20,638 research outputs found
Studies on Resistance to Vegetative (Vip3A) and Crystal (Cry1A) Insecticidal Toxins of Bacillus thuringiensis in Heliothis virescens (Fabricius)
Bacillus thuringiensis (Bt) toxins expressed in commercial transgenic crop varieties
are all δ-endotoxins (Cry toxins) but the identification of novel vegetative insecticidal
proteins (Vip toxins) has extended the range of insecticidal proteins derived from Bt.
One such Vip toxin, Vip3A, primarily targets the midgut epithelium cells of
susceptible insects as Cry toxins do, although they appear to have different binding
sites. The present study investigated the comparative toxicity of Vip3A, Cry1Ab and
Cry1Ac against Heliothis virescens (tobacco budworm) and the impact of antibiotics
on Bt insecticidal activity. The selection of a resistant Vip3A population led to the
determination of cross-resistance, the genetics of resistance and fitness effects. There
was very little variability in the natural susceptibility to Vip3A, Cry1Ab and Cry1Ac
in the populations tested, although the toxicity of Vip3A was much lower compared to
the Cry1A toxins. A Vip3A resistant population was successfully established within
13 selected generations, with little or no cross-resistance to Cry1Ab or Cry1Ac. The
inheritance of resistance ranged from almost completely recessive to incompletely
dominant with a possible paternal influence, was polygenic and relatively stable.
Vip3A resistance showed a fitness benefit, reduced larval development time, and
fitness costs, including survival to adult eclosion, reduced egg viability and reduced
male mating success. The effects of antibiotics on H. virescens larval susceptibility to
Bt toxins varied depending on antibiotic treatment, the Bt toxin used and the larval
instar tested. Bt cotton expressing both Vip3A and Cry1Ab to provide activity against
a wide range of pest Lepidoptera, including H. virescens, a major cotton pest in the
USA is in the process of commercialisation. The present work will help to support a
suitable insecticide resistance management strategy for continued use of Bt toxin in
transgenic crops
Conflicts among Civilizations: The Influence behind War and Art
Why war or conflicts are fought between civilizations is a subject that could be debated with no end. The complexity of how our species reacts with each other and generates conflict exceeds the limitations of a single concept. There is not one answer to the question, but often the combination of the need for economic and political authority along with the thrill of victory, power, and nationalism joining together to create the motivation to fight and conquer
Making the H-Cluster from Scratch
Spectroscopic data begin to elucidate the initial steps in the biosynthesis of the hydrogenase active site.
[Also see Report by
Kuchenreuther
et al.
]
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High resolution spectroscopy in the microwave and far infrared
High resolution rotational spectroscopy has long been central to remote sensing techniques in atmospheric sciences and astronomy. As such, laboratory measurements must supply the required data to make direct interpretation of data for instruments which sense atmospheres using rotational spectra. Spectral measurements in the microwave and far infrared regions are also very powerful tools when combined with infrared measurements for characterizing the rotational structure of vibrational spectra. In the past decade new techniques were developed which have pushed high resolution spectroscopy into the wavelength region between 25 micrometers and 2 mm. Techniques to be described include: (1) harmonic generation of microwave sources, (2) infrared laser difference frequency generation, (3) laser sideband generation, and (4) ultrahigh resolution interferometers
Explicit Construction of Self-Dual Integral Normal Bases for the Square-Root of the Inverse Different
Let be a finite extension of \Q_p, let be a finite abelian Galois
extension of odd degree and let \bo_L be the valuation ring of . We define
to be the unique fractional \bo_L-ideal with square equal to the
inverse different of . For an odd prime and L/\Q_p contained in
certain cyclotomic extensions, Erez has described integral normal bases for
A_{L/\Q_p} that are self-dual with respect to the trace form. Assuming
K/\Q_p to be unramified we generate odd abelian weakly ramified extensions of
using Lubin-Tate formal groups. We then use Dwork's exponential power
series to explicitly construct self-dual integral normal bases for the
square-root of the inverse different in these extensions
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