bluuebunny/crossref_metadata_2025 huggingface dataset:
The effect of an additional infrared laser on the carrier collection efficiency of InAs quantum dots
Authors: Moskalenko E. S. , Karlsson K. F. , Donchev V. , Holtz P. O. , Schoenfeld W. V. , Petroff P. M.
Published: June 2004

We report a micro-photoluminescence study on the influence of single and multi-quantum dots (QDs) on the exposure by a low-energy laser, in addition to the principal exciting laser. At low temperatures, the presence of the low-energy laser effectively quenches the single QD luminescence. This can be explained in terms of an induced screening of a built-in electric field, which plays an important role as a carrier capture mechanism. The influence of the low-energy laser is successively decreasing when the capture efficiency is increased either by elevated crystal temperature or by increased QD densities, full consistent with the proposed model.
A low switching voltage organic-on-inorganic heterojunction memory element utilizing a conductive polymer fuse on a doped silicon substrate
Authors: Smith Shawn , Forrest Stephen R.
Published: June 2004

We present a simple, nonvolatile, write-once-read-many-times (WORM) memory device utilizing an organic-on-inorganic heterojunction (OI–HJ) diode with a conductive polymer fuse consisting of polyethylene dioxythiophene:polysterene sulfonic acid (PEDOT:PSS) forming one side of the rectifying junction. Current transients are used to change the fuse from a conducting to a nonconducting state to record a logical “1” or “0”, while the nonlinearity of the OI–HJ allows for passive matrix memory addressing. The device switches at 2 and 4 V for 50 nm thick PEDOT:PSS films on p-type Si and n-type Si, respectively. This is significantly lower than the switching voltage used in PEDOT:PSS/p-i-n Si memory elements [J. Appl Phys. 94, 7811 (2003)]. The switching results in a permanent reduction of forward-bias current by approximately five orders of magnitude. These results suggest that the OI–HJ structure has potential for use in low-cost passive matrix WORM memories for archival storage applications.
Photoresponse of sol-gel-synthesized ZnO nanorods
Authors: Ahn Seung Eon , Lee Jong Soo , Kim Hyunsuk , Kim Sangsig , Kang Byung Hyun , Kim Kang Hyun , Kim Gyu Tae
Published: June 2004

ZnO nanorods were grown on SiO2/Si substrates by a sol-gel method at low temperatures of around T=95 °C. The diameters and the lengths of ZnO nanorods increased at high concentrations of zinc nitrate hexahydrate and methenamine solution. Current–voltage characteristics of the ZnO nanorods network followed a typical nonlinear behavior with significant photoresponse below λ<400 nm in air, and the conductance was enhanced in vacuum with negligible photoresponse. In photoluminescence (PL) and photocurrent (PC) spectra, the PL peak (λpeak=380 nm and 3.26 eV) did not match the PC edge (λedge=400 nm and 3.1 eV), indicating the nondirect band-gap transition in photocurrent. The origin of the photocurrent was discussed from the point of the influence of the desorption of adsorbed water molecules on the surface or inside the ZnO nanorods.
Maskless lateral epitaxial overgrowth of high-aluminum-content AlxGa1−xN
Authors: Katona T. M. , Cantu P. , Keller S. , Wu Y. , Speck J. S. , DenBaars S. P.
Published: June 2004

We have demonstrated maskless lateral epitaxial overgrowth of Al0.96Ga0.04N on sapphire for dislocation reduction. 600 nm and 1 μm thick AlN layers were grown on sapphire via metalorganic chemical vapor deposition. Parallel, periodic trenches were then etched in the AlN and Al0.96Ga0.04N was regrown laterally from the unetched mesas. Significant threading dislocation reduction was observed for “wing” material, growing laterally, compared to “seed” material, growing vertically from the unetched mesa, as observed by atomic force microscopy, and transmission electron microscopy. Crystallographic wing tilt of ∼0.23° was measured by x-ray diffraction.
Atomic-scale structural evolution of Ge(100) surfaces etched by H and D
Authors: Lee Jun Young , Jung Soon Jung , Maeng Jae Yeol , Cho Young Eun , Kim Sehun , Jo Sam K.
Published: June 2004

The atomic-scale structural evolution of Ge(100) surfaces etched by H(g) and D(g) at Ts=400 K is studied using scanning tunneling microcopy (STM) and field emission-scanning electron microscopy (FE-SEM). The STM investigation reveals that etching of the Ge(100) by H(g) and D(g) proceeds initially via the production of single atom vacancies (SV), dimer vacancies (DV), and subsequently, line defects along the Ge dimer rows. It is also observed that D(g) etches the Ge(100) surface eight times faster than H(g) does. After extensive exposures of the surface to H(g), the FE-SEM images show square etch pits with V-groove shapes, indicating that H(g) etching of the Ge(100) surface proceeds anisotropically.
Interfacial interactions at Au/Si3N4/Si(111) and Ni/Si3N4/Si(111) structures with ultrathin nitride films
Authors: Aballe L. , Gregoratti L. , Barinov A. , Kiskinova M. , Clausen T. , Gangopadhyay S. , Falta J.
Published: June 2004

Synchrotron photoemission spectromicroscopy has been used to study the interfacial interactions, metal diffusivity, and electronic barriers of Au and Ni contacts on ultrathin silicon nitride films. The Au/Si3N4 interface was found to be nonreactive, and only in the case of a very thin nitride film and elevated temperatures, Si can segregate from the Si(111) substrate and interact with Au. In the case of Ni/Si3N4/Si(111) structures, Ni diffusion and degradation of the Si3N4 lattice are evidenced even at room temperature and strongly enhanced at elevated temperatures, leading to formation of a Ni silicide interlayer.
Stress field in sputtered thin films: Ion irradiation as a tool to induce relaxation and investigate the origin of growth stress
Authors: Debelle A. , Abadias G. , Michel A. , Jaouen C.
Published: June 2004

The stress state of sputtered Mo thin films was studied, and a detailed analysis of elastic strains, using x-ray diffraction and the “sin2 Ψ method,” was performed. The evolution of the lattice parameter under ion irradiation showed that the usual assumption of a biaxial stress state is not adequate to determine the true stress-free lattice parameter a0 of the film. An original stress model, including a hydrostatic component linked to volume distortions induced by point defects, is required. This model, which describes a triaxial stress field, allows a reliable determination of a0. Furthermore, ion irradiation was shown to be a powerful method for stress relaxation, providing a stress-free lattice parameter solely linked to chemical effects.
SrFeO
3
nanoparticles-dispersed SrMoO4 insulating thin films deposited from Sr2FeMoO6 target in oxygen atmosphere
Authors: Kim Dal-Young , Kim Jin Soo , Park Bae Ho , Lee Jeon-Kook , Kim Jang Hee , Lee Je Hyun , Chang Joonyeon , Kim Hi-Jung , Kim Inyoung , Park Yun D.
Published: June 2004

Dielectric SrMoO4 thin films were deposited from Sr2FeMoO6 target in oxygen atmosphere, showing obvious M–H hysteresis loops at room temperature. It was revealed by transmission electron microscopy that SrFeO3 nanoparticles are dispersed in the SrMoO4 grains, to which the hystersis loops of the thin films are ascribed. This SrMoO4 thin film can be useful as a barrier material for Sr2FeMoO6-based devices, owing to easy fabrication process and compatibility with Sr2FeMoO6. Magnetic SrFeO3 nanoparticles are expected to enhance tunneling magnetoresistance.
Hard metallic glass of tungsten-based alloy
Authors: Ohtsuki M. , Tamura R. , Takeuchi S. , Yoda S. , Ohmura T.
Published: June 2004

A tungsten-based ductile metallic glass with the composition W46Ru37B17 was produced by a single-roller melt-spinning procedure. The differential scanning calorimetry measurement showed a two-step crystallization with the first crystallization temperature as high as 1174 K. Young’s modulus of the glass at room temperature was estimated to be 309±20 GPa by a nanoindentation test and the Vickers hardness at room temperature was 16.8±1 GPa. These values are higher than those of any metallic glasses so far reported. High-temperature Vickers hardness test indicated that the hardness value is higher than 10 GPa up to 900 K.
Properties of nitrogen-implanted p-type ZnO films grown on Si3N4/Si by radio-frequency magnetron sputtering
Authors: Lin Chin-Ching , Chen San-Yuan , Cheng Syh-Yuh , Lee Hsin-Yi
Published: June 2004

An nitrogen-implanted p-type ZnO film has been grown on a Si substrate buffered with Si3N4 using radio-frequency magnetron sputtering. The Si3N4 buffer layer can effectively improve film stoichiometry and reduce the formation of oxygen vacancies compared to ZnO on Si. The electrical properties of the p-type ZnO films implanted with 5×1012–1×1014 cm−2 N+ dose show a hole concentration of 5.0×1016–7.3×1017 cm−3, hole mobility of 2.51–6.02 cm2/V s, and resistivity of 10.11–15.3 Ω cm. The p-type ZnO films also showed an excellent crystallinity and a strong ultraviolet emission peak near 3.30 eV at room temperature. Moreover, as evidenced by extended x-ray absorption fine structure analysis, the local structure of the p-type ZnO films was changed due to the substitution of nitrogen ions for oxygen ions in p-type ZnO films. Our finding of p-type ZnO films grown on a Si3N4/Si substrate could provide a simple method to fabricate reproducible p-type ZnO films on silicon substrate for the development of large-scale optoelectronic integration device.
Bi modification for low-temperature processing of YMnO3 thin films
Authors: Choi Taekjib , Lee Jaichan
Published: June 2004

YMnO 3 thin films have been modified by Bi for low-temperature processing. YMnO3 thin-film growth typically requires high temperatures possibly leading to undesirable interface reaction and device failure in further processing. We have proposed Bi modification into YMnO3 (YBM) thin films grown on Si (100) by pulsed-laser deposition for reduced temperature processing. The growth temperature of YBM films was significantly reduced by more than 150 °C from the typical growth temperature of YMnO3 films. Highly c-axis-oriented growth of hexagonal YBM films at low temperatures was effective above 5% Bi content modification. Surface analysis on YBM films suggests that very thin Bi oxide layer forms on the topmost growing surface of YBM films and enhances the surface mobility of adatoms, leading to enhanced crystallization and low-temperature processing. The Bi modification did not deteriorate the electrical properties of YMnO3 such as dielectric constant and leakage current. This Bi modification can be an effective method to reduce processing temperature for other oxide thin films in physical vapor deposition.
Convergence in hydraulic architecture, water relations and primary productivity amongst habitats and across seasons in Sydney
Authors: Macinnis-Ng Catriona , McClenahan Kate , Eamus Derek
Published: June 2004

Convergence in leaf traits across biomes demonstrates generality in plant functioning. Relationships between hydraulic architecture and photosynthesis are less well studied. We investigated convergence in minimum leaf water potential (Ψmin), conductivity per sapwood area (ks), Huber value (Hv) and xylem embolism and photosynthesis in four habitats across two seasons (summer and winter) in the Sydney region in heathland, woodland (ridge-top), woodland (below-ridge) and mangrove. Seasonality strongly influenced all parameters in all habitats. Winter Ψmin values were lower than those for summer in the heathland and both woodland habitats but summer Ψmin values were lower than those for winter in the mangrove. Summer ks values were higher than winter values in all habitats, while Hv was higher in winter than summer for all habitats. Loss of conductance due to xylem embolism was larger in summer than winter in eight of 11 species. We also investigated relationships between the hydraulic parameters across habitats. There was a strong, significant inverse correlation between log-transformed Hv and log-transformed ks, which held across the seasons. There were significant inverse correlations between Ψmin and xylem embolism, which held within seasons but not across seasons. We found a strong, significant positive correlation between ks and Ψmin also within seasons but not across seasons and a significant negative correlation between xylem embolism and ks for winter but only a weak negative correlation between xylem embolism and ks for summer. We believe the seasonal patterns and relationships in hydraulic architecture and water relations are driven by the cost of efficient sapwood. This is demonstrated by the negative correlation between photosynthetic rate and ks in winter.
Leaf water use efficiency differs between Eucalyptus seedlings from contrasting rainfall environments
Authors: Searson Matthew J. , Thomas Dane S. , Montagu Kelvin D. , Conroy Jann P.
Published: June 2004

This study investigates the putative role of thicker leaves in enhancing photosynthetic capacity and water-use efficiency (WUE) of Eucalyptus species native to xeric environments. Three Eucalyptus species, Eucalyptus grandis Hill. (ex Maiden), E. sideroxylon Cunn. (ex Woolls) and E. occidentalis (Endl.), were grown under well-watered or water-limited conditions in a single compartment of a temperature-controlled glasshouse. Eucalyptus grandis is native to a mesic environment while E. sideroxylon and E. occidentalis are native to xeric environments. Leaves of E. sideroxylon and E. occidentalis were thicker and contained more nitrogen (N) on a leaf-area basis than E. grandis. Leaf gas-exchange measurements indicated that the photosynthetic capacity of E. sideroxylon and E.�occidentalis was greater than E. grandis and that stomatal conductance and WUE were negatively correlated. Whole-plant, gas-exchange and carbon-isotope measurements showed that E. sideroxylon and E. occidentalis had lower WUE than E. grandis under both well-watered and water-limited conditions. However, there was no difference in N-use efficiency between species. We suggest that stomatal conductance and leaf N content are functionally linked in these seedlings and conclude that thick leaves can, in some conditions, result in low WUE.
Rooting depth and plant water relations explain species distribution patterns within a sandplain landscape
Authors: Groom Philip K.
Published: June 2004

Tree and shrub species of the Banksia woodlands on the sandplains of northern Swan Coastal Plain, Western Australia possess a range of strategies to avoid or tolerate soil water deficits during the annual summer drought. Shallow-rooted shrub species (< 1 m rooting depth) inhabit a range of locations in the landscape, from top of dune crests to wetland embankments. These are the most drought-tolerant of all sandplain species, surviving extremely low summer soil water potentials (< –7 MPa) and tissue water deficits by significantly reducing their transpirational water loss (< 0.2 mmol m–2 s–1). This is in contrast to the few shallow-rooted species restricted to low-lying or seasonally waterlogged areas which are reliant on subsurface soil moisture or groundwater to maintain their relatively high summer water use. Recent studies of water source usage of selected Banksia tree species have shown that these deep-rooted species access groundwater up to a maximum depth of 9 m depth during the summer months, or soil moisture at depth when groundwater was greater than maximum rooting depths, depending on the species. Medium- and deep-rooted (1–2 m and > 2 m, respectively) shrub species cope with the summer soil drying phase and related decrease in groundwater levels by conserving leaf water loss and incurring predawn water potentials between –1 and –4 MPa, enabling them to occur over a range of topographic positions within the sandplain landscape.
Screening broad beans (Vicia faba) for magnesium deficiency. I. Growth characteristics, visual deficiency symptoms and plant nutritional status
Authors: Hariadi Yuda , Shabala Sergey
Published: June 2004

We used broad beans (Vicia faba L.) as a case study to characterise the development of magnesium (Mg) deficiency symptoms in plants and make a comparative evaluation of the suitability of various physiological characteristics as prospective tools for early diagnosis of Mg deficiency. Growth characteristics were measured at monthly intervals from plants grown in soil solution with a wide range of Mg concentrations (from 1 to 200 ppm). The data were then correlated with plant yield responses, pigment composition and nutrient content in leaves, as well as with visual deficiency symptoms. At the age of 4 weeks, no visual symptoms of deficiency were evident even for plants grown at 1 ppm (severe Mg deficiency). Shoot growth characteristics were very similar for a wide range of treatments, although a pronounced difference in plant yield was observed at the end of the experiment. It appears that neither plant biomass nor leaf area are good indicators for use as diagnostic tools for detection of Mg deficiency in broad beans. Although pigment analysis revealed some difference between treatments, at no age was it possible to distinguish between moderately Mg-deficient (10 or 20 ppm) and sufficient (50–80 ppm) treatments. Leaf elemental analysis for Mg content remained the most sensitive and accurate indicator of Mg deficiency in broad beans. However, it is unsuitable for screening purposes as it is both costly and time-consuming. There is a need for less expensive but effective, rapid screening tools of Mg deficiency in crops at early stages of plant ontogeny.
Screening broad beans (Vicia faba) for magnesium deficiency. II.Photosynthetic performance and leaf bioelectrical responses
Authors: Hariadi Yuda , Shabala Sergey
Published: June 2004

In search of rapid screening tools for magnesium (Mg) deficiency in crops at early stages of plant ontogeny, we studied the kinetics of leaf photosynthetic responses and changes in electrophysiological characteristics of broad bean leaves as affected by different levels of Mg in the nutrient solution (1–200 ppm). No apparent correlation between plant age, Mg supply level, leaf stomatal conductance (gs) and transpiration rate (E) were found. A significant difference in CO2 assimilation became obvious only at week 8. Chlorophyll fluorescence analysis, however, revealed a significant difference in the maximal quantum efficiency of PSII (Fv / Fm ratio) between Mg-deficient and Mg-sufficient plants as early as 2 weeks after seedling emergence. The most sensitive measurements were of light-induced changes in the leaf surface electric potential, with an almost 2-fold difference in the magnitude of leaf bioelectric response between 10 ppm (deficient) and 50 ppm (optimal) treatments. Preliminary experiments in which net Mg2+ fluxes were measured using the non-invasive ion flux estimation (MIFE) technique showed that the electrical changes on the leaf surface might, to some extent, reflect the movement of Mg2+ across the plasma membrane.
Pigment dynamics during cold-induced photoinhibition of Acacia melanoxylon
Authors: Watson Tim L. , Close Dugald C. , Davidson Neil J. , Davies Noel W.
Published: June 2004

Long-term acclimation of photo- and pigment-chemistry was investigated in a naturally-regenerating stand of Acacia melanoxylon R.Br. ex Ait. A pronounced decrease in photochemical efficiency of A. melanoxylon saplings was observed between autumn and winter in both thinned and unthinned treatments, but the decrease was more severe in the thinned treatment. Associated pigment changes in the unthinned treatment included a decrease in total chlorophyll content and a rise in chlorophyll a : b. Similar acclimation occurred in the thinned treatment with additional increase in zeaxanthin per unit chlorophyll observed. Saplings in the thinned treatment were exposed to lower minimum temperatures, more hours of frost and higher light intensities in the mid- to lower-crown. Growth chamber studies of the short-term acclimation of photo- and pigment-chemistry were conducted in a low / high light and cold / warm temperature factorial experiment. Photochemical efficiency and quantum yield adjusted within one day and then remained constant for 10 d in response to the imposed treatments. Chlorophyll concentration had decreased in all treatments by day 2 in the growth chambers, and subsequently increased in warm, but not in cold, treatments, irrespective of light level by day 10 in the growth chambers. The concentration of lutein-5,6-epoxide decreased in response to the cold-high light treatment and increased in response to other treatments by day 10 in the growth chambers, consistent with a function in sustained photoprotection in leaves of shade-adapted species. Our experiments indicated that A. melanoxylon is susceptible to cold-induced photoinhibition under cool temperatures (2–8°C) and moderate light intensities (450 μmol m–2 s–1).
Evolution of plant water relations research in Australia
Authors: Doley David
Published: June 2004

Ecophysiological research in Australia has focussed, at different times, on the fundamental similarities in function between all plant species, and on the peculiarity of Australian species with respect to their survival in stressful environments. Early work on plant water relations emphasised the differences between species, and indicated that diverse structural and functional attributes occurred in species from the same water-limited environment. Most recent research has emphasised processes that optimise rates of carbon dioxide exchange, but the understanding of functioning in plants with different morphological arrangements is incomplete. Variation in functions between individual plants and geographic populations in wild species has been examined to a lesser extent. The great variety within and between populations of wild plant species warrants further study for both understanding and more effective management of this biological resource.
The impacts of leaf shape and arrangement on light interception and potential photosynthesis in southern beech (Nothofagus cunninghamii)
Authors: Kern Stephen O. , Hovenden Mark J. , Jordan Gregory J.
Published: June 2004

The impact of differences in leaf shape, size and arrangement on the efficiency of light interception, and in particular the avoidance of photoinhibition, are poorly understood. We therefore estimated light exposure of branches in the cool temperate rainforest tree, Nothofagus cunninghamii (Hook.) Oerst., in which leaf shape, size and arrangement vary systematically with altitude and geographic origin. Measurements of incident photosynthetic photon flux density (PPFD) were made in the laboratory at solar angles corresponding to noon at summer solstice, winter solstice and equinox on branches collected from a common garden experiment. Tasmanian plants showed more self-shading than Victorian plants in summer and equinox. This was related to branch angle, leaf arrangement and leaf shape. Using a modelled light response-curve, we estimated the carbon assimilation rate and the flux density of excess photons at different incident PPFD. Victorian plants had higher predicted assimilation rates than Tasmanian plants in summer and equinox, but were exposed to substantially greater levels of excess photons. Because of the shape of the light-response curve, self-shading appears to reduce the plant's exposure to excess photons, thus providing photoprotection, without substantially reducing the carbon assimilation rate. This is dependent on both regional origin and season.
Short Communication: Leaf trait relationships in Australian plant species
Authors: Wright Ian J. , Groom Philip K. , Lamont Byron B. , Poot Pieter , Prior Lynda D. , Reich Peter B. , Schulze E-Detlef , Veneklaas Erik J. , Westoby Mark
Published: June 2004

Leaf trait data were compiled for 258 Australian plant species from several habitat types dominated by woody perennials. Specific leaf area (SLA), photosynthetic capacity, dark respiration rate and leaf nitrogen (N) and phosphorus (P) concentrations were positively correlated with one another and negatively correlated with average leaf lifespan. These trait relationships were consistent with previous results from global datasets. Together, these traits form a spectrum of variation running from species with cheap but frequently replaced leaves to those with strategies more attuned to a nutrient-conserving lifestyle. Australian species tended to have SLAs at the lower end of the spectrum, as expected in a dataset dominated by sclerophyllous species from low fertility or low rainfall sites. The existence of broad-scale, 'global' relationships does not imply that the same trait relationships will always be observed in small datasets. In particular, the probability of observing concordant patterns depends on the range of trait variation in a dataset, which, itself, may vary with sample size or species-sampling properties such as the range of growth forms, plant functional 'types', or taxa included in a particular study. The considerable scatter seen in these broad-scale trait relationships may be associated with climate, physiology and phylogeny.
Research Note: Measuring variability in chlorophyll-fluorescence-derived photosynthetic parameters in situ with a programmable multi-channel fluorometer
Authors: Runcie John W. , Riddle Martin J.
Published: June 2004

A submersible device was constructed for simultaneous in situ measurement of the effective quantum yield of chlorophyll fluorescence (ΔF / Fm′) of eight macroalgal samples. The device incorporated a commercially available PAM fluorometer. Four samples each of the macroalgae Iridaea mawsonii (Lucas) and Monostroma hariotii (Gain) were examined. ΔF / Fm′ and light-response curves (LCs) were regularly applied over 24 h to estimate diel changes in relative electron transport rates and the relative efficiency of photon conversion at low irradiances (α), and the variance attributable to mean values of both ΔF / Fm′ and α were estimated. A second commercial single-channel fluorometer provided an independent measure of variability in LC parameters between individual samples, and the magnitude of this variability was within the range measured with the multi-channel device. Between-sample variability at noon, measured with the multi-channel device, was significantly greater than at other times of the day. ΔF / Fm′ of M. hariotii were not significantly different throughout most of the day except at midnight, when values were significantly higher. In contrast, over 24-h only ΔF / Fm′ of I. mawsonii at noon (growing in low light) was significantly lower. By providing replicate LCs at each time point, the programmable multi-channel fluorometer enables testing of significant differences in photosynthetic parameters over a diel period.
Cassowary frugivory, seed defleshing and fruit fly infestation influence the transition from seed to seedling in the rare Australian rainforest tree, Ryparosa sp. nov. 1 (Achariaceae)
Authors: Webber Bruce L. , Woodrow Ian E.
Published: June 2004

The rare Australian rainforest tree Ryparosa sp. nov. 1 aff. javanica (sensu Webber & Curtis, BW-017; Achariaceae) has large fleshy fruits that undergo a distinctive colour change during ripening. Fruit seem highly suited to frugivore interactions with large ground-dwelling avian or marsupial frugivores, a role primarily filled by the endangered cassowary. We found that fruits had chemical defence traits that closely paralleled morphological ripening signals. Young fruit seeds had amongst the highest concentrations of plant tissue cyanogens ever recorded (some in excess of 12 mg g–1 dw), yet the flesh of ripe fruits had negligible cyanogen defence. A seed treatment trial found that cassowary gut passage significantly improved germination from 4% to 92%, and we were not able to replicate this result with simulated treatments. While high levels of fruit fly larval infestation accounted for reduced seed viability, this predation was apparently reduced by cassowary gut passage. Post-germination seedling traits such as haustorial cryptocotylar cotyledons and epigeal germination may increase the chance of survival for establishing seedlings. We conclude that the range of traits seen in Ryparosa recruitment is particularly suited to interactions with frugivores and survival in a rainforest ecosystem.
Viewpoint: Assessing the carbon sequestration potential of mesic savannas in the Northern Territory, Australia: approaches, uncertainties and potential impacts of fire
Authors: Williams Richard J. , Hutley Lindsay B. , Cook Garry D. , Russell-Smith Jeremy , Edwards Andrew , Chen Xiayong
Published: June 2004

Tropical savannas cover a quarter of the Australian landmass and the biome represents a significant potential carbon sink. However, these savannas are subject to frequent and extensive fire. Fire regimes are likely to affect the productivity and carbon sequestration potential of savannas, through effects on both biomass and carbon emissions. The carbon sequestration potential has been estimated for some savanna sites by quantifying carbon storage in biomass and soil pools, and the fluxes to these pools. Using different techniques, previous work in these savannas has indicated that net ecosystem productivity [NEP, net primary productivity (NPP) less heterotrophic respiration] was about –3 t C ha–1 y–1 (i.e. a carbon sink). However, the impacts of fire were not accounted for in these calculations. Estimates of NEP have been combined with remotely-sensed estimates of area burnt and associated emissions for an extensive area of mesic savanna in Arnhem Land, NT, Australia. Combining NEP estimates with precise fire data provides an estimate of net biome productivity (NBP), a production index that includes carbon loss through disturbance (fire), and is thus a more realistic indicator of sequestration rate from this biome. This preliminary analysis suggests that NBP is approximately –1 t C ha–1 y–1 (i.e. a carbon sink). A reduction in the annual area burnt is likely to increase the sink size. Uncertainties surrounding these estimates of NBP and the implications of these uncertainties for land management in these extensive landscapes are discussed.
Terpene deployment in Eucalyptus polybractea; relationships with leafstructure, environmental stresses, and growth
Authors: King Drew J. , Gleadow Roslyn M. , Woodrow Ian E.
Published: June 2004

Terpene deployment was examined in a population of Eucalyptus polybractea (R.Baker) trees. Eucalyptus polybractea is a terpene-accumulating species, which stores terpenes in oil glands beneath the leaf surface. Using regression analysis, we showed that leaf thickness, measured as leaf mass per area (LMA), influenced terpene content, apparently through regulation of gland dimensions, and thus, gland volume. We also examined how environmental factors affected terpene content through regulation of both LMA, and therefore, storage capacity, and the supply of resources for terpene synthesis. Neither water stress, measured using carbon isotope ratios as an indicator, nor nutrient stress, measured as foliar nitrogen and phosphorus content, accounted for observed variation in either terpene content or LMA. Phenolic content, measured as a possible competing carbon sink, did not account for variation in terpene content, and variation in environmental stresses could not account for differences in growth rate. However, both terpenes and total carbon-based secondary metabolites (terpenes and phenolics) showed positive correlations with growth, suggesting plants gain a growth advantage by deploying greater amounts of secondary metabolites.
Cyanogenesis in tropical Prunus turneriana: characterisation, variation and response to low light
Authors: Miller Rebecca E. , Gleadow Roslyn M. , Woodrow Ian E.
Published: June 2004

This study characterised three aspects of cyanogenesis in the late successional tropical rainforest species Prunus turneriana (F.M.Bailey) Kalkman. First, all tissues were found to be highly cyanogenic, containing combinations of the cyanogenic glycosides (R)-prunasin, (S)-sambunigrin, and amygdalin. Second, the progeny of a single parent tree varied markedly and continuously in their cyanogenic glycoside content, indicating that this variation is genetically based. Third, we investigated resource allocation to cyanogenic glycosides in light treatments representative of rainforest understorey and gap environments. Contrary to our hypothesis that under low light, photosynthetic gain would be maximised by the reallocation of nitrogen from defence to the photosynthetic system, we found no difference in cyanogenic glycoside concentration, or the proportion of nitrogen allocated to cyanogenic glycoside, between high and low light. However, within the plant, shade affected a significant change in distribution of cyanogenic glycosides between young and old leaves. There was an increased allocation of cyanogenic glycosides to old, expanded and photosynthetically productive leaves, a pattern which appears inconsistent with predictions of optimal defence theories, and the results of other studies. We suggest that such a strategy may be advantageous for seedlings of tree species that can only reach a reproductive stage following the creation of a canopy gap.
Seasonal responses of xylem sap velocity to VPD and solar radiation during drought in a stand of native trees in temperate Australia
Authors: Zeppel Melanie J. B. , Murray Brad R. , Barton Craig , Eamus Derek
Published: June 2004

Xylem sap velocity of two dominant tree species, Eucalyptus crebra F. Muell. and Callitris glaucophylla J. Thompson & L.A.S. Johnson, in a native remnant forest of eastern Australia was measured in winter and summer during a prolonged (> 12 months) and extensive drought. The influence of vapour pressure deficit (VPD) and solar radiation levels on the velocity of sap was determined. Pronounced hysteresis in sap velocity was observed in both species as a function of VPD and solar radiation. However, the rotation of the hysteresis curve was clockwise for the response of sap velocity to VPD but anti-clockwise in the response of sap velocity to radiation levels. A possible reason for this difference is discussed.The degree of hysteresis (area bounded by the curve) was larger for the VPD response than the response to solar radiation and also varied with season. A simple linear model was able to predict sap velocity from knowledge of VPD and solar radiation in winter and summer. The consistent presence of hysteresis in the response to sap velocity to VPD and solar radiation suggests that large temporal and spatial models of vegetation water use may require some provision for the different responses of sap velocity, and hence water use, to VPD and solar radiation, between morning and afternoon and between seasons.
Nitrogen ecophysiology of Heron Island, a subtropical coral cay of the Great Barrier Reef, Australia
Authors: Schmidt Susanne , Dennison William C. , Moss Gordon J. , Stewart George R.
Published: June 2004

Coral cays form part of the Australian Great Barrier Reef. Coral cays with high densities of seabirds are areas of extreme nitrogen (N) enrichment with deposition rates of up to 1000 kg N ha–1 y–1. The ways in which N sources are utilised by coral cay plants, N is distributed within the cay, and whether or not seabird-derived N moves from cay to surrounding marine environments were investigated. We used N metabolite analysis, 15N labelling and 15N natural abundance (δ15N) techniques. Deposited guano-derived uric acid is hydrolysed to ammonium (NH4+) and gaseous ammonia (NH3). Ammonium undergoes nitrification, and nitrate (NO3–) and NH4+ were the main forms of soluble N in the soil. Plants from seabird rookeries have a high capacity to take up and assimilate NH4+, are able to metabolise uric acid, but have low rates of NO3– uptake and assimilation. We concluded that NH4+ is the principal source of N for plants growing at seabird rookeries, and that the presence of NH4+ in soil and gaseous NH3 in the atmosphere inhibits assimilation of NO3–, although NO3– is taken up and stored. Seabird guano, Pisonia forest soil and vegetation were similarly enriched in 15N suggesting that the isotopic enrichment of guano (δ15N 9.9‰) carries through the forest ecosystem. Soil and plants from woodland and beach environments had lower δ15N (average 6.5‰) indicating a lower contribution of bird-derived N to the N nutrition of plants at these sites. The aquifer under the cay receives seabird-derived N leached from the cay and has high concentrations of 15N-enriched NO3– (δ15N�7.9‰). Macroalgae from reefs with and without seabirds had similar δ15N values of 2.0–3.9‰ suggesting that reef macroalgae do not utilise 15N-enriched seabird-derived N as a main source of N. At a site beyond the Heron Reef Crest, macroalgae had elevated δ15N of 5.2‰, possibly indicating that there are locations where macroalgae access isotopically enriched aquifer-derived N. Nitrogen relations of Heron Island vegetation are compared with other reef islands and a conceptual model is presented.
Differential plague-transmission dynamics determine
Yersinia pestis
population genetic structure on local, regional, and global scales
Authors: Girard Jessica M. , Wagner David M. , Vogler Amy J. , Keys Christine , Allender Christopher J. , Drickamer Lee C. , Keim Paul
Published: June 2004

Plague, the disease caused by the bacterium
Yersinia pestis
, has greatly impacted human civilization.
Y
.
pestis
is a successful global pathogen, with active foci on all continents except Australia and Antarctica. Because the
Y
.
pestis
genome is highly monomorphic, previous attempts to characterize the population genetic structure within a single focus have been largely unsuccessful. Here we report that highly mutable marker loci allow determination of
Y
.
pestis
population genetic structure and tracking of transmission patterns at two spatial scales within a single focus. In addition, we found that
in vitro
mutation rates for these loci are similar to those observed
in vivo
, which allowed us to develop a mutation-rate-based model to examine transmission mechanisms. Our model suggests there are two primary components of plague ecology: a rapid expansion phase for population growth and dispersal followed by a slower persistence phase. This pattern seems consistent across local, regional, and even global scales.
Nitric oxide (NO)-releasing statin derivatives, a class of drugs showing enhanced antiproliferative and antiinflammatory properties
Authors: Ongini Ennio , Impagnatiello Francesco , Bonazzi Albino , Guzzetta Massimiliano , Govoni Mirco , Monopoli Angela , Del Soldato Piero , Ignarro Louis J.
Published: June 2004

Inhibitors of 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) reductase, namely statins, exert pleiotropic actions beyond lipid-lowering effects. Their pharmacological activity on atherosclerotic plaque stability and vascular inflammation appears to be mediated, at least in part, by nitric oxide (NO). With the aim of enhancing the nonlipid-lowering properties of selected statins, we introduced a NO-releasing moiety into the structure of pravastatin (NCX 6550) and fluvastatin (NCX 6553). NO release was evaluated as nitrosylhemoglobin adduct formation by using EPR spectroscopy in rat blood. Both compounds produced a linear time-dependent increase in nitrosylhemoglobin formation, which is consistent with slow NO release kinetics. In PC12 cells, unlike their native statins, both compounds stimulated cGMP formation (NCX 6550, EC50= 2.3 ± 0.2 μM; NCX 6553, EC50= 2.7 ± 0.2 μM). Moreover, NCX 6550 potently inhibited cell proliferation in rat aortic smooth muscle cells (IC50= 2.2 ± 0.3 μM) with a mechanism that involved both the polyamine and HMG-CoA reductase signaling pathways. Hence, mevalonate or putrescine partially reverted the effects of NCX 6550 and their combination was fully effective. In RAW 264.7 murine macrophage cells stimulated with lipopolysaccharide (1 μg/ml), NCX 6550, but not pravastatin, significantly decreased inducible NO synthase and cyclooxygenase-2 protein expression as well as nitrite accumulation. All together, the data show that the previously undescribed NO-releasing statins retain HMG-CoA reductase inhibitory activity and release bioactive NO slowly. Among the additional properties, compared with native statins, the NO-releasing statins show enhanced antiinflammatory effects. Thus, NO-releasing statins represent an interesting class of drugs having potential in the therapy of disorders associated with endothelial dysfunction and vascular inflammation.
Recoverin Regulates Light-dependent Phosphodiesterase Activity in Retinal Rods
Authors: Makino Clint L. , Dodd R.L. , Chen J. , Burns M.E. , Roca A. , Simon M.I. , Baylor D.A.
Published: June 2004

The Ca2+-binding protein recoverin may regulate visual transduction in retinal rods and cones, but its functional role and mechanism of action remain controversial. We compared the photoresponses of rods from control mice and from mice in which the recoverin gene was knocked out. Our analysis indicates that Ca2+-recoverin prolongs the dark-adapted flash response and increases the rod's sensitivity to dim steady light. Knockout rods had faster Ca2+ dynamics, indicating that recoverin is a significant Ca2+ buffer in the outer segment, but incorporation of exogenous buffer did not restore wild-type behavior. We infer that Ca2+-recoverin potentiates light-triggered phosphodiesterase activity, probably by effectively prolonging the catalytic activity of photoexcited rhodopsin.
Antagonistic Regulation of Native Ca2+- and ATP-sensitive Cation Channels in Brain Capillaries by Nucleotides and Decavanadate
Authors: Csanády László , Adam-Vizi Vera
Published: June 2004

Regulation by cytosolic nucleotides of Ca2+- and ATP-sensitive nonselective cation channels (CA-NSCs) in rat brain capillary endothelial cells was studied in excised inside-out patches. Open probability (Po) was suppressed by cytosolic nucleotides with apparent KI values of 17, 9, and 2 μM for ATP, ADP, and AMP, as a consequence of high-affinity inhibition of channel opening rate and low-affinity stimulation of closing rate. Cytosolic [Ca2+] and voltage affected inhibition of Po, but not of opening rate, by ATP, suggesting that the conformation of the nucleotide binding site is influenced only by the state of the channel gate, not by that of the Ca2+ and voltage sensors. ATP inhibition was unaltered by channel rundown. Nucleotide structure affected inhibitory potency that was little sensitive to base substitutions, but was greatly diminished by 3′-5′ cyclization, removal of all phosphates, or complete omission of the base. In contrast, decavanadate potently (K1/2 = 90 nM) and robustly stimulated Po, and functionally competed with inhibitory nucleotides. From kinetic analyses we conclude that (a) ATP, ADP, and AMP bind to a common site; (b) inhibition by nucleotides occurs through simple reversible binding, as a consequence of tighter binding to the closed-channel relative to the open-channel conformation; (c) the conformation of the nucleotide binding site is not directly modulated by Ca2+ and voltage; (d) the differences in inhibitory potency of ATP, ADP, and AMP reflect their different affinities for the closed channel; and (e) though decavanadate is the only example found to date of a compound that stimulates Po with high affinity even in the presence of millimolar nucleotides, apparently by competing for the nucleotide binding site, a comparable mechanism might allow CA-NSC channels to open in living cells despite physiological levels of nucleotides. Decavanadate now provides a valuable tool for studying native CA-NSC channels and for screening cloned channels.
Regulation of KCNQ2/KCNQ3 Current by G Protein Cycling
Authors: Suh Byung-Chang , Horowitz Lisa F. , Hirdes Wiebke , Mackie Ken , Hille Bertil
Published: June 2004

Receptor-mediated modulation of KCNQ channels regulates neuronal excitability. This study concerns the kinetics and mechanism of M1 muscarinic receptor–mediated regulation of the cloned neuronal M channel, KCNQ2/KCNQ3 (Kv7.2/Kv7.3). Receptors, channels, various mutated G-protein subunits, and an optical probe for phosphatidylinositol 4,5-bisphosphate (PIP2) were coexpressed by transfection in tsA-201 cells, and the cells were studied by whole-cell patch clamp and by confocal microscopy. Constitutively active forms of Gαq and Gα11, but not Gα13, caused a loss of the plasma membrane PIP2 and a total tonic inhibition of the KCNQ current. There were no further changes upon addition of the muscarinic agonist oxotremorine-M (oxo-M). Expression of the regulator of G-protein signaling, RGS2, blocked PIP2 hydrolysis and current suppression by muscarinic stimulation, confirming that the Gq family of G-proteins is necessary. Dialysis with the competitive inhibitor GDPβS (1 mM) lengthened the time constant of inhibition sixfold, decreased the suppression of current, and decreased agonist sensitivity. Removal of intracellular Mg2+ slowed both the development and the recovery from muscarinic suppression. When combined with GDPβS, low intracellular Mg2+ nearly eliminated muscarinic inhibition. With nonhydrolyzable GTP analogs, current suppression developed spontaneously and muscarinic inhibition was enhanced. Such spontaneous suppression was antagonized by GDPβS or GTP or by expression of RGS2. These observations were successfully described by a kinetic model representing biochemical steps of the signaling cascade using published rate constants where available. The model supports the following sequence of events for this Gq-coupled signaling: A classical G-protein cycle, including competition for nucleotide-free G-protein by all nucleotide forms and an activation step requiring Mg2+, followed by G-protein–stimulated phospholipase C and hydrolysis of PIP2, and finally PIP2 dissociation from binding sites for inositol lipid on the channels so that KCNQ current was suppressed. Further experiments will be needed to refine some untested assumptions.
Characterization of theSaccharomyces cerevisiaeFol1 Protein: Starvation for C1 Carrier Induces Pseudohyphal Growth
Authors: Güldener Ulrich , Koehler Gabriele J. , Haussmann Christoph , Bacher Adelbert , Kricke Jörn , Becher Dietmar , Hegemann Johannes H.
Published: June 2004

Tetrahydrofolate (vitamin B9) and its folate derivatives are essential cofactors in one-carbon (C1) transfer reactions and absolutely required for the synthesis of a variety of different compounds including methionine and purines. Most plants, microbial eukaryotes, and prokaryotes synthesize folate de novo. We have characterized an important enzyme in this pathway, the Saccharomyces cerevisiae FOL1 gene. Expression of the budding yeast gene FOL1 in Escherichia coli identified the folate biosynthetic enzyme activities dihydroneopterin aldolase (DHNA), 7,8-dihydro-6-hydroxymethylpterin-pyrophosphokinase (HPPK), and dihydropteroate synthase (DHPS). All three enzyme activities were also detected in wild-type yeast strains, whereas fol1Δ deletion strains only showed background activities, thus demonstrating that Fol1p catalyzes three sequential steps of the tetrahydrofolate biosynthetic pathway and thus is the central enzyme of this pathway, which starting from GTP consists of seven enzymatic reactions in total. Fol1p is exclusively localized to mitochondria as shown by fluorescence microscopy and immune electronmicroscopy. FOL1 is an essential gene and the nongrowth phenotype of the fol1 deletion leads to a recessive auxotrophy for folinic acid (5′-formyltetrahydrofolate). Growth of the fol1Δ deletion strain on folinic acid–supplemented rich media induced a dimorphic switch with haploid invasive and filamentous pseudohyphal growth in the presence of glucose and ammonium, which are known suppressors of filamentous and invasive growth. The invasive growth phenotype induced by the depletion of C1 carrier is dependent on the transcription factor Ste12p and the flocullin/adhesin Flo11p, whereas the filamentation phenotype is independent of Ste12p, Tec1p, Phd1p, and Flo11p, suggesting other signaling pathways as well as other adhesion proteins.