Ultrafast Electron-Electron Scattering in Metallic Phase of 2H-NbSe_{2} Probed by High Harmonic Generation.

Electron-electron scattering on the order of a few to tens of femtoseconds plays a crucial role in the ultrafast electron dynamics of conventional metals. When mid-infrared light is used for driving and the period of light field is comparable to the scattering time in metals, unique light-driven states and nonlinear optical responses associated with the scattering process are expected to occur. Here, we use high-harmonics spectroscopy to investigate the effect of electron-electron scattering on the electron dynamics in thin film 2H-NbSe_{2} driven by a mid-infrared field. We observed odd-order high harmonics up to 9th order as well as a broadband emission from hot electrons in the energy range from 1.5 to 4.0 eV. The electron-electron scattering time in 2H-NbSe_{2} was estimated from the broadband emission to be almost the same as the period of the mid-infrared light field. A comparison between experimental results and a numerical calculation reveals that competition and cooperation between the driving and scattering enhances the nonperturbative behavior of high harmonics in metals, causing a highly nonequilibrium electronic state corresponding to several thousand Kelvin.

Anomalous in-plane anisotropy of the onset of superconductivity in (TMTSF)2ClO4.

We report the magnetic-field amplitude and field-angle dependence of the superconducting onset temperature Tconset of the organic superconductor (TMTSF)2ClO4 in magnetic fields H accurately aligned to the conductive ab' plane. We revealed that the rapid increase of the onset fields at low temperatures occurs both for H || b' and H || a, irrespective of the carrier confinement. Moreover, in the vicinity of the Pauli-limiting field, we report a shift of a principal axis of the in-plane field-angle dependence of Tconset. This feature may be related to an occurrence of Fulde-Ferrell-Larkin-Ovchinnikov phases.

Isolation and expression analysis of gibberellin 20-oxidase homologous gene in apple.

To characterize the gibberellin (GA) 20-oxidase gene in apple, the genomic and cDNA clone from "Fuji" apple (accession no. AB037114) was isolated. The deduced amino acid sequence of this cDNA showed 71% and 66% identity to those of GA 20-oxidase cloned from French bean and Arabidopsis, respectively. The transcript of this gene was detected mainly in immature seeds between 1-3 months after full bloom. These results suggested that this apple GA 20-oxidase gene might be involved in GA biosynthesis in developing apple seed.

Decreased GA1 content caused by the overexpression of OSH1 is accompanied by suppression of GA 20-oxidase gene expression.

We previously reported that overexpression of the rice homeobox gene OSH1 led to altered morphology and hormone levels in transgenic tobacco (Nicotiana tabacum L.) plants. Among the hormones whose levels were changed, GA1 was dramatically reduced. Here we report the results of our analysis on the regulatory mechanism(s) of OSH1 on GA metabolism. GA53 and GA20, precursors of GA1, were applied separately to transgenic tobacco plants exhibiting severely changed morphology due to overexpression of OSH1. Only treatment with the end product of GA 20-oxidase, GA20, resulted in a striking promotion of stem elongation in transgenic tobacco plants. The internal GA1 and GA20 contents in OSH1-transformed tobacco were dramatically reduced compared with those of wild-type plants, whereas the level of GA19, a mid-product of GA 20-oxidase, was 25% of the wild-type level. We have isolated a cDNA encoding a putative tobacco GA 20-oxidase, which is mainly expressed in vegetative stem tissue. RNA-blot analysis revealed that GA 20-oxidase gene expression was suppressed in stem tissue of OSH1-transformed tobacco plants. Based on these results, we conclude that overexpression of OSH1 causes a reduction of the level of GA1 by suppressing GA 20-oxidase expression.

Alteration of hormone levels in transgenic tobacco plants overexpressing the rice homeobox gene OSH1.

The rice (Oryza sativa L.) homeobox gene OSH1 causes morphological alterations when ectopically expressed in transgenic rice, Arabidopsis thaliana, and tobacco (Nicotiana tabacum L.) and is therefore believed to function as a morphological regulator gene. To determine the relationship between OSH1 expression and morphological alterations, we analyzed the changes in hormone levels in transgenic tobacco plants exhibiting abnormal morphology. Levels of the plant hormones indole-3-acetic acid, abscisic acid, gibberellin (GA), and cytokinin (zeatin and trans-zeatin [Z]) were measured in leaves of OSH1-transformed and wild-type tobacco. Altered plant morphology was found to correlate with changes in hormone levels. The more severe the alteration in phenotype of transgenic tobacco, the greater were the changes in endogenous hormone levels. Overall, GA1 and GA4 levels decreased and abscisic acid levels increased compared with wild-type plants. Moreover, in the transformants, Z (active form of cytokinin) levels were higher and the ratio of Z to Z riboside (inactive form) also increased. When GA3 was supplied to the shoot apex of transformants, internode extension was restored and normal leaf morphology was also partially restored. However, such GA3-treated plants still exhibited some morphological abnormalities compared with wild-type plants. Based on these data, we propose the hypothesis that OSH1 affects plant hormone metabolism either directly or indirectly and thereby causes changes in plant development.

Ectopic expression of a tobacco homeobox gene, NTH15, dramatically alters leaf morphology and hormone levels in transgenic tobacco.

The shoot apical meristem functions to generate the lateral organs of a plant throughout the vegetative and reproductive phases. Homeobox genes play key roles in controlling such developmental programs, but their modes of action have not been well defined. Here we describe isolation and biological functions of a novel tobacco homeobox gene, designated NTH15 (Nicotiana tabacum homeobox 15), from a tobacco shoot apex cDNA library. NTH15 encodes a polypeptide of 342 amino acids, its homeodomain is very similar to the class 1 KNOTTED-type homeodomains. NTH15 mRNA is mainly localized in corpus cells in the tobacco shoot apical meristem, but not in tunica layers nor in differentiated lateral organs. The NTH15 cDNA was fused to the cauliflower mosaic virus 35S promoter and used to generate transgenic tobacco plants. Almost all transgenic tobacco plants showed abnormal leaf and/or flower morphology, and were categorized into three groups depending on severity of the leaf phenotype. In transgenic leaves, drastic decrease of GA1 and increase of cytokinin were observed, while the levels of other phytohormones were only slightly changed. Taken together, our results suggest NTH15 is involved in tobacco morphogenesis and abnormal leaf morphology in transgenic plants results from altered hormone levels.