SNARE VTI13 plays a unique role in endosomal trafficking pathways associated with the vacuole and is essential for cell wall organization and root hair growth in arabidopsis

Background and Aims: Root hairs are responsible for water and nutrient uptake from the soil and their growth is responsive to biotic and abiotic changes in their environment. Root hair expansion is a polarized process requiring secretory and endosomal pathways that deliver and recycle plasma membrane and cell wall material to the growing root hair tip. In this paper, the role of VTI13 (AT3G29100), a member of the VTI vesicular soluble NSF attachment receptor (SNARE) gene family in Arabidopsis thaliana, in root hair growth is described.<p></p> Methods: Genetic analysis and complementation of the vti13 root hair phenotypes of Arabidopsis thaliana were first used to assess the role of VTI13 in root hair growth. Transgenic lines expressing a green fluorescent protein (GFP)–VTI13 construct were used to characterize the intracellular localization of VTI13 in root hairs using confocal microscopy and immunotransmission electron microscopy.<p></p> Key Results: VTI13 was characterized and genetic analysis used to show that its function is required for root hair growth. Expression of a GFP–VTI13 fusion in the vti13 mutant background was shown to complement the vti13 root hair phenotype. GFP–VTI13 localized to both the vacuole membrane and a mobile endosomal compartment. The function of VTI13 was also required for the localization of SYP41 to the trans-Golgi network. Immunohistochemical analysis indicated that cell wall organization is altered in vti13 root hairs and root epidermal cells.<p></p> Conclusions: These results show that VTI13 plays a unique role in endosomal trafficking pathways associated with the vacuole within root hairs and is essential for the maintenance of cell wall organization and root hair growth in arabidopsis

The star formation histories of early-type galaxies: insights from the rest-frame ultra-violet

Our current understanding of the star formation histories of early-type galaxies is reviewed, in the context of recent observational studies of their ultra-violet (UV) properties. Combination of UV and optical spectro-photometric data indicates that the bulk of the stellar mass in the early-type population forms at high redshift (z > 2), typically over short timescales (< 1 Gyr). Nevertheless, early-types of all luminosities form stars over the lifetime of the Universe, with most luminous (-23 < M(V) < -21) systems forming 10-15% of their stellar mass after z = 1 (with a scatter to higher value), while their less luminous (M(V) > -21) counterparts form 30-60% of their mass in the same redshift range. The large scatter in the (rest-frame) UV colours in the redshift range 0 < z < 0.7 indicates widespread low-level star formation in the early-type population over the last 8 billion years. The mass fraction of young (< 1 Gyr old) stars in luminous early-type galaxies varies between 1% and 6% at z~0 and is in the range 5-13% at z~0.7. The intensity of recent star formation and the bulk of the UV colour distribution is consistent with what might be expected from minor mergers (mass ratios < 1:6) in an LCDM cosmology.Comment: Brief Review, Mod. Phys. Lett.

Negative thermal expansion in the Prussian Blue analog Zn3[Fe(CN)6]2: X-ray diffraction and neutron vibrational studies

The cubic Prussian Blue (PB) analog, Zn3 [Fe(CN)6]2, has been studied by X-ray powder diffraction and inelastic neutron scattering (INS). X-ray data collected at 300 and 84 K revealed negative thermal expansion (NTE) behaviour for this material. The NTE coefficient was found to be -31.1 x 10-6 K-1. The neutron vibrational spectrum for Zn3[Fe(CN)6]2.xH2O, was studied in detail. The INS spectrum showed well-defined, well-separated bands corresponding to the stretching of and deformation modes of the Fe and Zn octahedra, all below 800 cm-1.Comment: 4 pages, 3 figure

Dynamical quantum phase transition of a two-component Bose-Einstein condensate in an optical lattice

We study dynamics of a two-component Bose-Einstein condensate where the two components are coupled via an optical lattice. In particular, we focus on the dynamics as one drives the system through a critical point of a first order phase transition characterized by a jump in the internal populations. Solving the time-dependent Gross-Pitaevskii equation, we analyze; breakdown of adiabaticity, impact of non-linear atom-atom scattering, and the role of a harmonic trapping potential. Our findings demonstrate that the phase transition is resilient to both contact interaction between atoms and external trapping confinement.Comment: 8 pages, 8 figure

Gravitational radiation timescales for extreme mass ratio inspirals

The capture and inspiral of compact stellar masses into massive black holes is an important source of low-frequency gravitational waves (with frequencies of ~1-100mHz), such as those that might be detected by the planned Laser Interferometer Space Antenna (LISA). Simulations of stellar clusters designed to study this problem typically rely on simple treatments of the black hole encounter which neglect some important features of orbits around black holes, such as the minimum radii of stable, non-plunging orbits. Incorporating an accurate representation of the orbital dynamics near a black hole has been avoided due to the large computational overhead. This paper provides new, more accurate, expressions for the energy and angular momentum lost by a compact object during a parabolic encounter with a non-spinning black hole, and the subsequent inspiral lifetime. These results improve on the Keplerian expressions which are now commonly used and will allow efficient computational simulations to be performed that account for the relativistic nature of the spacetime around the central black hole in the system.Comment: 19 pages, 4 figures. Changed in response to referee's report. Accepted for publication in Astrophysical Journa

Air data position-error calibration using state reconstruction techniques

During the highly maneuverable aircraft technology (HiMAT) flight test program recently completed at NASA Ames Research Center's Dryden Flight Research Facility, numerous problems were experienced in airspeed calibration. This necessitated the use of state reconstruction techniques to arrive at a position-error calibration. For the HiMAT aircraft, most of the calibration effort was expended on flights in which the air data pressure transducers were not performing accurately. Following discovery of this problem, the air data transducers of both aircraft were wrapped in heater blankets to correct the problem. Additional calibration flights were performed, and from the resulting data a satisfactory position-error calibration was obtained. This calibration and data obtained before installation of the heater blankets were used to develop an alternate calibration method. The alternate approach took advantage of high-quality inertial data that was readily available. A linearized Kalman filter (LKF) was used to reconstruct the aircraft's wind-relative trajectory; the trajectory was then used to separate transducer measurement errors from the aircraft position error. This calibration method is accurate and inexpensive. The LKF technique has an inherent advantage of requiring that no flight maneuvers be specially designed for airspeed calibrations. It is of particular use when the measurements of the wind-relative quantities are suspected to have transducer-related errors

Using monoclonal antibodies to label living root hairs: a novel tool for studying cell wall microarchitecture and dynamics in <i>Arabidopsis</i>

Background&lt;p&gt;&lt;/p&gt; The Arabidopsis root hair represents a valuable cell model for elucidating polar expansion mechanisms in plant cells and the overall biology of roots. The deposition and development of the cell wall is central to the root hair expansion apparatus. During this process, incorporation of specific wall polymers into the growing wall architecture constitutes a critical spatio-temporal event that controls hair size and growth rate and one that is closely coordinated with the cell’s endomembrane, cytoskeletal and signal transduction apparatuses.&lt;p&gt;&lt;/p&gt; Results&lt;p&gt;&lt;/p&gt; In this study, the protocol for live cell labeling of roots with monoclonal antibodies that bind to specific wall polymers is presented. This method allows for rapid assessment of root hair cell wall composition during development and assists in describing changes to cell wall composition in transgenic mutant lines. Enzymatic “unmasking” of specific polymers prior to labeling allows for refined interpretation of cell wall chemistry. Live cell immunofluorescence data may also be correlated with transmission electron microscopy-based immunogold labeling.&lt;p&gt;&lt;/p&gt; Conclusions&lt;p&gt;&lt;/p&gt; Live Arabidopsis root hairs may be labeled with cell wall polymer-specific antibodies. This methodology allows for direct visualization of cell wall dynamics throughout development in stable transgenic plant lines. It also provides an important new tool in the elucidation of the specific interactions occurring between membrane trafficking networks, cytoskeleton and the cell wall deposition/remodeling mechanism