bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of the shear-mechanical and dielectric relaxation processes in two monoalcohols close to the glass transition
Authors: Jakobsen Bo , Maggi Claudio , Christensen Tage , Dyre Jeppe C.
Published: November 2008

Shear-mechanical and dielectric measurements on the two monohydroxy (monoalcohol) molecular glass formers 2-ethyl-1-hexanol and 2-butanol close to the glass-transition temperature are presented. The shear-mechanical data are obtained using the piezoelectric shear-modulus gauge method covering frequencies from 1 mHz to 10 kHz. The shear-mechanical relaxation spectra show two processes, which follow the typical scenario of a structural (alpha) relaxation and an additional (Johari–Goldstein) beta relaxation. The dielectric relaxation spectra are dominated by a Debye-type peak with an additional non-Debye peak visible. This Debye-type relaxation is a common feature peculiar to monoalcohols. The time scale of the non-Debye dielectric relaxation process is shown to correspond to the mechanical structural (alpha) relaxation. Glass-transition temperatures and fragilities are reported based on the mechanical alpha relaxation and the dielectric Debye-type process, showing that the two glass-transition temperatures differ by approximately 10 K and that the fragility based on the Debye-type process is a factor of 2 smaller than the structural fragility. If a mechanical signature of the Debye-type relaxation exists in these liquids, its relaxation strength is at most 1% and 3% of the full relaxation strength of 2-butanol and 2-ethyl-1-hexanol, respectively. These findings support the notion that it is the non-Debye dielectric relaxation process that corresponds to the structural alpha relaxation in the liquid.
Tunability of the superconductivity of tungsten films grown by focused-ion-beam direct writing
Authors: Li Wuxia , Fenton J. C. , Wang Yiqian , McComb D. W. , Warburton P. A.
Published: November 2008

We have grown tungsten-containing films by focused-ion-beam (FIB)-induced chemical vapor deposition. The films lie close to the metal-insulator transition with an electrical conductivity which changes by less than 5% between room temperature and 7 K. The superconducting transition temperature Tc of the films can be controlled between 5.0 and 6.2 K by varying the ion-beam deposition current. The Tc can be correlated with how far the films are from the metal-insulator transition, showing a nonmonotonic dependence, which is well described by the heuristic model of [Osofsky et al., Phys. Rev. Lett. 87, 197004 (2001)]. Our results suggest that FIB direct-writing of W composites might be a potential approach to fabricate mask-free superconducting devices as well as to explore the role of reduced dimensionality on superconductivity.
GaN-nanowire/amorphous-Si core-shell heterojunction diodes
Authors: Motayed Abhishek , Davydov Albert V.
Published: November 2008

We report the electrical characterization of gallium-nitride/amorphous-silicon (n-type nanowire/p-type shell) diodes fabricated by postgrowth silicon shell formation technique. The n-type (unintentionally doped) gallium-nitride (GaN) nanowires were aligned on prepatterned sapphire substrates using dielectrophoresis. The amorphous silicon (a-Si) shell was deposited using plasma enhanced chemical vapor deposition technique and doped using spin-on boron dopant. Using photolithography, plasma etching, and metal deposition, complete p-n (p-type a-Si shell on n-type GaN nanowire) heterojunction diodes were developed. These diodes had reliable electrical characteristics with 1 V forward turn-on voltage. These nanowire core-shell heterojunction diodes exhibited negative differential resistance, which can be explained by phonon-assisted interband tunneling mechanism.
Reverse graded relaxed buffers for high Ge content SiGe virtual substrates
Authors: Shah V. A. , Dobbie A. , Myronov M. , Fulgoni D. J. F. , Nash L. J. , Leadley D. R.
Published: November 2008

An innovative approach is proposed for epitaxial growth of high Ge content, relaxed Si1−xGex buffer layers on a Si(001) substrate. The advantages of the technique are demonstrated by growing such structures via chemical vapor deposition and their characterization. Relaxed Ge is first grown on the substrate followed by the reverse grading approach to reach a final buffer composition of 0.78. The optimized buffer structure is only 2.8μm thick and demonstrates a low surface threading dislocation density of 4×106cm−2, with a surface roughness of 2.6nm. The buffers demonstrate a relaxation of up to 107%.
Domain switching contribution to piezoelectric response in BaTiO3 single crystals
Authors: Li Fei , Xu Zhuo , Wei Xiaoyong , Yao Xi , Jin Li
Published: November 2008

Piezoelectric responses of barium titanate single crystals are investigated along the [720] and [111] directions, respectively, in order to verify the ultrahigh piezoelectric constant (2000pC∕N) reported in a previous study [Appl. Phys. Lett. 86, 012905 (2005)]. The results suggest that electric-field-induced strain can be largely enhanced by the domain switching in barium titanate single crystal along the [720] direction; however, the piezoelectric response under small field measurement has not been enhanced as much as expected because domain switching is a nonlinear and irreversible process.
Effects of planting season and plant cultivar on growth, development, and pod production in snap bean (Phaseolus vulgaris L.)
Authors: Pérez-Barbeito Marlene , González Ana María , Rodiño Ana Paula , De Ron Antonio Miguel , Santalla Marta
Published: November 2008

The effects of cultivar and planting season on growth development and pod yield of snap bean (Phaseolus vulgaris L.) were analysed in a 2-year, 2-location experiment in Spain. Phenology, pod production, and quality differed significantly among snap bean cultivars. Planting season had a significant effect on most pod traits except the number of seeds per pod, length, thickness, soluble solids content, tenderness, and string, and this effect varied markedly among environments. High and negative correlations for vegetative growth traits between early and late planting seasons confirmed the strong planting season influence on those traits. Fresh pod yields were highest in the early planting season, and the longer pod maturation phase could be considered to be one of the main factors. Planting of snap bean earlier in the season should thus contribute to a longer growing vegetative cycle and greater productivity than normal or summer and late autumn planting. The earliest maturing snap bean cultivars would have the highest fresh pod yields in late planting seasons, while the latest maturing snap bean cultivars would have the highest yields in early and normal planting seasons. These results will allow breeders to optimise the level of earliness for each planting season without reducing the yield. This is a key requirement for snap bean crops, and it is the first step towards selecting parental lines with stability of pod traits to be used in breeding programs for different growing areas and planting seasons.
Further studies on Pea seed-borne mosaic virus in cool-season crop legumes: responses to infection and seed quality defects
Authors: Coutts B. A. , Prince R. T. , Jones R. A. C.
Published: November 2008

Field and glasshouse experiments (3 of each) were done during 2003–06 to determine the responses of a range of genotypes belonging to 13 species of cool-season crop legumes to infection with Pea seed-borne mosaic virus (PSbMV). Seed quality defects were determined and genotypes of some species were also tested for seed transmission of the virus. In field experiments, of 39 genotypes of field pea (Pisum sativum) evaluated, 15 were ranked as highly susceptible, 10 susceptible, 9 moderately resistant, and 5 resistant, while all 7 lupin species (Lupinus spp.) tested were resistant. In glasshouse sap and graft inoculations with PSbMV to genotypes not found infected in the field and 2 additional lupin species, no virus was detected in any of the 9 lupin species or in 5 field pea genotypes tested. Thus, the lupins all appeared to be non-hosts and the 5 field pea genotypes had resistance to the 2 PSbMV isolates used to inoculate them. All 14 genotypes of faba bean (Vicia faba) evaluated in the field were ranked highly susceptible, while 12 out of 16 lentil (Lens culinaris) genotypes were ranked as highly susceptible and 4 as susceptible. Chickpea (Cicer arietinum) genotypes were moderately resistant (50) or susceptible (7). Once infected, plant sensitivities (symptom severities) ranged from low in some field pea and most lentil genotypes to high in most faba bean genotypes. Chickpea genotypes all were ranked as moderately sensitive. Seed lots harvested from PSbMV-infected plants of field pea, faba bean, and chickpea all showed severe seed quality defects, but lentil was usually less affected. The predominant seed symptoms were necrotic rings and line markings on the seed coat, malformation, reduced size, and splitting. Kabuli chickpea types also showed darkening of the seed coat. Seed transmission of PSbMV was detected in faba bean (0.2%) and field pea (5–30%). When PSbMV infection foci were introduced into plots of lentil cv. Nugget, the virus spread to the lentil plants and decreased shoot dry weight by 23%, seed yield by 96%, and individual seed weight by 58%. Seed transmission of PSbMV (6%) was detected in seed from the infected lentil plants. In a survey for possible viral seed symptoms, all seed lots of kabuli chickpea (5) and field pea (70), and 10 of 18 of faba bean were affected, but none of the 23 of lentil. When seedlings from 16 faba bean and 7 field pea seed lots were tested for 3 viruses, neither Broad bean stain virus nor Broad bean true mosaic virus was detected, but PSbMV was found in 5 field pea seed lots at incidences of <1–14%. PSbMV was detected in commercial field pea seed stocks of cvv. Kaspa (33) and Parafield (12) at incidences of 0.5–47% and 0.3–30%, respectively. The implications of these findings in terms of genotype susceptiblility and sensitivity to PSbMV infection and their importance for the management of PSbMV in legume crops are discussed.
Genotypic differences in leaf area maintenance contribute to differences in recovery from water stress in soybean
Authors: Lawn R. J. , Likoswe A. A.
Published: November 2008

Genotypic effects on leaf survival during water deficit stress and subsequent recovery were evaluated using soybean plants grown in tall cylinders in the glasshouse. An initial experiment sought to verify reported genotypic differences in leaf area maintenance under severe water deficit stress. A second experiment sought to test the hypothesis that these putative differences might affect recovery after stress was relieved. Two shoot genotypes, G2120 and cv. Valder, reported to have high and low leaf area retention, respectively, were used in both experiments. In order to preclude the possibility that the reported differences between G2120 and Valder were related to root rather than shoot traits, each shoot was grafted at the cotyledonary stage onto 2 non-self root genotypes, cv. Leichhardt and PI416937. Leichhardt has an apparently normal root, while PI416937 has been reported to be ‘extensively fibrous-rooted’. In the first experiment, water was withheld at the first trifoliolate leaf stage and the plants subjected to terminal water deficit stress. Consistent with the previous report, leaf area was maintained for longer into the stress by the G2120 shoots, with rapid loss of lower leaves not starting until c. 90% of plant-available water (PAW) had been depleted, compared with c. 80% for Valder. The Valder leaves also showed more ‘firing’ damage, with large patches of dead leaf tissue on the retained leaves. Also consistent with the previous report, leaf epidermal conductance to water vapour was lower in G2120 than in Valder. There were no apparent root effects. In the second experiment, water was again withheld at the first trifoliolate leaf stage, and treatments were re-watered when 80%, 85%, 90%, and 95% of the estimated PAW was extracted. Again, G2120 shoots showed better leaf area maintenance during the drying cycle, and less firing damage. When the plants were re-watered, the re-growth of G2120 generally exceeded that of Valder at all levels of PAW depletion. The differences in recovery between G2120 and Valder shoots were sufficient to have agronomic relevance, and confirmed the hypothesis that leaf area retention can affect recovery after severe water deficit stress. Root effects were relatively small. During the drying cycle, leaflet growth was marginally enhanced by Leichhardt relative to PI416937 roots. After re-watering, there was stronger recovery of plants with PI416937 roots, especially those with G2120 shoots. The basis of the differences between the root genotypes is not known but the stronger recovery of PI416937 may reflect its putative ‘extensively fibrous’ nature.
Virtual phyllotaxis and real plant model cases
Authors: Zagórska-Marek Beata , Szpak Marcin
Published: November 2008

Phyllotactic pattern results from genetic control of lateral primordia size (physiological or physical) relative to the size of organogenic lateral surface of shoot apical meristem (SAM). In order to understand the diversity of patterns and ontogenetic transitions of phyllotaxis we have developed a geometric model allowing changes of the above proportion in a computer simulation of SAM’s growth. The results of serial simulations confirmed that many phyllotactic patterns (including most esoteric ones) and ontogenetic transitions known from real plant model cases can be easily obtained in silico. Properties of virtual patterns often deviated from those of ideal mathematical lattices but closely resembled those of the natural ones. This proved the assumptions of the model, such as initiation in the first available space or ontogenetic changes in primordia size, to be quite realistic. Confrontation of simulation results with some sequences of real phyllotactic patterns (case study Verbena) questions the autonomy of SAM in its organogenic activity and suggests the involvement of unknown signal positioning primordia in a non-random manner in the first available space.
Hosts of Phakopsora pachyrhizi Identified in Field Evaluations in Florida
Authors: Slaminko T. L. , Miles M. R. , Marois J. J. , Wright D. L. , Hartman G. L.
Published: November 2008

Phakopsora pachyrhizi, the causal organism of soybean rust, was first found on Glycine max in the continental United States in 2004, and subsequently on Pueraria lobata, Desmodium tortuosum, three Phaseolus species, and Erythrina herbacea in the field. The pathogen has been reported to occur on over 150 legume species worldwide, and it is likely to infect native and introduced legume species in the USA. The objective of this study was to determine if USA-native or -naturalized legume species could become infected with P. pachyrhizi in field conditions. A total of 80 accessions representing 52 species in 29 genera were infected in the field trials. Crotalaria retusa, Lathyrus latifolius, Phaseolus angustissimus, P. polystachios, and Robinia hispida are new hosts. This is the first report showing the broad host range of P. pachyrhizi based on field infections in the USA. Some of these hosts grow in the southern USA, and could, like kudzu, overwinter P. pachyrhizi.

Accepted for publication 18 August 2008. Published 3 November 2008.
Effect of Soybean Cyst Nematode on Fatty Acid Levels of Soybean Seed
Authors: Beuselinck P. R.
Published: November 2008

Growing soybean cyst nematode (SCN, Heterodera glycines Ichinohe) resistant varieties in fields infested with SCN can improve yield, but the impact of SCN on seed quality of lines with modified seed composition is unknown. The objective of this study was to determine if SCN resistant or susceptible rootstock influenced the composition of seed of soybean lines developed for desirable elevated levels of unsaturated fatty acids (FA). Five soybean lines with modified or normal levels of FA were Y-grafted to generate a 5-×-5 combination of plants with a SCN susceptible (SCNS) or resistant (SCNR) rootstock having a self-grafted branch, a scion (alien) grafted branch, or non-grafted branch; control plants were not grafted. In 2004 and 2005 plants were transplanted into blocks of Asgrow 3302 (SCNR) or Asgrow 3701 (SCNS) verified to be infested with SCN. Seeds were harvested at physiologic maturity (R8) in 2004 and 2005 and analyzed for five unsaturated FA. Differences in FA levels between 2004 and 2005 were significant (P < 0.05), but there were no significant (P = 0.05) block × year effects. Significant differences were observed between the FA levels of seed harvested from non-grafted control plants and self-grafted or non-grafted branches of grafted plants within lines. Seed oleic acid of the mid-oleic line S03-1379-2 was significantly greater when grafted onto an SCNR line than when grafted onto SCNS lines. The low linolenate trait appeared to be insensitive to SCN presence as seed linolenic acid of the low linolenic line IA-3017 was not different when grafted onto SCNR or SCNS lines. SCN can negatively impact the expression of seed quality of soybean if grown where SCN infestations are evident.

Accepted for publication 8 September 2008. Published 3 November 2008.
Assimilatory Sulfate Reduction in C3, C3-C4, and C4 Species ofFlaveria
Authors: Koprivova Anna , Melzer Michael , von Ballmoos Peter , Mandel Therese , Brunold Christian , Kopriva Stanislav
Published: November 2008

The activity of the enzymes catalyzing the first two steps of sulfate assimilation, ATP sulfurylase and adenosine 5′-phosphosulfate reductase (APR), are confined to bundle sheath cells in several C4 monocot species. With the aim to analyze the molecular basis of this distribution and to determine whether it was a prerequisite or a consequence of the C4 photosynthetic mechanism, we compared the intercellular distribution of the activity and the mRNA of APR in C3, C3-C4, C4-like, and C4 species of the dicot genusFlaveria. Measurements of APR activity, mRNA level, and protein accumulation in six Flaveria species revealed that APR activity, cysteine, and glutathione levels were significantly higher in C4-like and C4 species than in C3 and C3-C4 species. ATP sulfurylase and APR mRNA were present at comparable levels in both mesophyll and bundle sheath cells of C4 speciesFlaveria trinervia. Immunogold electron microscopy demonstrated the presence of APR protein in chloroplasts of both cell types. These findings, taken together with results from the literature, show that the localization of assimilatory sulfate reduction in the bundle sheath cells is not ubiquitous among C4 plants and therefore is neither a prerequisite nor a consequence of C4photosynthesis.
Developmental and Thermal Regulation of the Maize Heat Shock Protein, HSP101
Authors: Young Todd E. , Ling Jun , Geisler-Lee C. Jane , Tanguay Robert L. , Caldwell Christian , Gallie Daniel R.
Published: November 2008

The plant heat stress protein, Hsp101, and the yeast ortholog, Hsp104, are required to confer thermotolerance in plants and yeast (Saccharomyces cerevisiae), respectively. In addition to its function during stress, Hsp101 is developmentally regulated in plants although its function during development is not known. To determine how the expression of Hsp101 is regulated in cereals, we investigated the Hsp101 expression profile in developing maize (Zea mays). Hsp101 protein was most abundant in the developing tassel, ear, silks, endosperm, and embryo. It was less abundant in the vegetative and floral meristematic regions and was present at only a low level in the anthers and tassel at anthesis, mature pollen, roots, and leaves. As expected, heat treatment resulted in an increase in the level of Hsp101 protein in several organs. In expanding foliar leaves, husk leaves, the tassel at the premeiosis stage of development, or pre-anthesis anthers, however, the heat-mediated increase in protein was not accompanied by an equivalent increase in mRNA. In contrast, the level of Hsp101 transcript increased in the tassel at anthesis following a heat stress without an increase in Hsp101 protein. In other organs such as the vegetative and floral meristematic regions, fully expanded foliar leaves, the young ear, and roots, the heat-induced increase in Hsp101 protein was accompanied by a corresponding increase in Hsp101 transcript level. However, anthers at anthesis, mature pollen, developing endosperm, and embryos largely failed to mount a heat stress response at the level of Hsp101 protein or mRNA, indicating that Hsp101 expression is not heat inducible in these organs. In situ RNA localization analysis revealed that Hsp101 mRNA accumulated in the subaleurone and aleurone of developing kernels and was highest in the root cap meristem and quiescent center of heat-stressed roots. These data suggest an organ-specific control of Hsp101 expression during development and following a heat stress through mechanisms that may include posttranscriptional regulation.
Xylem Water Content and Wood Density in Spruce and Oak Trees Detected by High-Resolution Computed Tomography
Authors: Fromm Jörg H. , Sautter Irina , Matthies Dietmar , Kremer Johannes , Schumacher Peter , Ganter Carl
Published: November 2008

Elucidation of the mechanisms involved in long-distance water transport in trees requires knowledge of the water distribution within the sapwood and heartwood of the stem as well as of the earlywood and latewood of an annual ring. X-ray computed tomography is a powerful tool for measuring density distributions and water contents in the xylem with high spatial resolution. Ten- to 20-year-old spruce (Picea abies L. KARST.) and oak (Quercus robur) trees grown in the field were used throughout the experiments. Stem and branch discs were collected from different tree heights, immediately deep frozen, and used for the tomographic determinations of spatial water distributions. Results are presented for single-tree individuals, demonstrating heartwood and sapwood distribution throughout their entire length as well as the water relations in single annual rings of both types of wood. Tree rings of the sapwood show steep water gradients from latewood to earlywood, whereas those of the heartwood reflect water deficiency in both species. Although only the latest two annual rings of the ringporous species are generally assumed to transport water, we found similar amounts of water and no tyloses in all rings of the oak sapwood, which indicates that at least water storage is important in the whole sapwood.
Conditional Circadian Regulation of PHYTOCHROME AGene Expression
Authors: Hall Anthony , Kozma-Bognár László , Tóth Réka , Nagy Ferenc , Millar Andrew J.
Published: November 2008

The phytochrome photoreceptors and the circadian clock control many of the same developmental processes, in all organs and throughout the growth of Arabidopsis plants. Phytochrome A (phyA) provides light input signals to entrain the circadian clock. The clock is known to rhythmically regulate its light input pathway, so we tested rhythmic regulation of phyA, using transgenic plants carrying aPHYA promoter fusion to the luciferase reporter (PHYA:LUC). We provide the first images ofLUC activity with subcellular resolution in intact tissue. PHYA transcription and the accumulation of all three PHYA mRNAs were indeed clock controlled.PHYA is expressed throughout the seedling, so we tested whether circadian rhythms were observed in allPHYA-expressing organs and whether the rhythms were autonomously controlled by each organ. In contrast to our previous results using other clock controlled genes, the rhythmic pattern ofPHYA expression varied markedly among isolated organs and between isolated organs and intact plants. High-amplitude rhythms were maintained for many days in isolated leaves in darkness, whereas the leaves of intact plants rapidly lost rhythmicity. Wounding the leaves of intact plants had no effect. The rhythmic pattern ofPHYA expression is not organ autonomous but depends upon the physical continuity or isolation of the rhythmic tissues, consistent with the presence of a transmitted signal that controls the overt expression of circadian rhythms without necessarily affecting the underlying clock. A circadian system might be present in most, if not all, plant cells, but its effect on intracellular rhythms can be controlled by supracellular signaling.
The Maize CRINKLY4 Receptor Kinase Controls a Cell-Autonomous Differentiation Response
Authors: Becraft Philip W. , Kang Suk-Hoon , Suh Sang-Gon
Published: November 2008

The maize (Zea mays)CRINKLY4 (cr4) gene encodes a receptor-like kinase that controls a variety of cell differentiation responses, particularly in the leaf epidermis and in the aleurone of the endosperm. In situ hybridization indicated that the cr4 transcript is present throughout the shoot apical meristem and young leaf primordia. A genetic mosaic analysis was conducted to test whether CR4 signal transduction directly regulated the cellular processes associated with differentiation or whether differentiation was controlled through the production of a secondary signal. Genetic mosaics were created using γ-rays to induce chromosome breakage in a cr4/Cr4+ heterozygote. The mutant cr4 allele was marked with the albino mutation,Oy-700. Breakage and loss of the chromosome arm carrying the wild-type alleles created a sector of albino, cr4mutant tissue in an otherwise normal leaf. Analysis of such sectors indicated that cr4 functions cell autonomously to regulate cell morphogenesis, implying that CR4 signal transduction regulates cell differentiation through strictly intracellular functions and not the production of secondary intercellular signals. However, several sectors altered cell patterning in wild-type tissue adjacent to the sectors, suggesting that cr4 mutant cells are defective in the production of other lateral signals.
The ArabidopsisSomatic Embryogenesis Receptor Kinase 1Gene Is Expressed in Developing Ovules and Embryos and Enhances Embryogenic Competence in Culture
Authors: Hecht Valérie , Vielle-Calzada Jean-Philippe , Hartog Marijke V. , Schmidt Ed D.L. , Boutilier Kim , Grossniklaus Ueli , de Vries Sacco C.
Published: November 2008

We report here the isolation of the Arabidopsis SOMATIC EMBRYOGENESIS RECEPTOR-LIKE KINASE 1 (AtSERK1) gene and we demonstrate its role during establishment of somatic embryogenesis in culture. The AtSERK1 gene is highly expressed during embryogenic cell formation in culture and during early embryogenesis. The AtSERK1 gene is first expressed in planta during megasporogenesis in the nucleus of developing ovules, in the functional megaspore, and in all cells of the embryo sac up to fertilization. After fertilization, AtSERK1 expression is seen in all cells of the developing embryo until the heart stage. After this stage, AtSERK1 expression is no longer detectable in the embryo or in any part of the developing seed. Low expression is detected in adult vascular tissue. Ectopic expression of the full-length AtSERK1 cDNA under the control of the cauliflower mosaic virus 35S promoter did not result in any altered plant phenotype. However, seedlings that overexpressed theAtSERK1 mRNA exhibited a 3- to 4-fold increase in efficiency for initiation of somatic embryogenesis. Thus, an increased AtSERK1 level is sufficient to confer embryogenic competence in culture.
Biochemical Characterization of the Arabidopsis Biotin Synthase Reaction. The Importance of Mitochondria in Biotin Synthesis
Authors: Picciocchi Antoine , Douce Roland , Alban Claude
Published: November 2008

Biotin synthase, encoded by the bio2 gene in Arabidopsis, catalyzes the final step in the biotin biosynthetic pathway. The development of radiochemical and biological detection methods allowed the first detection and accurate quantification of a plant biotin synthase activity, using protein extracts from bacteria overexpressing the Arabidopsis Bio2 protein. Under optimized conditions, the turnover number of the reaction was >2 h−1 with this in vitro system. Purified Bio2 protein was not efficient by itself in supporting biotin synthesis. However, heterologous interactions between the plant Bio2 protein and bacterial accessory proteins yielded a functional biotin synthase complex. Biotin synthase in this heterologous system obeyed Michaelis-Menten kinetics with respect to dethiobiotin (K  m = 30 μm) and exhibited a kinetic cooperativity with respect toS-adenosyl-methionine (Hill coefficient = 1.9;K  0.5 = 39 μm), an obligatory cofactor of the reaction. In vitro inhibition of biotin synthase activity by acidomycin, a structural analog of biotin, showed that biotin synthase reaction was the specific target of this inhibitor of biotin synthesis. It is important that combination experiments using purified Bio2 protein and extracts from pea (Pisum sativum) leaf or potato (Solanum tuberosum) organelles showed that only mitochondrial fractions could elicit biotin formation in the plant-reconstituted system. Our data demonstrated that one or more unidentified factors from mitochondrial matrix (pea and potato) and from mitochondrial membranes (pea), in addition to the Bio2 protein, are obligatory for the conversion of dethiobiotin to biotin, highlighting the importance of mitochondria in plant biotin synthesis.
Effects of Natural Intensities of Visible and Ultraviolet Radiation on Epidermal Ultraviolet Screening and Photosynthesis in Grape Leaves
Authors: Kolb Christiane A. , Käser Martin A. , Kopecký Jiri , Zotz Gerhard , Riederer Markus , Pfündel Erhard E.
Published: November 2008

Grape (Vitis vinifera cv Silvaner) vine plants were cultivated under shaded conditions in the absence of ultraviolet (UV) radiation in a greenhouse, and subsequently placed outdoors under three different light regimes for 7 d. Different light regimes were produced by filters transmitting natural radiation, or screening out the UV-B (280–315 nm), or screening out the UV-A (315–400 nm) and the UV-B spectral range. During exposure, synthesis of UV-screening phenolics in leaves was quantified using HPLC: All treatments increased concentrations of hydroxycinnamic acids but the rise was highest, reaching 230% of the initial value, when UV radiation was absent. In contrast, UV-B radiation specifically increased flavonoid concentrations resulting in more than a 10-fold increase. Transmittance in the UV of all extracted phenolics was lower than epidermal UV transmittance determined fluorimetrically, and the two parameters were curvilinearly related. It is suggested that curvilinearity results from different absorption properties of the homogeneously dissolved phenolics in extracts and of the non-homogeneous distribution of phenolics in the epidermis. UV-B-dependent inhibition of maximum photochemical yield of photosystem II (PSII), measured as variable fluorescence of dark-adapted leaves, recovered in parallel to the buildup of epidermal screening for UV-B radiation, suggesting that PSII is protected against UV-B damage by epidermal screening. However, UV-B inhibition of CO2assimilation rates was not diminished by efficient UV-B screening. We propose that protection of UV-B inactivation of PSII is observed because preceding damage is efficiently repaired while those factors determining UV-B inhibition of CO2 assimilation recover more slowly.
Isolation and Characterization of Mutants Defective in Seed Coat Mucilage Secretory Cell Development in Arabidopsis
Authors: Western Tamara L. , Burn Joanne , Tan Wei Ling , Skinner Debra J. , Martin-McCaffrey Luke , Moffatt Barbara A. , Haughn George W.
Published: November 2008

In Arabidopsis, fertilization induces the epidermal cells of the outer ovule integument to differentiate into a specialized seed coat cell type producing extracellular pectinaceous mucilage and a volcano-shaped secondary cell wall. Differentiation involves a regulated series of cytological events including growth, cytoplasmic rearrangement, mucilage synthesis, and secondary cell wall production. We have tested the potential of Arabidopsis seed coat epidermal cells as a model system for the genetic analysis of these processes. A screen for mutants defective in seed mucilage identified five novel genes (MUCILAGE-MODIFIED [MUM]1–5). The seed coat development of these mutants, and that of three previously identified ones (TRANSPARENT TESTA GLABRA1, GLABRA2, and APETALA2) were characterized. Our results show that the genes identified define several events in seed coat differentiation. Although APETALA2is needed for differentiation of both outer layers of the seed coat,TRANSPARENT TESTA GLABRA1, GLABRA2, andMUM4 are required for complete mucilage synthesis and cytoplasmic rearrangement. MUM3 and MUM5may be involved in the regulation of mucilage composition, whereasMUM1 and MUM2 appear to play novel roles in post-synthesis cell wall modifications necessary for mucilage extrusion.
Rapid Isolation of Monoclonal Antibodies. Monitoring Enzymes in the Phytochelatin Synthesis Pathway
Authors: Li Yujing , Kandasamy Muthugapatti K. , Meagher Richard B.
Published: November 2008

Genomics projects have identified thousands of interesting new genes whose protein products need to be examined at the tissue, subcellular, and molecular levels. Furthermore, modern metabolic engineering requires accurate control of expression levels of multiple enzymes in complex pathways. The lack of specific immune reagents for characterization and monitoring of these numerous proteins limits all proteomic and metabolic engineering projects. We describe a rapid method of isolating monoclonal antibodies that required only sequence information from GenBank. We show that large synthetic peptides were highly immunogenic in mice and crude protein extracts were effective sources of antigen, thus eliminating the time-consuming step of purifying the target proteins for antibody production. A case study was made of the three-enzyme pathway for the synthesis of phytochelatins. Enzyme-linked immunosorbent assays and western blots with the recombinant proteins in crude extracts demonstrated that the monoclonal antibodies produced to synthetic peptides were highly specific for the different target proteins, gamma-glutamyl cysteine synthetase, glutathione synthetase, and phytochelatin synthase. Moreover, immunofluorescence localization studies with antibacterial γ-glutamyl cysteine synthetase and antiglutathione synthetase antibodies demonstrated that these immune reagents reacted strongly with their respective target proteins in chemically fixed cells from transgenic plants. This approach enables research to progress rapidly from the genomic sequence of poorly characterized target genes, to protein-specific antibodies, to functional studies.
Effects of Phosphorylation on Phosphoenolpyruvate Carboxykinase from the C4 Plant Guinea Grass
Authors: Walker Robert P. , Chen Zhi-Hui , Acheson Richard M. , Leegood Richard C.
Published: November 2008

In the C4 plant Guinea grass (Panicum maximum), phosphoenolpyruvate carboxykinase (PEPCK) is phosphorylated in darkened leaves and dephosphorylated in illuminated leaves. To determine whether the properties of phosphorylated and non-phosphorylated PEPCK were different, PEPCK was purified to homogeneity from both illuminated and darkened leaves. The final step of the purification procedure, gel filtration chromatography, further separated phosphorylated and non-phosphorylated forms. In the presence of a high ratio of ATP to ADP, the non-phosphorylated enzyme had a higher affinity for its substrates, oxaloacetate and phosphoenolpyruvate. The activity of the non-phosphorylated form was up to 6-fold higher when measured at low substrate concentrations. Comparison of proteoloytically cleaved PEPCK from Guinea grass, which lacked its N-terminal extension, from yeast (Saccharomyces cerevisiae), which does not possess an N-terminal extension, and from the C4 plantUrochloa panicoides, which possesses an N-terminal extension but is not subject to phosphorylation, revealed similar properties to the non-phosphorylated full-length form from Guinea grass. Assay of PEPCK activity in crude extracts of Guinea grass leaves, showed a large difference between illuminated and darkened leaves when measured in a selective assay (a low concentration of phosphoenolpyruvate and a high ratio of ATP to ADP), but there was no difference under assay conditions used to estimate maximum activity. Immunoblots of sodium dodecyl sulfate-polyacrylamide gel electrophoresis gels showed no difference in the abundance of PEPCK protein in illuminated and darkened leaves. There were no light/dark differences in activity detected in maize (Zea mays) leaves, in which PEPCK is not subject to phosphorylation.
Arabidopsis Dynamin-Like 2 That Binds Specifically to Phosphatidylinositol 4-Phosphate Assembles into a High-Molecular Weight Complex in Vivo and in Vitro
Authors: Kim Yong-Woo , Park Dae-Sup , Park Seung-Cheol , Kim Sung Hee , Cheong Gang-Won , Hwang Inhwan
Published: November 2008

Arabadopsis dynamin-like (ADL) 2, a member of the high-molecular weight (M  r) dynamin family found in Arabidopsis, has been shown to be targeted to the plastid. In the chloroplast, most of the ADL2 was present in the fraction containing the envelope membranes when analyzed by suborganellar fractionation. Sucrose gradient and gel filtration experiments showed that when associated with membranes, ADL2 existed as a high-M  r complex, whereas the soluble form existed as a monomer. The recombinant ADL2 expressed inEscherichia coli was present as a high-M  r form and showed higher GTPase activity at a low NaCl concentration, whereas ADL2 existed as a low-M  r form with a low level of GTPase activity at a high NaCl concentration. Electron microscopy studies revealed that the purified recombinant ADL2 formed spiral-coiled structures or rings. In the presence of guanosine-5′-O-(3-thio)triphosphate, these structures were transformed into a long rod structure. In contrast, in the presence of GDP, these structures disassembled into oligomers that were shown to be tetramer with 4-fold symmetry. Finally, a lipid-binding assay revealed that recombinant ADL2 purified fromE. coli bound specifically to phosphatidylinositol 4-phosphate. Together, these results demonstrated that the biochemical properties of ADL2 were very similar to those of dynamin and other related proteins. Based on this similarity, we propose that ADL2 may be involved in vesicle formation at the chloroplast envelope membrane.
Translocation and Utilization of Fungal Storage Lipid in the Arbuscular Mycorrhizal Symbiosis
Authors: Bago Berta , Zipfel Warren , Williams Rebecca M. , Jun Jeongwon , Arreola Raoul , Lammers Peter J. , Pfeffer Philip E. , Shachar-Hill Yair
Published: November 2008

The arbuscular mycorrhizal (AM) symbiosis is responsible for huge fluxes of photosynthetically fixed carbon from plants to the soil. Carbon is transferred from the plant to the fungus as hexose, but the main form of carbon stored by the mycobiont at all stages of its life cycle is triacylglycerol. Previous isotopic labeling experiments showed that the fungus exports this storage lipid from the intraradical mycelium (IRM) to the extraradical mycelium (ERM). Here, in vivo multiphoton microscopy was used to observe the movement of lipid bodies through the fungal colony and to determine their sizes, distribution, and velocities. The distribution of lipid bodies along fungal hyphae suggests that they are progressively consumed as they move toward growing tips. We report the isolation and measurements of expression of an AM fungal expressed sequence tag that encodes a putative acyl-coenzyme A dehydrogenase; its deduced amino acid sequence suggests that it may function in the anabolic flux of carbon from lipid to carbohydrate. Time-lapse image sequences show lipid bodies moving in both directions along hyphae and nuclear magnetic resonance analysis of labeling patterns after supplying 13C-labeled glycerol to either extraradical hyphae or colonized roots shows that there is indeed significant bidirectional translocation between IRM and ERM. We conclude that large amounts of lipid are translocated within the AM fungal colony and that, whereas net movement is from the IRM to the ERM, there is also substantial recirculation throughout the fungus.
Circadian Clock-Regulated Expression of Phytochrome and Cryptochrome Genes in Arabidopsis
Authors: Tóth Réka , Kevei Éva , Hall Anthony , Millar Andrew J. , Nagy Ferenc , Kozma-Bognár László
Published: November 2008

Many physiological and biochemical processes in plants exhibit endogenous rhythms with a period of about 24 h. Endogenous oscillators called circadian clocks regulate these rhythms. The circadian clocks are synchronized to the periodic environmental changes (e.g. day/night cycles) by specific stimuli; among these, the most important is the light. Photoreceptors, phytochromes, and cryptochromes are involved in setting the clock by transducing the light signal to the central oscillator. In this work, we analyzed the spatial, temporal, and long-term light-regulated expression patterns of the Arabidopsis phytochrome (PHYA toPHYE) and cryptochrome (CRY1 andCRY2) promoters fused to the luciferase (LUC  +) reporter gene. The results revealed new details of the tissue-specific expression and light regulation of the PHYC and CRY1 and2 promoters. More importantly, the data obtained demonstrate that the activities of the promoter::LUC  + constructs, with the exception ofPHYC::LUC  +, display circadian oscillations under constant conditions. In addition, it is shown by measuring the mRNA abundance of PHY andCRY genes under constant light conditions that the circadian control is also maintained at the level of mRNA accumulation. These observations indicate that the plant circadian clock controls the expression of these photoreceptors, revealing the formation of a new regulatory loop that could modulate gating and resetting of the circadian clock.
Isoprene Produced by Leaves Protects the Photosynthetic Apparatus against Ozone Damage, Quenches Ozone Products, and Reduces Lipid Peroxidation of Cellular Membranes
Authors: Loreto Francesco , Velikova Violeta
Published: November 2008

Many plants invest carbon to form isoprene. The role of isoprene in plants is unclear, but many experiments showed that isoprene may have a role in protecting plants from thermal damage. A more general antioxidant action has been recently hypothesized on the basis of the protection offered by exogenous isoprene in nonemitting plants exposed to acute ozone doses. We inhibited the synthesis of endogenous isoprene by feeding fosmidomycin and observed that Phragmites australis leaves became more sensitive to ozone than those leaves forming isoprene. Photosynthesis, stomatal conductance, and fluorescence parameters were significantly affected by ozone only in leaves on which isoprene was not formed. The protective effect of isoprene was more evident when the leaves were exposed for a long time (8 h) to relatively low (100 nL L−1) ozone levels than when the exposure was short and acute (3 h at 300 nL L−1). Isoprene quenched the amount of H2O2 formed in leaves and reduced lipid peroxidation of cellular membranes caused by ozone. These results indicate that isoprene may exert its protective action at the membrane level, although a similar effect could be obtained if isoprene reacted with ozone before forming active oxygen species. Irrespective of the mechanism, our results suggest that endogenous isoprene has an important antioxidant role in plants.
A Physical Amplified Fragment-Length Polymorphism Map of Arabidopsis
Authors: Peters Janny L. , Constandt Hans , Neyt Pia , Cnops Gerda , Zethof Jan , Zabeau Marc , Gerats Tom
Published: November 2008

We have positioned amplified fragment-length polymorphism (AFLP) markers directly on the genome sequence of a complex organism, Arabidopsis, by combining gel-based AFLP analysis with in silico restriction fragment analysis using the published genome sequence. For placement of the markers, we used information on restriction fragment size, four selective nucleotides, and the rough genetic position of the markers as deduced from the analysis of a limited number of Columbia (Col)/Landsberg (Ler) recombinant inbred lines. This approach allows for exact physical positioning of markers as opposed to the statistical localization resulting from traditional genetic mapping procedures. In addition, it is fast because no extensive segregation analysis is needed. In principle, the method can be applied to all organisms for which a complete or nearly complete genome sequence is available. We have located 1,267 AFLP Col/Ler markers resulting from 256SacI+2, MseI+2 primer combinations to a physical position on the Arabidopsis genome. The positioning was verified by sequence analysis of 70 markers and by segregation analysis of two leaf-form mutants. Approximately 50% of the mapped Col/Ler AFLP markers can be used for segregation analysis in Col/C24, Col/Wassilewskija, or Col/Cape Verde Islands crosses. We present data on one such cross: the localization of a viviparous-like mutant segregating in a Col/C24 cross.
The Arabidopsis Xylem Peptidase XCP1 Is a Tracheary Element Vacuolar Protein That May Be a Papain Ortholog
Authors: Funk Vanessa , Kositsup Boonthida , Zhao Chengsong , Beers Eric P.
Published: November 2008

XCP1 is a xylem-specific papain-like cysteine peptidase in Arabidopsis. To determine whether XCP1 could be involved in tracheary element autolysis, promoter activity and localization of XCP1 were investigated using XCP1 promoter-β-glucuronidase fusions and immunofluorescence confocal microscopy. A tracheary element expression pattern was detected for XCP1. Results from confocal microscopy and biochemical subcellular fractionation indicated that XCP1 was localized in the vacuole. Ectopic expression ofXCP1 resulted in a reduction in plant size in some lines and early leaf senescence, as indicated by early loss of leaf chlorophyll. Reduced plant size was correlated with higher levels of XCP1, as shown by immunoblot and peptidase activity gel analyses. The XCP1 prodomain exhibits exceptionally high similarity (greater than 80%) to the prodomains of papain and other papain-like enzymes isolated from papaya (Carica papaya) laticifers when compared with all other reported papain-like enzymes. The potential for XCP1 and papain to perform common functions as catalysts of autolytic processing following cell death due to programmed suicide or to wounding is discussed.
A Grapevine Gene Encoding a Guard Cell K+ Channel Displays Developmental Regulation in the Grapevine Berry
Authors: Pratelli Réjane , Lacombe Benoı̂t , Torregrosa Laurent , Gaymard Frédéric , Romieu Charles , Thibaud Jean-Baptiste , Sentenac Hervé
Published: November 2008

SIRK is a K+ channel identified in grapevine (Vitis vinifera), belonging to the so-called Shaker family. The highest sequence similarities it shares with the members of this family are found with channels of the KAT type, although SIRK displays a small ankyrin domain. This atypical feature provides a key to understand the evolution of the plant Shaker family. Expression inXenopus laevis oocytes indicated that SIRK is an inwardly rectifying channel displaying functional properties very similar to those of KAT2. The activity of SIRK promoter region fused to the GUS reporter gene was analyzed in both grapevine and Arabidopsis. Like other KAT-like channels,SIRK is expressed in guard cells. In Arabidopsis, the construct is also expressed in xylem parenchyma. Semiquantitative reverse transcriptase-polymerase chain reaction experiments indicated that SIRK transcript was present at low levels in the berry, during the first stages of berry growth. After veraison, the period of berry development that corresponds to the inception of ripening and that is associated with large biochemical and structural modifications, such as evolution of stomata in nonfunctional lenticels and degeneration of xylem vasculature, the transcript was no longer detected. The whole set of data suggests that in the berriesSIRK is expressed in guard cells and, possibly, in xylem tissues. The encoded channel polypeptide could therefore play a role in the regulation of transpiration and water fluxes in grapevine fruits.