We report the polarized reflectance and optical conductivity of the quasi-one-dimensional conductor Li 0.9 Mo 6 O 17 as a function of temperature. The compound displays an unusual ͑non-Drude-type͒ mobile carrier response at low-energy, with partially screened vibrational features along the highly conducting b axis. In addition, we observe Mo d→d transitions near 0.42, 0.57, and 1.3 eV, and an O p→Mo d charge-transfer band near 4 eV. Perpendicular to the b axis, Li 0.9 Mo 6 O 17 exhibits semiconducting behavior with an optical gap of 0.4 eV and electronic structure similar to that of the b axis at higher energies. The substantial temperature dependence of the vibrational modes in this direction reveals that the lattice of Li 0.9 Mo 6 O 17 is not rigid. However, no noticeable change in the lattice through the 25 K metal-insulator transition is observed. Comparing x-ray and infrared data for several model materials, we establish an upper bound on the size of any lattice distortion in Li 0.9 Mo 6 O 17. Based upon these combined results, we argue that localization effects dominate the bulk and microscopic properties of this material.

We measured the optical properties of mixed-valent vanadium oxide nanotubes to investigate the charge degrees of freedom in these novel materials. The electronic structure strongly resembles that of other bulk, low-dimensional, and molecular vanadates. The 1.2-eV band is assigned as a superposition of V 4+ d f d and V 4+ f V 5+ charge-transfer excitations, and the features above 3 eV are attributed to O 2p f V 3d charge-transfer excitations. The 5-eV excitation shows a modest sheet distance dependence, red-shifting with increasing sheet distance. We find that the optical gap is ∼0.56 eV at room temperature and ∼0.65 eV at 4.2 K. It does not depend systematically on tube size. At the same time, selected V-O-V stretching modes sharpen and red-shift with increasing sheet distance. We attribute these trends to the microscopic manifestations of strain, which changes with curvature. A lowfrequency mode is observed at 113 cm -1 , which is assigned as the radial breathing mode of the VO x nanotubes.

1-Aminocyclopropane-1-carboxylic acid (ACC), a biosynthetic precursor of ethylene, has long been proposed to act as a mobile messenger in higher plants. However, little is known about the transport system of ACC. Recently, our genetic characterization of an ACC-resistant mutant with normal ethylene sensitivity revealed that lysine histidine transporter 1 (LHT1) functions as a transporter of ACC. As amino acid transporters might have broad substrate specificity, we hypothesized that other amino acid transporters including LHT1 paralogs might have the ACC-transporter activity. Here, we took a gain-of-function approach by transgenic complementation of lht1 mutant with a selected set of amino acid transporters. When we introduced transgene into the lht1 mutant, the transgenic expression of LHT2, but not of LHT3 or amino acid permease 5 (AAP5), restored the ACC resistance phenotype of the lht1 mutant. The result provides genetic evidence that some, if not all, amino acid transporters in Arabidopsis can function as ACC transporters. In support, when expressed in Xenopus laevis oocytes, both LHT1 and LHT2 exhibited ACC-transporting activity, inducing inward current upon addition of ACC. Interestingly, the transgenic expression of LHT2, but not of LHT3 or AAP5, could also suppress the early senescence phenotypes of the lht1 mutant. Taking together, we propose that plants have evolved a multitude of ACC transporters based on amino acid transporters, which would contribute to the differential distribution of ACC under various spatiotemporal contexts.

A missense mutation of KARRIKIN-INSENSITIVE2, KAI2ply2, compromises its ligand-binding activity, which subsequently impairs KAI2-signaling and multiple aspects of light-dependent responses.

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