444 research outputs found
The walls have ears: the role of plant CrRLK1Ls in sensing and transducing extracellular signals
In plants, organ formation and cell elongation require the constant adjustment of the dynamic and adaptable cell wall in response to environmental cues as well as internal regulators, such as light, mechanical stresses, pathogen attacks, phytohormones, and other signaling molecules. The molecular mechanisms that perceive these cues and translate them into cellular responses to maintain integrity and remodelling of the carbohydrate-rich cell wall for the coordination of cell growth are still poorly understood. In the last 3 years, the function of six membrane-localized receptor-like kinases (RLKs) belonging to the CrRLK1L family has been linked to the control of cell elongation in vegetative and reproductive development. Moreover, the presence of putative carbohydrate-binding domains in the extracellular domains of these CrRLK1Ls makes this receptor family an excellent candidate for coordinating cell growth, cell-cell communication, and constant cell wall remodelling during the plant life cycl
Evidence for short range orbital order in paramagnetic insulating (Al,V)_2O_3
The local structure of (Al_0.06V_0.94)_2O_3 in the paramagnetic insulating
(PI) and antiferromagnetically ordered insulating (AFI) phase has been
investigated using hard and soft x-ray absorption techniques. It is shown that:
1) on a local scale, the symmetry of the vanadium sites in both the PI and the
AFI phase is the same; and 2) the vanadium 3d - oxygen 2p hybridization, as
gauged by the oxygen 1s absorption edge, is the same for both phases, but
distinctly different from the paramagnetic metallic phase of pure V_2O_3. These
findings can be understood in the context of a recently proposed model which
relates the long range monoclinic distortion of the antiferromagnetically
ordered state to orbital ordering, if orbital short range order in the PI phase
is assumed. The measured anisotropy of the x-ray absorption spectra is
discussed in relation to spin-polarized density functional calculations.Comment: 8 pages, 5 figure
X-Ray Resonant Scattering as a Direct Probe of Orbital Ordering in Transition-Metal Oxides
X-ray resonant scattering at the K-edge of transition metal oxides is shown
to measure the orbital order parameter, supposed to accompany magnetic ordering
in some cases. Virtual transitions to the 3d-orbitals are quadrupolar in
general. In cases with no inversion symmetry, such as VO, treated in
detail here, a dipole component enhances the resonance. Hence, we argue that
the detailed structure of orbital order in VO is experimentally
accessible.Comment: LaTex using RevTex, 4 pages and two included postscript figure
Conserved Roles of CrRLK1L Receptor-Like Kinases in Cell Expansion and Reproduction from Algae to Angiosperms
Receptor-like kinases (RLKs) are regulators of plant development through allowing cells to sense their extracellular environment. They facilitate detection of local endogenous signals, in addition to external biotic and abiotic stimuli. The Catharanthus roseus RLK1-like (CrRLK1L) protein kinase subfamily, which contains FERONIA, plays a central role in regulating fertilization and in cell expansion mechanisms such as cell elongation and tip growth, as well as having indirect links to plant–pathogen interactions. Several components of CrRLK1L signaling pathways have been identified, including an extracellular ligand, coreceptors, and downstream signaling elements. The presence and abundance of the CrRLK1L proteins in the plant kingdom suggest an origin within the Streptophyta lineage, with a notable increase in prevalence in the seeded land plants. Given the function of the sole CrRLK1L protein in a charophycean alga, the possibility of a conserved role in detection and/or regulation of cell wall integrity throughout the Strephtophytes is discussed. Orthologs of signaling pathway components are also present in extant representatives of non-vascular land plants and early vascular land plants including the liverwort Marchantia polymorpha, the moss Physcomitrella patens and the lycophyte Selaginella moellendorffii. Deciphering the roles in development of the CrRLK1L protein kinases in early diverging land plants will provide insights into their ancestral function, furthering our understanding of this diversified subfamily of receptors in higher plants
Theory for Phase Transitions in Insulating Vanadium Oxide
We show that the recently proposed S=2 bond model with orbital degrees of
freedom for insulating VO not only explains the anomalous magnetic
ordering, but also other mysteries of the magnetic phase transition. The model
contains an additional orbital degree of freedom that exhibits a zero
temperature quantum phase transtion in the Ising universality class.Comment: 5 pages, 2 figure
The local structure of OH species on the V2O3(0 0 0 1) surface: a scanned-energy mode photoelectron diffraction study
Scanned-energy mode photoelectron diffraction (PhD), using O 1s photoemission, together with multiple-scattering simulations, have been used to investigate the structure of the hydroxyl species, OH, adsorbed on a V2O3(0 0 0 1) surface. Surface OH species were obtained by two alternative methods; reaction with molecular water and exposure to atomic H resulted in closely similar PhD spectra. Both qualitative assessment and the results of multiple-scattering calculations are consistent with a model in which only the O atoms of outermost layer of the oxide surface are hydroxylated. These results specifically exclude significant coverage of OH species atop the outermost V atoms, i.e. in vanadyl O atom sites. Ab initio density-functional theory cluster calculations provide partial rationalisation of this result, which is discussed the context of the general understanding of this system
Orbitally Degenerate Spin-1 Model for Insulating V2O3
Motivated by recent neutron, X-ray absorption and resonant scattering
experiments, we revisit the electronic structure of V2O3. We propose a model in
which S=1 V3+ ions are coupled in the vertical V-V pairs forming two-fold
orbitally degenerate configurations with S=2. Ferro-orbital ordering of the V-V
pairs gives a description which is consistent with all experiments in the
antiferromagnetic insulating phase.Comment: 4 pages, including three figure
Green love talks; cell–cell communication during double fertilization in flowering plants
A major breakthrough in understanding double fertilization has been made by high resolution live-imaging. This has helped resolve several disputed issues such as preferential fertilization and polyspermy block. Cumulated information of molecular components involved in double fertilization highlights the importance of cell-cell communication between male and female gametophytes
Electronic Structure and Phase Transition in V2O3: Importance of 3d Spin-Orbit Interaction and Lattice Distortion
The 3d electronic structure and phase transition in pure and Cr doped V2O3
are theoretically investigated in relation to the 3d spin-orbit interaction and
lattice distortion. A model consisting of the nearest-neighbor V ion pair with
full degeneracy of the 3d orbitals is studied within the many-body point of
view. It is shown that each V ion with S=1 spin state has a large orbital
magnetic moment and no orbital ordering occurs in the
antiferromagnetic insulating (AFI) phase. The anomalous resonant Bragg
reflection found in the AFI phase is attributed to the magnetic ordering. In
the AFI and paramagnetic insulating (PI) phases, Jahn-Teller like lattice
instability leads to tilting of the V ion pairs from the corundum c-axis and
this causes large difference in the orbital occupation between the paramagnetic
metal and the insulating phases, which is consistent with linear dichroic V 2p
XAS measurements.
To understand the AFI to PI transition, a model spin Hamiltonian is also
proposed. The transition is found to be simultaneous order-disorder transition
of the magnetic moments and tilting directions of the V ion pairs. Softening of
elastic constant C44 and abrupt change in short range spin correlations
observed at the transition are also explained.Comment: 18 pages, 16 figure
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