266 research outputs found
The mutualistic fungus Piriformospora indica protects barley roots from a loss of antioxidant capacity caused by the necrotrophic pathogen Fusarium culmorum
Fusarium culmorum causes root rot in barley (Hordeum vulgare), resulting in severely reduced plant growth and yield. Pretreatment of roots with chlamydospores of the mutualistic root-colonizing basidiomycete Piriformospora indica (Agaricomycotina) prevented necrotization of root tissues and plant growth retardation commonly associated with Fusarium root rot. Quantification of Fusarium infections with a real-time PCR assay revealed a correlation between root rot symptoms and the relative amount of fungal DNA. Fusarium-infected roots showed reduced levels of ascorbate and glutathione (GSH), along with reduced activities of antioxidant enzymes such as superoxide dismutase (SOD), ascorbate peroxidase (APX), glutathione reductase (GR), dehydroascorbate reductase (DHAR), and monodehydroascorbate reductase (MDHAR). Consistent with this, Fusarium-infected roots showed elevated levels of lipid hydroperoxides and decreased ratios of reduced to oxidized forms of ascorbate and glutathione. In clear contrast, roots treated with P. indica prior to inoculation with F. culmorum showed levels of ascorbate and GSH that were similar to controls. Likewise, lipid peroxidation and the overall reduction in antioxidant enzyme activities were largely attenuated by P. indica in roots challenged by F. culmorum. These results suggest that P. indica protects roots from necrotrophic pathogens at least partly, through activating the plant’s antioxidant capacity
Phase-space dependence of particle-ratio fluctuations in Pb+Pb collisions from 20A to 158A GeV beam energy
A novel approach, the identity method, was used for particle identification
and the study of fluctuations of particle yield ratios in Pb+Pb collisions at
the CERN Super Proton Synchrotron (SPS). This procedure allows to unfold the
moments of the unknown multiplicity distributions of protons (p), kaons (K),
pions () and electrons (e). Using these moments the excitation function of
the fluctuation measure [A,B] was measured, with A and
B denoting different particle types. The obtained energy dependence of
agrees with previously published NA49 results on the related
measure . Moreover, was found to depend
on the phase space coverage for [K,p] and [K,] pairs. This feature most
likely explains the reported differences between measurements of NA49 and those
of STAR in central Au+Au collisions
Inclusive production of charged pions in p+C collisions at 158 GeV/c beam momentum
The production of charged pions in minimum bias p+C interactions is studied
using a sample of 377000 inelastic events obtained with the NA49 detector at
the CERN SPS at 158 GeV/c beam momentum. The data cover a phase space area
ranging from 0 to 1.8 GeV/c in transverse momentum and from -0.1 to 0.5 in
Feynman x. Inclusive invariant cross sections are given on a grid of 270 bins
per charge thus offering for the first time a dense coverage of the projectile
hemisphere and of the cross-over region into the target fragmentation zone.Comment: 31 pages, 30 figures, submitted to European Journal of Physic
Energy dependence of kaon-to-proton ratio fluctuations in central Pb+Pb collisions from = 6.3 to 17.3 GeV
Kaons and protons carry large parts of two conserved quantities, strangeness
and baryon number. It is argued that their correlation and thus also
fluctuations are sensitive to conditions prevailing at the anticipated
parton-hadron phase boundary. Fluctuations of the and
ratios have been measured for the first time by NA49 in central Pb+Pb
collisions at 5 SPS energies between = 6.3 GeV and 17.3 GeV.
Both ratios exhibit a change of sign in , a measure of
non-statistical fluctuations, around = 8 GeV. Below this
energy, is positive, indicating higher fluctuation
compared to a mixed event background sample, while for higher energies,
is negative, indicating correlated emission of kaons
and protons. The results are compared to UrQMD calculations which which give a
good description at the higher SPS energies, but fail to reproduce the
transition to positive values.Comment: 5 pages, 4 figure
Proton -- Lambda Correlations in Central Pb+Pb Collisions at sqrt(s_{NN}) = 17.3 GeV
The momentum correlation between protons and lambda particles emitted from
central Pb+Pb collisions at sqrt(s_{NN}) = 17.3 GeV was studied by the NA49
experiment at the CERN SPS. A clear enhancement is observed for small relative
momenta (q_{inv} < 0.2 GeV). By fitting a theoretical model, which uses the
strong interaction between the proton and the lambda in a given pair, to the
measured data a value for the effective source size is deduced. Assuming a
static Gaussian source distribution we derive an effective radius parameter of
R_G = 3.02 \pm 0.20$(stat.)^{+0.44}_{-0.16}(syst.) fm.Comment: 14 pages, 9 figures, submitted to Phys. Rev.
System-size and centrality dependence of charged kaon and pion production in nucleus-nucleus collisions at 40A GeV and158A GeV beam energy
Measurements of charged pion and kaon production are presented in centrality
selected Pb+Pb collisions at 40A GeV and 158A GeV beam energy as well as in
semi-central C+C and Si+Si interactions at 40A GeV. Transverse mass spectra,
rapidity spectra and total yields are determined as a function of centrality.
The system-size and centrality dependence of relative strangeness production in
nucleus-nucleus collisions at 40A GeV and 158A GeV beam energy are derived from
the data presented here and published data for C+C and Si+Si collisions at 158A
GeV beam energy. At both energies a steep increase with centrality is observed
for small systems followed by a weak rise or even saturation for higher
centralities. This behavior is compared to calculations using transport models
(UrQMD and HSD), a percolation model and the core-corona approach.Comment: 32 pages, 14 figures, 4 tables, typo table II correcte
Centrality dependence of proton and antiproton spectra in Pb+Pb collisions at 40A GeV and 158A GeV measured at the CERN SPS
The yields of (anti-)protons were measured by the NA49 Collaboration in
centrality selected Pb+Pb collisions at 40A GeV and 158A GeV. Particle
identification was obtained in the laboratory momentum range from 5 to 63 GeV/c
by the measurement of the energy loss dE/dx in the TPC detector gas. The
corresponding rapidity coverage extends 1.6 units from mid-rapidity into the
forward hemisphere. Transverse mass spectra, the rapidity dependences of the
average transverse mass, and rapidity density distributions were studied as a
function of collision centrality. The values of the average transverse mass as
well as the midrapidity yields of protons when normalized to the number of
wounded nucleons show only modest centrality dependences. In contrast, the
shape of the rapidity distribution changes significantly with collision
centrality, especially at 40A GeV. The experimental results are compared to
calculations of the HSD and UrQMD transport models.Comment: 25 pages, 12 figures, submitted to PR
Antideuteron and deuteron production in mid-central Pb+Pb collisions at 158 GeV
Production of deuterons and antideuterons was studied by the NA49 experiment
in the 23.5% most central Pb+Pb collisions at the top SPS energy of
=17.3 GeV. Invariant yields for and were measured
as a function of centrality in the center-of-mass rapidity range .
Results for together with previously published
measurements are discussed in the context of the coalescence model. The
coalescence parameters were deduced as a function of transverse momentum
and collision centrality.Comment: 9 figure
Transverse Momentum Fluctuations in Nuclear Collisions at 158 AGeV
Results are presented on event-by-event fluctuations in transverse momentum
of charged particles, produced at forward rapidities in p+p, C+C, Si+Si and
Pb+Pb collisions at 158 AGeV. Three different characteristics are discussed:
the average transverse momentum of the event, the Phi_pT fluctuation measure
and two-particle transverse momentum correlations. In the kinematic region
explored, the dynamical fluctuations are found to be small. However, a
significant system size dependence of Phi_pT is observed, with the largest
value measured in peripheral Pb+Pb interactions. The data are compared with
predictions of several models.Comment: will be submitted to Phys. Rev.
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