon from a viewpoint inside the polygon, when the polygon
resides in read-only memory and only few working variables can be used. The
first algorithm uses a constant number of variables, and outputs the vertices
of the visibility polygon in O(n\Rout) time, where \Rout denotes the number
of reflex vertices of that are part of the output. The next two algorithms
use O(\log \Rin) variables, and output the visibility polygon in O(n\log
\Rin) randomized expected time or O(n\log^2 \Rin) deterministic time, where
\Rin is the number of reflex vertices of .Comment: 11 pages. Full version of paper in Proceedings of ISAAC 201
Myeloid-derived suppressor cells inhibit T cell activation through nitrating LCK in mouse cancers
Potent immunosuppressive mechanisms within the tumor microenvironment contribute to the resistance of aggressive human cancers to immune checkpoint blockade (ICB) therapy. One of the main mechanisms for myeloid-derived suppressor cells (MDSCs) to induce T cell tolerance is through secretion of reactive nitrogen species (RNS), which nitrates tyrosine residues in proteins involved in T cell function. However, so far very few nitrated proteins have been identified. Here, using a transgenic mouse model of prostate cancer and a syngeneic cell line model of lung cancer, we applied a nitroproteomic approach based on chemical derivation of 3-nitrotyrosine and identified that lymphocyte-specific protein tyrosine kinase (LCK), an initiating tyrosine kinase in the T cell receptor signaling cascade, is nitrated at Tyr394 by MDSCs. LCK nitration inhibits T cell activation, leading to reduced interleukin 2 (IL2) production and proliferation. In human T cells with defective endogenous LCK, wild type, but not nitrated LCK, rescues IL2 production. In the mouse model of castration-resistant prostate cancer (CRPC) by prostate-specific deletion of Pten, p53, and Smad4, CRPC is resistant to an ICB therapy composed of antiprogrammed cell death 1 (PD1) and anticytotoxic-T lymphocyte-associated protein 4 (CTLA4) antibodies. However, we showed that ICB elicits strong anti-CRPC efficacy when combined with an RNS neutralizing agent. Together, these data identify a previously unknown mechanism of T cell inactivation by MDSC-induced protein nitration and illuminate a clinical path hypothesis for combining ICB with RNS-reducing agents in the treatment of CRPC
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