2,439 research outputs found
The use of metabolomics to dissect plant responses to abiotic stresses
Plant metabolism is perturbed by various abiotic stresses. As such the metabolic network of plants must be reconfigured under stress conditions in order to allow both the maintenance of metabolic homeostasis and the production of compounds that ameliorate the stress. The recent development and adoption of metabolomics and systems biology approaches enable us not only to gain a comprehensive overview, but also a detailed analysis of crucial components of the plant metabolic response to abiotic stresses. In this review we introduce the analytical methods used for plant metabolomics and describe their use in studies related to the metabolic response to water, temperature, light, nutrient limitation, ion and oxidative stresses. Both similarity and specificity of the metabolic responses against diverse abiotic stress are evaluated using data available in the literature. Classically discussed stress compounds such as proline, gamma-amino butyrate and polyamines are reviewed, and the widespread importance of branched chain amino acid metabolism under stress condition is discussed. Finally, where possible, mechanistic insights into metabolic regulatory processes are discussed
Bi-HKT and bi-Kaehler supersymmetric sigma models
We study CKT (or bi-HKT) N = 4 supersymmetric quantum mechanical sigma
models. They are characterized by the usual and the mirror sectors displaying
each HKT geometry. When the metric involves isometries, a Hamiltonian reduction
is possible. The most natural such reduction with respect to a half of bosonic
target space coordinates produces an N = 4 model, related to the twisted
Kaehler model due to Gates, Hull and Rocek, but including certain extra F-terms
in the superfield action.Comment: 31 pages, minor corrections in the published versio
Spin-Echo Measurements for an Anomalous Quantum Phase of 2D Helium-3
Previous heat-capacity measurements of our group had shown the possible
existence of an anomalous quantum phase containing the zero-point vacancies
(ZPVs) in 2D He. The system is monolayer He adsorbed on graphite
preplated with monolayer He at densities () just below the 4/7
commensurate phase (). We carried out
pulsed-NMR measurements in order to examine the microscopic and dynamical
nature of this phase. The measured decay of spin echo signals shows the
non-exponential behaviour. The decay curve can be fitted with the double
exponential function, but the relative intensity of the component with a longer
time constant is small (5%) and does not depend on density and temperature,
which contradicts the macroscopic fluid and 4/7 phase coexistence model. This
slowdown is likely due to the mosaic angle spread of Grafoil substrate and the
anisotropic spin-spin relaxation time in 2D systems with respect to the
magnetic field direction. The inverse value deduced from the major echo
signal with a shorter time constant, which obeys the single exponential
function, decreases linearly with decreasing density from , supporting the
ZPV model.Comment: 4 pages, 6 figure
Monotone independence, comb graphs and Bose-Einstein condensation
The adjacency matrix of a comb graph is decomposed into a sum of monotone independent random variables with respect to the vacuum state. The vacuum spectral distribution is shown to be asymptotically the arcsine law as a consequence of the monotone central limit theorem. As an example the comb lattice is studied with explicit calculation
Localization of the Grover walks on spidernets and free Meixner laws
A spidernet is a graph obtained by adding large cycles to an almost regular
tree and considered as an example having intermediate properties of lattices
and trees in the study of discrete-time quantum walks on graphs. We introduce
the Grover walk on a spidernet and its one-dimensional reduction. We derive an
integral representation of the -step transition amplitude in terms of the
free Meixner law which appears as the spectral distribution. As an application
we determine the class of spidernets which exhibit localization. Our method is
based on quantum probabilistic spectral analysis of graphs.Comment: 32 page
Divergence of the orbital nuclear magnetic relaxation rate in metals
We analyze the nuclear magnetic relaxation rate due to the
coupling of nuclear spin to the orbital moment of itinerant electrons in
metals. In the clean non--interacting case, contributions from large--distance
current fluctuations add up to cause a divergence of . When
impurity scattering is present, the elastic mean free time cuts off the
divergence, and the magnitude of the effect at low temperatures is controlled
by the parameter , where is the chemical potential. The
spin--dipolar hyperfine coupling, while has the same spatial variation
as the orbital hyperfine coupling, does not produce a divergence in the nuclear
magnetic relaxation rate.Comment: 11pages; v4: The analysis of the normal state is more compelete now,
including a comparison with other hyperfine interactions and a detailed
discussion of the effect in representative metals. The superconducting state
is excluded from consideration in this pape
The Momentum Constraints of General Relativity and Spatial Conformal Isometries
Transverse-tracefree (TT-) tensors on , with an
asymptotically flat metric of fast decay at infinity, are studied. When the
source tensor from which these TT tensors are constructed has fast fall-off at
infinity, TT tensors allow a multipole-type expansion. When has no
conformal Killing vectors (CKV's) it is proven that any finite but otherwise
arbitrary set of moments can be realized by a suitable TT tensor. When CKV's
exist there are obstructions -- certain (combinations of) moments have to
vanish -- which we study.Comment: 16 page
Metabolic profiles of six African cultivars of cassava (Manihot esculenta Crantz) highlight bottlenecks of root yield
Open Access Article; Published online: 17 Jan 2020Cassava is an important staple crop in sub‐Saharan Africa, due to its high productivity even on nutrient poor soils. The metabolic characteristics underlying this high productivity are poorly understood including the mode of photosynthesis, reasons for the high rate of photosynthesis, the extent of source/sink limitation, the impact of environment, and the extent of variation between cultivars. Six commercial African cassava cultivars were grown in a greenhouse in Erlangen, Germany, and in the field in Ibadan, Nigeria. Source leaves, sink leaves, stems and storage roots were harvested during storage root bulking and analyzed for sugars, organic acids, amino acids, phosphorylated intermediates, minerals, starch, protein, activities of enzymes in central metabolism and yield traits. High ratios of RuBisCO:phosphoenolpyruvate carboxylase activity support a C3 mode of photosynthesis. The high rate of photosynthesis is likely to be attributed to high activities of enzymes in the Calvin–Benson cycle and pathways for sucrose and starch synthesis. Nevertheless, source limitation is indicated because root yield traits correlated with metabolic traits in leaves rather than in the stem or storage roots. This situation was especially so in greenhouse‐grown plants, where irradiance will have been low. In the field, plants produced more storage roots. This was associated with higher AGPase activity and lower sucrose in the roots, indicating that feedforward loops enhanced sink capacity in the high light and low nitrogen environment in the field. Overall, these results indicated that carbon assimilation rate, the K battery, root starch synthesis, trehalose, and chlorogenic acid accumulation are potential target traits for genetic improvement
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