2,261 research outputs found
Coarse woody debris: Managing benefits and fire hazard in the recovering forest
Management of coarse woody debris following fire requires consideration of its positive and negative values. The ecological benefits of coarse woody debris and fire hazard considerations are summarized. This paper presents recommendations for desired ranges of coarse woody debris. Example simulations illustrate changes in debris over time and with varying management
Begomovirus disease complex: emerging threat to vegetable production systems of West and Central Africa
Vegetables play a major role in the livelihoods of the rural poor in Africa. Among major constraints to vegetable
production worldwide are diseases caused by a group of viruses belonging to the genus Begomovirus, family
Geminiviridae. Begomoviruses are plant-infecting viruses, which are transmitted by the whitefly vector Bemisia tabaci
and have been known to cause extreme yield reduction in a number of economically important vegetables around
the world. Several begomoviruses have been detected infecting vegetable crops in West and Central Africa (WCA).
Small single stranded circular molecules, alphasatellites and betasatellites, which are about half the size of their
helper begomovirus genome, have also been detected in plants infected by begomoviruses. In WCA, B. tabaci has
been associated with suspected begomovirus infections in many vegetable crops and weed species. Sequencing of
viral genomes from crops such as okra resulted in the identification of two previously known begomovirus species
(Cotton leaf curl Gezira virus and Okra yellow crinkle virus) as well as a new recombinant begomovirus species (Okra
leaf curl Cameroon virus), a betasatellite (Cotton leaf curl Gezira betasatellite) and new alphasatellites. Tomato and
pepper plants with leaf curling were shown to contain isolates of new begomoviruses, collectively referred to as
West African tomato-infecting begomoviruses (WATIBs), new alphasatellites and betasatellites. To study the potential
of weeds serving as begomovirus reservoirs, begomoviruses and satellites in the weed Ageratum conyzoides were
characterized. Sequence analyses showed that they were infected by isolates of a new begomovirus (Ageratum
leaf curl Cameroon virus) that belong to the WATIBs group, a new betasatellite (Ageratum leaf curl Cameroon
betasatellite), an alphasatellite and two types of defective recombinants between a begomovirus and an alphasatellite.
Putative recombinations were detected in begomovirus genomes for all four plant species studied, indicating that
recombination is an important mechanism for their evolution. A close relationship between the begomoviruses
infecting pepper and tomato and A. conyzoides and the detection of the same alphasatellite in them support the idea
that weeds are important reservoirs for begomoviruses and their satellites. With this high diversity, recombination
potential and transmission by B. tabaci, begomoviruses and ssDNA satellites pose a serious threat to crop production in
West and Central Africa
First report of Soybean chlorotic blotch virus and West African Asystasia virus 1 infecting cassava and a wild cassava relative in Cameroon and Togo
Mechanical heterogeneity in the bone microenvironment as characterised by atomic force microscopy
Bones are structurally heterogeneous organs with diverse functions that undergo mechanical stimuli across multiple length scales. Mechanical characterisation of the bone microenvironment is important for understanding how bones function in health and disease. Here we describe the mechanical architecture of cortical bone, the growth plate, metaphysis and marrow in fresh murine bones, probed using atomic force microscopy in physiological buffer. Both elastic and viscoelastic properties are found to be highly heterogeneous with moduli ranging over 3 to 5 orders of magnitude, both within and across regions. All regions include extremely soft areas, with moduli of a few Pascal and viscosities as low as tens Paâ‹…s. Aging impacts the viscoelasticity of the bone marrow strongly but has limited effect on the other regions studied. Our approach provides the opportunity to explore the mechanical properties of complex tissues at the length scale relevant to cellular processes and how these impact on aging and disease
Neutron Stars in a Varying Speed of Light Theory
We study neutron stars in a varying speed of light (VSL) theory of gravity in
which the local speed of light depends upon the value of a scalar field .
We find that the masses and radii of the stars are strongly dependent on the
strength of the coupling between and the matter field and that for
certain choices of coupling parameters, the maximum neutron star mass can be
arbitrarily small. We also discuss the phenomenon of cosmological evolution of
VSL stars (analogous to the gravitational evolution in scalar-tensor theories)
and we derive a relation showing how the fractional change in the energy of a
star is related to the change in the cosmological value of the scalar field.Comment: 15 pages, 2 figures. Added solutions with a more realistic equation
of state. To be published in PR
The trans-activation domain of the sporulation response regulator Spo0A revealed by X-ray crystallography
Sporulation in Bacillus involves the induction of scores of genes in a temporally and spatially co-ordinated programme of cell development. Its initiation is under the control of an expanded two-component signal transduction system termed a phosphorelay. The master control element in the decision to sporulate is the response regulator, Spo0A, which comprises a receiver or phosphoacceptor domain and an effector or transcription activation domain. The receiver domain of Spo0A shares sequence similarity with numerous response regulators, and its structure has been determined in phosphorylated and unphosphorylated forms. However, the effector domain (C-Spo0A) has no detectable sequence similarity to any other protein, and this lack of structural information is an obstacle to understanding how DNA binding and transcription activation are controlled by phosphorylation in Spo0A. Here, we report the crystal structure of C-Spo0A from Bacillus stearothermophilus revealing a single alpha -helical domain comprising six alpha -helices in an unprecedented fold. The structure contains a helix-turn-helix as part of a three alpha -helical bundle reminiscent of the catabolite gene activator protein (CAP), suggesting a mechanism for DNA binding. The residues implicated in forming the sigma (A)-activating region clearly cluster in a flexible segment of the polypeptide on the opposite side of the structure from that predicted to interact with DNA. The structural results are discussed in the context of the rich array of existing mutational data
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