The cell nucleus communicates with the cytoplasm through a nucleocytoplasmic linker that maintains the shape of the nucleus and mediates its migration. In contrast to animal nuclei, which are moved by motor proteins (kinesins and dyneins) along the microtubule cytoskeleton, plant nuclei move rapidly and farther along an actin filament cytoskeleton. This implies that plants use a distinct nucleocytoplasmic linker for nuclear dynamics, although its molecular identity is unknown. Here, we describe a new type of nucleocytoplasmic linker consisting of a myosin motor and nuclear membrane proteins. In the Arabidopsis thaliana mutant kaku1, nuclear movement was impaired and the nuclear envelope was abnormally invaginated. The responsible gene was identified as myosin XI-i, which encodes a plant-specific myosin. Myosin XI-i is specifically localized on the nuclear membrane, where it physically interacts with the outer-nuclear-membrane proteins WIT1 and WIT2. Both WIT proteins are required for anchoring myosin XI-i to the nuclear membrane and for nuclear movement. A striking feature of plant cells is dark-induced nuclear positioning in mesophyll cells. A deficiency of either myosin XI-i or WIT proteins diminished dark-induced nuclear positioning. The unique nucleocytoplasmic linkage in plants might enable rapid nuclear positioning in response to environmental stimuli.

Plants are able to bend nearly every organ in response to environmental stimuli such as gravity and light(1,2). After this first phase, the responses to stimuli are restrained by an independent mechanism, or even reversed, so that the organ will stop bending and attain its desired posture. This phenomenon of organ straightening has been called autotropism(3) and autostraightening(4) and modelled as proprioception(5). However, the machinery that drives organ straightening and where it occurs are mostly unknown. Here, we show that the straightening of inflorescence stems is regulated by an actin-myosin XI cytoskeleton in specialized immature fibre cells that are parallel to the stem and encircle it in a thin band. Arabidopsis mutants defective in myosin XI (specifically XIf and XIk) or ACTIN8 exhibit hyperbending of stems in response to gravity, an effect independent of the physical properties of the shoots. The actin-myosin XI cytoskeleton enables organs to attain their new position more rapidly than would an oscillating series of diminishing overshoots in environmental stimuli. We propose that the long actin filaments in elongating fibre cells act as a bending tensile sensor to perceive the organ's posture and trigger the straightening system.

Electron cyclotron resonance deposition, structure, and properties of oxygen incorporated hydrogenated diamondlike amorphous carbon films J. Appl. Phys. 96, 5456 (2004); 10.1063/1.1804624Effects of thermal annealing on the structural, mechanical, and tribological properties of hard fluorinated carbon films deposited by plasma enhanced chemical vapor depositionThe effect of annealing in an ultrahigh vacuum on the chemical structure of diamondlike carbon ͑DLC͒ was investigated using photoelectron spectroscopy, thermal desorption spectroscopy, electrical resistivity, and micro-Raman spectroscopy measurements. The line shapes of the C 1s photoelectron spectra depended on annealing temperature. The relative intensities of four chemical components in the spectra were quantitatively evaluated: sp 3 carbon with carbon-carbon bonds ͑C-C sp 3 carbon͒, sp 2 carbon with carbon-carbon bonds ͑C-C sp 2 carbon͒, sp 2 carbon with hydrogen-carbon bonds ͑H-C sp 2 carbon͒, and sp 3 carbon with hydrogen-carbon bonds ͑H-C sp 3 carbon͒. The variation of the ratio of the components demonstrated that hydrogen in DLC is emitted to the outside in between 450 and 600°C, and the remaining DLC is graphized above 600°C. The increase in the asymmetry of the C 1s spectra and the decrease in the electrical resistivity of the DLC film with annealing temperature agree with the picture that the H-C bonds in DLC produces large free spaces in the structure, which inhibit conductive routes and lead to high electrical resistivity.

Angle-resolved x-ray photoelectron spectroscopy was used to investigate the surface of a diamondlike carbon film prepared by the ionized deposition method. We then analyzed the C 1s spectra using the Doniach-Šunjić (DŠ) [J. Phys. C 3, 285 (1970)] function convoluted with a Gaussian function. Consequently, we obtained four fitting curves for the carbon components in each spectrum, regardless of the assumption of the singularity index (α) in the DŠ function, which expresses the asymmetry of the C 1s spectrum. The curves were assigned in the order of binding energy to bulk sp3 carbon (283.7–283.8eV), bulk sp2 carbon (284.2–284.3eV), surface sp2 carbon (284.7–284.8eV), and surface sp3 (285.3–285.4eV) carbon. We further considered the influence of the assumption of α. Consequently, we suggest that the C 1s spectra can be quantitatively analyzed without considering the influences of α when the ratio of α for sp2 carbon to that for sp3 carbon [α(sp2):α(sp3)] is between 10:0 and 5:5. The distribution in the α ratio may indicate that the sp2 and the sp3 carbon atoms can interact with each other (hybridization) and differ from those highly oriented pyrolytic graphite and diamond, respectively.

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