Crystal structures and transistor properties of phenyl-substituted tetrathiafulvalene derivatives.

The crystal structures, thin-film properties, and field-effect transistor (FET) characteristics of tetrathiafulvalene (TTF) derivatives with two phenyl groups are systematically investigated. The highest mobility, 0.11 cm(2) V(-1) s(-1), is observed in biphenyl-substituted TTF (1). The correlation between the crystal structures and the FET properties demonstrates that good transistor properties are associated with two-dimensional intermolecular interaction, which is achieved when the molecules are standing nearly perpendicular to the substrate. Since these TTF derivatives are strong electron donors, the use of a metallic charge-transfer salt (TTF)(TCNQ) as the source and drain electrodes has resulted in a considerable reduction of the off current (TCNQ: tetracyanoquinodimethane).

Different mechanisms of four aluminum (Al)-resistant transgenes for Al toxicity in Arabidopsis.

We have characterized the mechanism of action of four transgenes (AtBCB [Arabidopsis blue copper-binding protein], parB [tobacco (Nicotiana tabacum) glutathione S-transferase], NtPox [tobacco peroxidase], and NtGDI1 [tobacco GDP dissociation inhibitor]) that independently Al resistance on transgenic Arabidopsis. All four transgenic lines showed lower deposition of callose after Al treatment than the Landsberg erecta ecotype of Arabidopsis, confirming that the four genes function to ameliorate Al toxicity. Influx and efflux experiments of Al ions suggested that the AtBCB gene may suppress Al absorption, whereas expression of the NtGDI1 gene promotes a release of Al in the root tip region of Arabidopsis. The total enzyme activities of glutathione S-transferases or peroxidases in transgenic lines carrying either the parB or NtPox genes were significantly higher than in the Landsberg erecta ecotype of Arabidopsis, and these enzyme activities were maintained at higher levels during Al stress. Furthermore, lipid peroxidation caused by Al stress was repressed in these two transgenic lines, suggesting that overexpression of these two genes diminishes oxidative damage caused by Al stress. Al-treated roots of transgenic plants were also stained by 4',6-diamino-2-phenylindole to monitor cell death caused by Al toxicity. The result suggested that cell death is repressed in the NtPox line. Analysis of F(1) hybrids between the four transgenic lines suggests that more resistant transgenic plants can be constructed by combinations of these four genes.

Expression and stress-dependent induction of potassium channel transcripts in the common ice plant.

We have characterized transcripts for three potassium channel homologs in the AKT/KAT subfamily (Shaker type) from the common ice plant (Mesembryanthemum crystallinum), with a focus on their expression during salt stress (up to 500 mM NaCl). Mkt1 and 2, Arabidopsis AKT homologs, and Kmt1, a KAT homolog, are members of small gene families with two to three isoforms each. Mkt1 is root specific; Mkt2 is found in leaves, flowers, and seed capsules; and Kmt1 is expressed in leaves and seed capsules. Mkt1 is present in all cells of the root, and in leaves a highly conserved isoform is detected present in all cells with highest abundance in the vasculature. MKT1 for which antibodies were made is localized to the plasma membrane. Following salt stress, MKT1 (transcripts and protein) is drastically down-regulated, Mkt2 transcripts do not change significantly, and Kmt1 is strongly and transiently (maximum at 6 h) up-regulated in leaves and stems. The detection and stress-dependent behavior of abundant transcripts representing subfamilies of potassium channels provides information about tissue specificity and the complex regulation of genes encoding potassium uptake systems in a halophytic plant.

Detection and molecular analysis of plant- and insect-associated bacteria harboring aconitate isomerase involved in biosynthesis of trans-aconitic acid as antifeedant in brown planthoppers.

The activity of aconitate isomerase, which is involved in the biosynthesis of trans-aconitic acid as antifeedant in brown planthoppers, was detected in Pseudomonas fluorescens LRB3W1 and Pseudomonas putida MAFF301685 but not in Pseudomonas putida MAFF301684. The enzyme activity was induced in the presence of trans-aconitate, and therefore bacteria showing the enzyme activity were easily detected by their ability to grow on the minimal medium containing trans-aconitate as the sole carbon source (ACO agar medium). Experiments on growth of plant- or insect-associated bacteria on ACO agar medium showed that most of the Gram-negative bacteria displayed the aconitate isomerase activity unlike most of the Gram-positive bacteria isolated mainly from insects. Mini-Tn5 transposon derivatives of P. fluorescens LRB3W1 lacking completely or partially their ability to grow on ACO agar medium were obtained. Southern blot analysis with a mini-Tn5 DNA probe definitely showed that the genes responsible for the biosynthesis of aconitate isomerase present on chromosomal DNA. Thus, it was suggested that genes for aconitate isomerase biosynthesis are commonly present in Gram-negative plant- or insect-associated bacteria, and also the DNA fragments including the genes were detected in P. fluorescens LRB3W1.

A family of transcripts encoding water channel proteins: tissue-specific expression in the common ice plant.

Seawater-strength salt stress of the ice plant (Mesembryanthemum crystallinum) initially results in wilting, but full turgor is restored within approximately 2 days. We are interested in a mechanistic explanation for this behavior and, as a requisite for in-depth biochemical studies, have begun to analyze gene expression changes in roots coincident with the onset of stress. cDNAs that suggested changes in mRNA amount under stress were found; their deduced amino acid sequences share homologies with proteins of the Mip (major intrinsic protein) gene family and potentially encode aquaporins. One transcript, MipB, was found only in root RNA, whereas two other transcripts, MipA and MipC, were detected in roots and leaves. Transcript levels of MipB were of low abundance. All transcripts declined initially during salt stress but later recovered to at least prestress level. The most drastic decline was in MipA and MipC transcripts. MipA mRNA distribution in roots detected by in situ hybridization indicated that the transcript was present in all cells in the root tip. In the expansion zone of the root where vascular bundles differentiate, MipA transcript amounts were most abundant in the endodermis. In older roots, which had undergone secondary growth, MipA was highly expressed in cell layers surrounding individual xylem strands. MipA was also localized in leaf vascular tissue and, in lower amounts, in mesophyll cells. Transcripts for MipB seemed to be present exclusively in the tip of the root, in a zone before and possibly coincident with the development of a vascular system. MipA- and MipB-encoded proteins expressed in Xenopus oocytes led to increased water permeability. mRNA fluctuations of the most highly expressed MipA and MipC coincided with turgor changes in leaves under stress. As the leaves regained turgor, transcript levels of these water channel proteins increased.

ATP-Regulated Ion Channels in the Plasma Membrane of a Characeae Alga, Nitellopsis obtusa.

Using the patch-clamp technique, we recorded single-channel currents across the excised patch of the plasma membrane of Nitellopsis. Both K(+) and Na(+) can pass this channel, but currents were not carried by Cl(-). Upon the addition of ATP or AMP to the cytoplasmic side, the frequency of channel opening decreased. This is the first report on an ATP-regulated channel in plant cells.

Salt Stress-Induced Cytoplasmic Acidification and Vacuolar Alkalization in Nitellopsis obtusa Cells : In VivoP-Nuclear Magnetic Resonance Study.

Time courses of cytoplasmic and vacuolar pH changes under salt stress were monitored by in vivo(31)P-nuclear magnetic resonance spectroscopy in intact cells of Nitellopsis obtusa. When cells were treated with 100 millimolar NaCl for 2 hours, the cytoplasmic pH deceased from 7.2 to 7.0, while the vacuolar pH increased from 4.9 to 5.2. This salt-induced breakdown of the pH gradient between the cytoplasm and the vacuole was also confirmed through direct measurements of change in vacuolar pH with a micro-pH electrode. We speculate that the intracellular pH changes induced by the salt stress mainly results from the inhibition of the H(+)-translocating pyrophosphatase in the vacuolar membrane, since this H(+)-translocating system is sensitive to salt-induced increase in the cytoplasmic [Na(+)] and a simultaneous decrease in the cytoplasmic [K(+)]. Since disturbance of the cytoplasmic pH value should have serious consequences on the homeostasis of living cells, we propose that the salt-induced intracellular pH changes are one of initial and important steps that lead to cell death.