Comprehensive analysis of the regulatory roles of auxin in early transdifferentiation into xylem cells

Auxin is essential for the formation of the vascular system. We previously reported that a polar auxin transport inhibitor, 1-N-naphthylphthalamic acid (NPA) decreased intracellular auxin levels and prevented tracheary element (TE) differentiation from isolated Zinnia mesophyll cells, but that additional auxin, 1-naphthaleneacetic acid (NAA) overcame this inhibition. To understand the role of auxin in gene regulation during TE differentiation, we performed microarray analysis of genes expressed in NPA-treated cells and NPA-NAA-treated cells. The systematic gene expression analysis revealed that NAA promoted the expression of genes related to auxin signaling and transcription factors that are known to be key regulators of differentiation of procambial and xylem precursor cells. NAA also promoted the expression of genes related to biosynthesis and metabolism of other plant hormones, such as cytokinin, gibberellin and brassinosteroid. Interestingly, detailed analysis showed that NAA rapidly induces the expression of auxin carrier gene homologues. It suggested a positive feedback loop for auxin-regulating vascular differentiation. Based on these results, we discuss the auxin function in early processes of transdifferentiation into TE

The Receptor-Like Kinase SOL2 Mediates CLE Signaling in Arabidopsis

Arabidopsis sol2 mutants showed CLV3 peptide resistance. Twenty-six synthetic CLE peptides were examined in the clv1, clv2 and sol2 mutants. sol2 showed different levels of resistance to the various peptides, and the spectrum of peptide resistance was quite similar to that of clv2. SOL2 encoded a receptor-like kinase protein which is identical to CORYNE (CRN). GeneChip analysis revealed that the expression of several genes was altered in the sol2 root tip. Here, we suggest that SOL2, together with CLV2, plays an important role in the regulation of root meristem development through the CLE signaling pathway

Plant Tissue Cultures

202

Involvement of Phytosulfokine in the Attenuation of Stress Response during the Transdifferentiation of Zinnia Mesophyll Cells into Tracheary Elements1[W][OA]

Phytosulfokine (PSK) is a sulfated peptide hormone required for the proliferation and differentiation of plant cells. Here, we characterize the physiological roles of PSK in transdifferentiation of isolated mesophyll cells of zinnia (Zinnia elegans ‘Canary Bird’) into tracheary elements (TEs). Transcripts for a zinnia PSK precursor gene, ZePSK1, show two peaks of expression during TE differentiation; the first accumulation is transiently induced in response to wounding at 24 h of culture, and the second accumulation is induced in the final stage of TE differentiation and is dependent on endogenous brassinosteroids. Chlorate, a potent inhibitor of peptide sulfation, is successfully applied as an inhibitor of PSK action. Chlorate significantly suppresses TE differentiation. The chlorate-induced suppression of TE differentiation is overcome by exogenously applied PSK. In the presence of chlorate, expression of stress-related genes for proteinase inhibitors and a pathogenesis-related protein is enhanced and changed from a transient to a continuous pattern. On the contrary, administration of PSK significantly reduces the accumulation of transcripts for the stress-related genes. Even in the absence of auxin and cytokinin, addition of PSK suppresses stress-related gene expression. Microarray analysis reveals 66 genes down-regulated and 42 genes up-regulated in the presence of PSK. The large majority of down-regulated genes show significant similarity to various families of stress-related proteins, including chitinases, phenylpropanoid biosynthesis enzymes, 1-aminocyclopropane-1-carboxylic acid synthase, and receptor-like protein kinases. These results suggest the involvement of PSK in the attenuation of stress response and healing of wound-activated cells during the early stage of TE differentiation

Extension of Improved Particle and Energy Confinement Regime in the Core of LHD Plasma

Recent two major topics of Large Helical Device (LHD) towards fusion relevant conditions, high-density operation and high-ion-temperature operation, are reported. Super dense core plasma was obtained by the combination of repetitive hydrogen ice pellet injection and high power neutral beam injection (NBI) heating. A very peaked density profile with the highest central density of 1.1 × 1021 m-3 was produced showing that the particle transport was suppressed very well in the plasma core. The spatial density profile varies as the position of magnetic axis (Rax), and the steepest profile is obtained at Rax = 3.95 m. The highest central ion temperature of 5.6 keV was obtained in hydrogen plasma at electron density of 1.6 × 1019 m-3 by NBI, where a peaked ion-temperature profile with internal ion energy transport barrier was observed. The profile of electron temperature did not change much and was broad even when the ion temperature had a peaked profile. The central ion temperature is higher than the electron temperature, which is a new operation regime of LHD. High central ion temperature accompanied strong toroidal rotation and an extreme hollow profile of carbon ions (impurity hole). These steep temperature profiles were obtained so far at around Rax = 3.6 m. The compatibility between particle and energy confinement is a new issue of LHD to explore a new operation regime for attractive fusion reactor