bluuebunny/crossref_metadata_2025 huggingface dataset:
Palynological evidence for the Palaeocene evolution of the forearc basin, Indus Suture Zone, Ladakh, India
Authors: Upadhyay Rajeev , Ram‐Awatar  , Kar R. K. , Sinha Anshu K.
Published: July 2004

The discovery of Permian, Mesozoic and Palaeocene palynomorphs from the Nindam forearc basin, exposed along the Indus Suture Zone in Ladakh, is reported. The palynomorphs are from volcanogenic sandstones and are poorly preserved, distorted and show the effects of abrasion (striation marks). The frequent occurrence of Proxapertites indicates the assemblage is at least Palaeocene in age. The Palaeocene palynomorphs and sediments were transported to the Nindam trough from nearby elevated landward regions (islands). These Palaeocene provenance areas were characterized by an estuarine, nearshore, tropical, warm‐humid environment and were situated at equatorial palaeolatitudes. However, the occurrence of Permian and Mesozoic palynomorphs in the assemblage indicates that the Late Palaeozoic and Mesozoic Tethyan sedimentary rocks exposed along the northern margin of the Indian plate were redeposited into the tectonically active Cretaceous–Palaeocene trench–subduction complex that existed between the Indian and the Asian plates until the collision took place at ∼50–60 Ma.
Seed production of Chenopodium album in competition with field vegetables
Authors: Grundy A C , Mead A , Burston S , Overs T
Published: July 2004

Total weed control within a crop is both difficult and expensive to achieve, so that some weeds will often remain to set seed. The seed production resulting from these weeds will ultimately affect the sustainability of the weed control strategy. If too much is allowed to return each season there could be a gradual, but significant, increase in the potential weed flora over a number of seasons. Field trials were carried out in 2000 and 2001 to quantify the potential magnitude of this weed seed return from Chenopodium album L., grown at two planting densities either in pure stands or in competition with one of two crops (cabbage or onion). Crop and weed weights and weed seed production were notably greater in 2001. Both dry weight and seed production of C. album were suppressed by increasing planting density or by the presence of crop, with cabbage having a more suppressive effect. Despite the plasticity in seed production, a linear relationship was demonstrated between log weed seed production and log weed biomass that was robust over a range of competitive situations with onion and cabbage, at different planting densities and in growing seasons. The study also demonstrated that the relationship could be combined with an existing simple competition model to allow the consequences of incomplete weed control to be assessed in terms of potential weed seed return.
Effect of sowing date and host resistance on the establishment and development of Orobanche crenata in faba bean and common vetch
Authors: Pérez‐de‐Luque A , Sillero J C , Moral A , Cubero J I , Rubiales D
Published: July 2004

The effect of early and late sowing dates on the establishment of Orobanche crenata Forsk. (crenate broomrape) in resistant and susceptible cultivars of faba bean (Vicia faba L.) and vetch (Vicia sativa L.) were studied over four seasons in southern Spain. Differences in establishment, development and shoot emergence of the parasite were compared. With resistant faba bean and vetch cultivars, there was reduced attachment and shoot emergence of O. crenata with all sowing dates. Susceptible cultivars were more severely affected by the parasite with early sowing. Orobanche crenata development was also delayed in resistant cultivars. Crop yield, estimated by the number of pods per plant, decreased with late sowings. The combined use of resistant cultivars and early sowing is a useful tool as part of an integrated control strategy. Resistant cultivars allow early sowing (with low O. crenata attack), thus avoiding yield losses due to the short crop cycle with late sowing.
An investigation of genetic variation in Cirsium arvense field patches
Authors: Hettwer U , Gerowitt B
Published: July 2004

The genetic structure of typical Cirsium arvense patch populations in two arable fields was examined. Patches were mapped and plant samples were taken in these patches. Plants of a central patch and four surrounding patches were sampled in 1 year to investigate the influence of root fragment dispersal. Plants of another patch were sampled in three subsequent years to investigate the patch development. The genotypes of the plants were examined using repetitive enterogenic primer (REP) and inter simple sequence repeat (ISSR) analysis. The mean proportion of distinguishable genotypes ranged from 0.13 to 0.67 and the evenness index ranged from 0.58 to 1.00. Differences in genotypes between neighbouring patches indicated that root fragment dispersal via soil cultivation was of minor importance. Three years sampling within a patch showed that the patch mainly ‘grew’ via the establishment of new clones rather than by clonal growth of one genotype. The influence of various factors caused by population demography or arable practice on patch development in an arable field is discussed. Although various factors can help to maintain genetic diversity, there is strong evidence for regular seedling establishment in arable fields.
Solid substrate for production of Alternaria alternata conidia: a potential mycoherbicide for the control of Eichhornia crassipes (water hyacinth)
Authors: Babu RM , Sajeena A , Seetharaman K
Published: July 2004

Eichhornia crassipes (water hyacinth), a major aquatic weed in India, is one of the targets in a biological weed control research programme in India. A fungal pathogen, Alternaria alternata, is being evaluated as a biological control agent for this weed. The feasibility of solid substrate for the mass production of A. alternata has been examined. Conidia production and virulence of A. alternata were affected by temperature, light and incubation period. The highest number of conidia were produced on rice seed followed by wheat, sorghum, maize seeds and cornmeal at 20°C when exposed to near‐ultraviolet than on the other substrates, while the least conidia were observed on these substrates under light conditions. At 20°C, large numbers of virulent conidia were produced on rice seeds after 4 weeks of incubation under constant dark conditions. Henceforth, the use of rice seeds as a solid substrate for production of A. alternata could be a feasible method to produce conidia in a village co‐operative scenario in India.
Effect of weed control treatments on weeds, seed yield, yield components and nodulation in winter lentil
Authors: Erman M , Tepe I , Yazlik A , Levent R , Ipek K
Published: July 2004

Good weed control is critical in winter lentil production. This study was conducted on the lentil cultivar Sazak 91 during the winter seasons of 1997–98 and 1998–99 to determine the most appropriate method for controlling weeds. Hand weeding (weed‐free control), weedy control (inoculated), weedy control (uninoculated), hand hoeing once, hand hoeing twice, trifluralin, imazethapyr, linuron, prometryn, phenmedipham + desmedipham, trifluralin + hand hoeing and linuron + hand hoeing treatments were evaluated and the effects of herbicides on nodulation in lentil were investigated. In the first year Convolvulus arvensis, Centaurea balsamita, Ranunculus arvensis, Cephalaria syriaca and Lathyrus spp., dominated whereas in the second year Hordeum vulgare, Adonis aestivalis and Centaurea depressa were the dominant weed species in the plots. Prometryn, hand hoeing, linuron and a combination of linuron + hand hoeing were found to be the most effective for control of weeds, resulting in the highest yield in winter lentil throughout the investigation. Trifluralin and imazethapyr had a phytotoxic effect on the lentil plants. None of the weed control treatments had any adverse effects on nodulation and Rhizobium leguminosarum inoculation was not found to have any effect on the competitive ability of the lentil plants.
Effects of oxadiargyl on direct‐seeded rice and Echinochloa crus‐galli under aerobic and anaerobic conditions
Authors: Gitsopoulos T K , Froud‐Williams R J
Published: July 2004

Dose–response experiments were conducted in glasshouse pot experiments to investigate the selectivity of oxadiargyl, a recently introduced herbicide, in direct‐seeded rice under both aerobic and anaerobic conditions. Crop sensitivity to oxadiargyl was comparatively greater for wet‐seeded (anaerobic) than for dry‐seeded rice (aerobic). Likewise, greater efficacy against Echinochloa crus‐galli (L.) was also observed under anaerobic conditions. These results indicate greater activity of oxadiargyl under anaerobic conditions, but that application pre‐sowing with subsequent flooding would reduce selectivity in wet‐seeded rice. The results are discussed in relation to rice production in Mediterranean agriculture.
The glutamate dehydrogenase gene gdhA increased the resistance of tobacco to glufosinate
Authors: Nolte S A , Young B G , Mungur R , Lightfoot D A
Published: July 2004

The gene gdhA from Escherichia coli, that encodes a NADPH‐dependent glutamate dehydrogenase (GDH), directs a novel pathway in transgenic plants that allows an increase in ammonium assimilation. Glufosinate leads to plant death by the irreversible inhibition of glutamate synthetase (GS) leading to a disruption of subsequent GS‐related processes resulting in elevated ammonium and disruption of photorespiration. Therefore, it was speculated that the gdhA‐transformed plants may exhibit a novel mechanism of resistance to glufosinate by altered activity of the GDH‐directed pathway(s) and subsequently related processes. Studies were conducted in the greenhouse to evaluate the resistance of tobacco plants containing the gdhA gene to glufosinate. Five tobacco genotype lines were investigated including a non‐transformed control line, a positive control line and three transformed lines with levels of increasing GDH activity directed by the gdhA gene. Plants transformed with the gdhA gene expressed up to six times increased level of resistance (GR50) to glufosinate compared with the non‐transformed control, which is 100 times less resistant than plants transformed with the bar gene. The GDH activity among lines was highly correlated (r2 = 0.9903) with the level of herbicide resistance. Thus, the use of the E. coli gdhA gene in plant transformations can provide an additional mechanism for resistance to glufosinate.
The Wilderness Society's WildCountry Program
Authors: McDonald Tein
Published: July 2004

The WildCountry program boldly aims to offer ‘a future for Australia's wilderness and biodiversity throughout and beyond the 21st Century’. This is to be achieved through building partnerships — one of the most important being a formal partnership with ecologists.
Estimating population abundance in plant species with dormant life‐stages: Fire and the endangered plant Grevillea caleyi R. Br.
Authors: Auld Tony D. , Scott Judith
Published: July 2004

Summary  Assessment of the conservation significance of a species at a particular site involves estimating the population size. Generally this is based on a single survey. However, where plant species vary greatly in abundance in response to disturbance regimes, there will be uncertainty associated with the use of single estimates of abundance. The interpretation of such estimates is dependent on an understanding of the ecology of the species and the disturbance regimes that impact on it. We examined the usefulness of abundance estimates in the endangered shrub Grevillea caleyi (a fire‐sensitive shrub with a persistent soil seed bank) from south‐eastern Australia, where fire is a major landscape disturbance. Comparisons of estimates of abundance before and after fire showed very large changes in the number of plants of G. caleyi above ground. Changes in abundance of over two orders of magnitude were observed. The longer the site was left unburnt, the greater the magnitude of change in abundance after the next fire. Above‐ground plants may be rare or absent at sites unburnt for over 15–20 years, but were abundant after fire, due to re‐establishment from the soil seed bank. Sites burnt by two fires in quick succession showed declines in population abundance, most likely due to the soil seed bank not being replenished between such short interval fires. Assessments of the conservation significance of remnant sites of G. caleyi and similar species based on a single sample of above‐ground plant abundance at one time are considered inappropriate. The amount of available habitat for G. caleyi, either as area of occupancy or preferably extent of available habitat, was a moderate predictor of the likely magnitude of abundance in the species after fire. However, the usefulness of these measures for species whose biology is comparable to Grevillea caleyi, will be limited due to factors relating to the degree of species‐specific habitat requirements, local site fire history and the impact of any one fire on resultant post‐fire germination levels. Any assessment of conservation significance will require the interpretation of available information in relation to the ecology of a species.
An algorithm for computing the asymptotic fisher information matrix for seasonal SISO models
Authors: Klein André , Mélard Guy
Published: July 2004

Abstract.  The paper presents an algorithm for computing the asymptotic Fisher information matrix of a possibly seasonal single‐input single‐output (SISO) time‐series model. That matrix is a block matrix whose elements are basically integrals of rational functions over the oriented unit circle. The procedure makes use of the autocovariance or the cross‐covariance function of two autoregressive processes based on the same noise. The algorithm also works when the input variable is omitted, the case of a seasonal ARMA model.
A joint test of fractional integration and structural breaks at a known period of time
Authors: Gil‐Alana Luis A.
Published: July 2004

Abstract.  We propose the use of a version of the tests of Robinson [Journal of the American Statistical Association, 89 (1994) 1420] for testing the order of integration in raw time series in the presence of structural breaks at known periods of time. Also, a joint test for simultaneously testing the degree of integration and the need for the break is developed. Several Monte Carlo experiments conducted in the paper show that the joint test has better size and power properties relative to Robinson's (1994) tests. The tests are applied to the annual structure of the US real GDP, the results showing that the series is I(d) with d≥1, and with a break due to the World War II.
Maximum quasi‐likelihood estimation for the near(2) model
Authors: Perera S.
Published: July 2004

Abstract. Maximum quasi‐likelihood estimation is investigated for the NEAR(2) model, an autoregressive time series model with marginal exponential distributions. In certain regions of the parameter space, simulations indicate that maximum quasi‐likelihood estimators perform better than two‐stage conditional least squares estimators in terms of the per cent of estimates falling in the parameter space. The problem of out‐of‐range estimates is shown to be caused by the lack of information in the data rather than the characteristics of the method of estimation.
INFLUENCE OF ULTRAVIOLET RADIATION ON THE EXPRESSION OF PROLIFERATING CELL NUCLEAR ANTIGEN AND DNA POLYMERASE α IN SKELETONEMA COSTATUM (BACILLARIOPHYCEAE)1
Authors: Wei Su Fen , Hwang Sheng‐Ping L. , Chang Jeng
Published: July 2004

To evaluate the effects of UV radiation on the expression of DNA replication‐related genes in phytoplankton, the mRNA levels of DNA polymerase α and proliferating cell nuclear antigen (PCNA) in a marine diatom, Skeletonema costatum (Greville) Cleve, were studied using the methods of real‐time quantitative PCR. Treating the algal cultures with UVC radiation for 15 min caused severe mortality during the 24‐h period after treatment. A significant amount of thymine dimers was detected in the treated cultures, and the mRNA levels of DNA polymerase α and PCNA increased by as much as 140 and 23 pmol·(g total RNA)−1, respectively, compared with the control experiments. In contrast, massive cell deaths did not occur in cultures receiving UVA/B radiation, and the formation of thymine dimers was inconspicuous. Also, UVA/B did not enhance the expression levels of DNA polymerase α or PCNA. Based on the calculation of biologically effective UV doses, daily exposure to sunlight may increase the expression of DNA polymerase α or PCNA genes in S. costatum by 12% at sea surface. This level of increase does not seriously affect the value of using these genes as growth indicators, but caution is needed in the extrapolation of this conclusion to all phytoplankton species.
PHYLOGEOGRAPHY OF GRACILARIA TIKVAHIAE (GRACILARIACEAE, RHODOPHYTA): A STUDY OF GENETIC DISCONTINUITY IN A CONTINUOUSLY DISTRIBUTED SPECIES BASED ON MOLECULAR EVIDENCE1
Authors: Gurgel Carlos Frederico Deluqui , Fredericq Suzanne , Norris James N.
Published: July 2004

Gracilaria tikvahiae, a highly morphologically variable red alga, is one of the most common species of Gracilariaceae inhabiting Atlantic estuarine environments and the Intracoastal Waterway of eastern North America. Populations of G. tikvahiae at the extremes of their geographic range (Canada and southern Mexico) are subjected to very different environmental regimes. In this study, we used two types of genetic markers, the chloroplast‐encoded rbcL and the nuclear internal transcribed spacer (ITS) region, to examine the genetic variability within G. tikvahiae, for inferring the taxonomic and phylogenetic relationships between geographically isolated populations, and to discuss its distributional information in a phylogeographic framework. Based on rbcL and ITS phylogenies, specimens from populations collected at the extreme distributional ranges reported for G. tikvahiae are indeed part of the same species; however, rbcL‐ but not ITS‐based phylogenies detected phylogenetic structure among the ten G. tikvahiae different haplotypes found in this study. The four distinct rbcL lineages were identified as 1) a Canadian–northeast U.S. lineage, 2) a southeast Florida lineage, 3) an eastern Gulf of Mexico lineage, and 4) a western Gulf of Mexico lineage. We found no evidence for the occurrence of G. tikvahiae in the Caribbean Sea. Observed phylogeographic patterns match patterns of genetic structures reported for marine animal taxa with continuous and quasicontinuous geographic distribution along the same geographic ranges.
PHYLOGENY OF AULACOSEIRA (BACILLARIOPHYTA) BASED ON MOLECULES AND MORPHOLOGY1
Authors: Edgar Stacy M. , Theriot Edward C.
Published: July 2004

The phylogeny of 67 populations representing 45 species of Aulacoseira Thwaites was estimated by maximum parsimony methods using a combination of nucleotide sequence data and qualitative and quantitative morphological characteristics of the silica cell wall gathered primarily from original observation by LM and SEM. A new type of character using continuous quantitative variables that describe the ontogenetic‐allometric trajectories of cell wall characteristics over the life cycle (size range) of diatoms is introduced. In addition to the 45 Aulacoseira species, the phylogeny also incorporated one Miosira Krammer, Lange‐Bertalot, and Schiller species and two outgroup species (Melosira varians Agardh and Stephanopyxis nipponica Gran & Yendo). Fifteen species, represented by 24 populations, also contained molecular data from the nuclear genome (18S rDNA), and 11 of these species (18 populations) contained data from the chloroplast genome (rbcL) as well, which were sequenced or downloaded from GenBank. The phylogeny of Aulacoseira is composed of five major clades: 1) an A. crenulata (Ehrenburg) Thwaites and A. italica (Ehrenburg) Simonsen clade, which is the most basal; 2) an A. granulata (Ehrenburg) Simonsen complex clade; 3) an A. ambigua (Grunow) Simonsen clade; 4) an A. subarctica (O. Müller) Haworth and A. distans (Ehrenburg) Simonsen clade; and 5) an A. islandica (O. Müller) Simonsen clade that also contained endemic species from Lake Baikal, Siberia and many extinct Aulacoseira taxa. Monophyly of Aulacoseira can only be achieved if Miosira is no longer given separate generic status.
PHYLOGENETIC ANALYSIS OF THE GENUS EUGLENA (EUGLENOPHYCEAE) WITH PARTICULAR REFERENCE TO THE TYPE SPECIES EUGLENA VIRIDIS1
Authors: Shin Woongghi , Triemer Richard E.
Published: July 2004

Euglena viridis (subgenus Euglena) serves as the type species for the genus Euglena. In this study, molecular phylogenetic analyses using a small subunit (SSU) and a combined SSU–partial large subunit rDNA data set for members of the genus Euglena showed that strains identified as E. viridis on the basis of morphology are distributed between two separate nonsister clades. Although all the E. viridis strains examined were morphologically indistinguishable and possessed spherical mucocysts and stellate chloroplasts with one paramylon center, there was a high degree of sequence divergence between the E. viridis strains in different clades, making this a cryptic species. Like E. viridis, all taxa from the subgenus Euglena are characterized by having one or more stellate chloroplasts with paramylon grains clustered around the center of the chloroplast. These additional taxa were divided into four clades in all the molecular analyses. Strains of Euglena stellata formed two nonsister clades whose members had a single aggregate chloroplast with paramylon center and spindle‐shaped mucocysts. A geniculata clade included species with one or two stellate chloroplasts with paramylon centers and spherical mucocysts, and the cantabrica clade had members with one stellate chloroplast with paramylon center and spherical mucocysts often arranged in spiral rows. Interspersed among these were three additional clades bearing taxa from the subgenus Calliglena that contains members with discoid plastids and pyrenoids that may or may not be capped with paramylon. These taxa formed a laciniata clade, mutabilis clade, and gracilis clade. This study demonstrates that E. viridis and E. stellata are cryptic species that can only be distinguished at the molecular level. Because E. viridis is the designated type species for the genus Euglena, we designated an epitype for E. viridis.
AUXOSPORE FORMATION AND THE MORPHOLOGY OF THE INITIAL CELL OF THE MARINE ARAPHID DIATOM GEPHYRIA MEDIA (BACILLARIOPHYCEAE)1
Authors: Sato Shinya , Nagumo Tamotsu , Tanaka Jiro
Published: July 2004

Recent studies have led to a rapid increase in knowledge of auxospore formation in diatoms. However, these studies have been limited to centric and raphid pennate diatoms, and there is still very little information for the araphid pennate diatoms. Using LM and SEM, we studied the development of the auxospore and the initial cell of the marine epiphytic diatom Gephyria media Arnott. Auxospores were bipolar and curved in side view, as in many other pennate diatoms. SEM revealed many transverse perizonial bands, all of which were incomplete rings. There was an elongate, sprawling, silicified structure beneath the ventral suture of the transverse perizonial bands. This structure is presumably equivalent to the longitudinal perizonial band in other pennate diatoms, although we could not determine the homologous relationship between the two features. Scales were found both in the inner wall of the perizonium and around the primary perizonial bands. The presence or absence of scales may be of phylogenetic significance in diatoms, only during the final stages of auxospore formation because scales are found in early spherical stages. The distinctive finger‐like structures observed throughout all stage of G. media have not been observed before in the other diatom taxa.
MOLECULAR IDENTIFICATION OF TWO SIBLING SPECIES UNDER THE NAME GRACILARIA CHILENSIS (RHODOPHYTA, GRACILARIALES)1,3
Authors: Cohen Séverine , Faugeron Sylvain , Martínez Enrique A. , Correa Juan A. , Viard Frédérique , Destombe Christophe , Valero Myriam
Published: July 2004

Molecular markers belonging to three different genomes, mitochondrial (cox2‐3 spacer), plastid (RUBISCO spacer), and nuclear (internal transcribed spacer 1), were used to compare Gracilaria chilensis samples collected along the Chilean coast with samples ascribed to G. chilensis from the West Pacific Ocean (New Zealand and Australia). Our data are in agreement with previous studies suggesting two sibling species currently going under the name G. chilensis that co‐occur in New Zealand. One of these, a New Zealand sample previously examined by Bird and others in 1990, is conspecific with G. chilensis from Chile. Finally, our results demonstrate clearly that most of the sequences in GenBank reported as G. chilensis are based on misidentified material.
EFFECTS OF ISLAND GROUPS, DEPTH, AND EXPOSURE TO OCEAN WAVES ON SUBTIDAL MACROALGAL ASSEMBLAGES IN THE RECHERCHE ARCHIPELAGO, WESTERN AUSTRALIA1
Authors: Goldberg Nisse A. , Kendrick Gary A.
Published: July 2004

Temperate Australia has a speciose highly endemic algal flora. This study explored the influence of geographical isolation between islands, depth and exposure to ocean swells on the diversity of macroalgae in the Recherche Archipelago (Western Australia). Macroalgae were harvested (0.25‐m2 quadrats) from sites at two exposures (sheltered and exposed to wave energy), three depths (<10, 10–20, and 21–28 m), and two island groups (three islands within Esperance Bay and three islands outside the bay). A total of 220 species were collected. Species richness and biomass were significantly different at the smallest spatial scale (0.25 m2), and density of overstory species decreased with depth. Results from analysis of similarity tests suggested that macroalgal assemblages differed with depth, exposure and to a lesser extent with island group. Assemblage differences were often associated with particular overstory or understory taxa and not the entire assemblage composition. Average species richness·0.25 m−2 ranged from 13 to 29 species, typically with a few species contributing more than 50% of average biomass. Species richness was maintained by species turnover at the 0.25‐m2 spatial scale. Our results suggest that richness in temperate Australia is maintained by turnover of broadly distributed species. More dominant species in assemblages were associated with differences in depth and exposure to ocean swells. Our findings support the hypothesis of a geographical transition of dominant species from kelp‐dominated in the west to a fucalean‐dominated assemblage in the Recherche Archipelago and east of the Great Australian Bight.
GROWTH AND DOMOIC ACID PRODUCTION BY PSEUDO‐NITZSCHIA SERIATA (BACILLARIOPHYCEAE) UNDER PHOSPHATE AND SILICATE LIMITATION1
Authors: Fehling Johanna , Davidson Keith , Bolch Christopher J. , Bates Stephen S.
Published: July 2004

Pseudo‐nitzschia seriata (Cleve) H. Peragallo isolated from Scottish west coast waters was studied in batch culture with phosphate (P) or silicate (Si) as the yield‐limiting nutrient at 15°C. This species produced the neurotoxin domoic acid (DA) when either nutrient was limiting but produced more when stressed by Si limitation during the stationary phase. Under P‐limiting conditions, exponential growth stopped after P was reduced to a low threshold concentration. Under Si‐limiting conditions, fast exponential growth was followed by a period of slower exponential growth, until Si became exhausted. A stationary phase was observed in the P‐limited but not the Si‐limited cultures, the latter showing a rapid decrease in cell density after the second exponential growth phase. Si‐limited cultures exhibited a further period of active metabolism (as indicated by increases in chl and carbon per cell) late in the experiment, presumably fueled by regenerated Si. DA production was low in exponential phase under both conditions. In P‐limited cultures, most DA was produced during the immediate postexponential phase, with little or no new DA produced during later cell senescence. In contrast, although a substantial amount of DA was produced during the slower exponential phase of the Si‐limited cultures, DA production was even greater near the end of the experiment, coincident with the period of chl synthesis and increase in carbon biomass. Comparison of the magnitude of toxin production in the two nutrient regimes indicated a greater threat of P. seriata‐generated amnesic shellfish poisoning events under Si rather than P nutrient limitation.
PHOTOSYNTHESIS AND COLD ACCLIMATION: MOLECULAR EVIDENCE FROM A POLAR DIATOM1
Authors: Mock Thomas , Valentin Klaus
Published: July 2004

The psychrophilic diatomFragilariopsis cylindrus(Grunow) Krieger in Helmcke & Krieger was used to investigate photosynthesis and growth under freezing temperatures. Gene expression during a temperature shift from +5° C to −1.8° C was studied under 3 and 35 μmol photons·m−2·s−1by using a macroarray. These measurements were paralleled by determination of fluorescence induction at PSII and pigment analysis. The shift to −1.8° C at 35 μmol photons·m−2·s−1caused a marginal decrease of photosynthetic quantum yield (Fv/Fm) from 0.61 to 0.52 with fast recovery after 1 day. The ratio of chlcto chlaincreased from 3.1 to 5.5, and the ratio of diatoxanthin to diadinoxanthin increased from 0.7 to 5.0. Genes encoding proteins of PSII (psbA, psbC) and for carbon fixation (rbcL) were down‐regulated, whereas genes encoding chaperons (hsp70) and genes for plastid protein synthesis and turnover (elongation factorEfTs, ribosomal proteinrpS4,ftsHprotease) were up‐regulated. In contrast, cold exposure at 3 μmol photons·m−2·s−1induced a marginal increase in Fv/Fmfrom 0.61 to 0.63 and a strong increase in fucoxanthin concentrations from 0.04 up to 0.12 pg·cell−1. This was paralleled by up‐regulation offcpgenes. The ratio of chlcto chlaalso increased from 3.1 to 4.2, as did the ratio of diatoxanthin to diadinoxanthin from 0.7 to 2.2. Down‐regulation ofpsbA,psbC, andrbcL could also be measured but not up‐regulation ofhsp70,EfTs,rpS4, and theftsHprotease. The latter genes are probably necessary to avoid cold shock photoinhibition only at higher light intensities.
Demonstration of a second rapidly conducting cortico‐diaphragmatic pathway in humans
Authors: Sharshar Tarek , Hopkinson Nicholas S , Jonville Sophie , Prigent Hélène , Carlier Robert , Dayer Mark J. , Swallow Elisabeth B , Lofaso Frédéric , Moxham John , Polkey Michael I.
Published: July 2004

Functional imaging studies in normal humans have shown that the supplementary motor area (SMA) and the primary motor cortex (PMC) are coactivated during various breathing tasks. It is not known whether a direct pathway from the SMA to the diaphragm exists, and if so what properties it has. Using transcranial magnetic stimulation (TMS) a site at the vertex, representing the diaphragm primary motor cortex, has been identified. TMS mapping revealed a second area 3 cm anterior to the vertex overlying the SMA, which had a rapidly conducting pathway to the diaphragm (mean latency 16.7 ± 2.4 ms). In comparison to the vertex, the anterior position was characterized by a higher diaphragm motor threshold, a greater proportional increase in motor‐evoked potential (MEP) amplitude with voluntary facilitation and a shorter silent period. Stimulus–response curves did not differ significantly between the vertex and anterior positions. Using paired TMS, we also compared intracortical inhibition/facilitation (ICI/ICF) curves. In comparison to the vertex, the MEP elicited from the anterior position was not inhibited at short interstimulus intervals (1–5 ms) and was more facilitated at long interstimulus intervals (9–20 ms). The patterns of response were identical for the costal and crural diaphragms. We conclude that the two coil positions represent discrete areas that are likely to be the PMC and SMA, with the latter wielding a more excitatory effect on the diaphragm.
Nicotine increases initial blood flow responses to local heating of human non‐glabrous skin
Authors: Warner David O. , Joyner Michael J. , Charkoudian Nisha
Published: July 2004

Nicotine affects the regulation of skin blood flow (SkBF), but the mechanisms involved are not well understood. We tested the hypothesis that acute exposure to nicotine inhibits both the initial neurally mediated component and the later sustained component of SkBF responses to local heating of non‐glabrous skin in humans. SkBF (measured by laser‐Doppler) responses to local heating of forearm skin from 32 to 42°C were measured in 11 chronic smokers. Heating occurred at one site over 15 min (RAMP) and over 90 s (STEP) at another site, and was maintained for an additional 30 min. STEP heating was also applied to a site pretreated with bretylium via iontophoresis to inhibit noradrenergic neurotransmission. Responses were measured before and after acute administration of nicotine via cigarettes or nasal spray in two experimental sessions. Nicotine decreased resting skin blood flow (P < 0.05); this response was inhibited by bretylium. During RAMP, nicotine increased the initial SkBF at 42°C (by ∼12%, P < 0.05). For STEP, nicotine increased the initial peak response (by ∼25%, P < 0.05), and decreased the sustained plateau value (by ∼10%, P < 0.05). In skin pretreated with bretylium, the increase caused by nicotine in the initial peak value persisted, but the plateau value was not different from pre‐nicotine. These data suggest that in abstinent cigarette smokers, nicotine augments initial responses to both gradual and rapid non‐painful heating of non‐glabrous skin by sensitizing the sensory nerves that mediate the axon reflex associated with rapid vasodilatation. In contrast, nicotine decreases SkBF responses to prolonged heating by activating noradrenergic nerves.
Functional properties of K+ currents in adult mouse ventricular myocytes
Authors: Brouillette Judith , Clark Robert B. , Giles Wayne R. , Fiset Céline
Published: July 2004

Although the K+ currents expressed in hearts of adult mice have been studied extensively, detailed information concerning their relative sizes and biophysical properties in ventricle and atrium is lacking. Here we describe and validate pharmacological and biophysical methods that can be used to isolate the three main time‐ and voltage‐dependent outward K+ currents which modulate action potential repolarization. A Ca2+‐independent transient outward K+ current, Ito, can be separated from total outward current using an ‘inactivating prepulse’. The rapidly activating, slowly inactivating delayed rectifier K+ current, IKur, can be isolated using submillimolar concentrations of 4‐aminopyridine (4‐AP). The remaining K+ current, Iss, can be obtained by combining these two procedures: (i) inactivating Ito and (ii) eliminating IKur by application of low concentration of 4‐AP. Iss activates relatively slowly and shows very little inactivation, even during depolarizations lasting several seconds. Our findings also show that the rate of reactivation of Ito is more than 20‐fold faster than that of IKur. These results demonstrate that the outward K+ currents in mouse ventricles can be separated based on their distinct time and voltage dependence, and different sensitivities to 4‐AP. Data obtained at both 22 and 32°C demonstrate that although the duration of the inactivating prepulse has to be adapted for the recording temperature, this approach for separation of K+ current components is also valid at more physiological temperatures. To demonstrate that these methods also allow separation of these K+ currents in other cell types, we have applied this same approach to myocytes from mouse atria. Molecular approaches have been used to compare the expression levels of different K+ channels in mouse atrium and ventricle. These findings provide new insights into the functional roles of IKur, Ito and Iss during action potential repolarization.
Ghrelin stimulates neurogenesis in the dorsal motor nucleus of the vagus
Authors: Zhang Weizhen , Lin Theodore R. , Hu Yuexuan , Fan Yongyi , Zhao Lili , Stuenkel Edward L. , Mulholland Michael W.
Published: July 2004

Ghrelin, a gastric peptide hormone, has been reported to regulate growth hormone secretion and energy homeostasis. Here we show that ghrelin promotes neural proliferation in vivo and in vitro in the rat dorsal motor nucleus of the vagus (DMNV). Ghrelin receptor mRNA and immunoreactivity were detected in tissues from DMNV. Systemic administration of ghrelin (130 nmol kg−1) significantly increased 5‐bromo‐2′‐deoxyuridine (BrdU) incorporation in the DMNV in adult rats with cervical vagotomy (BrdU positive cells; from 27 ± 4 to 69 ± 14 n= 5, P < 0.05). In vitro, exposure of cultured DMNV neurones to ghrelin significantly increased the percentage of BrdU incorporation into cells in both dose‐dependent (10−9–10−6m), and time‐dependent (6 h to 48 h) manners. Ghrelin significantly increased voltage‐activated calcium currents in isolated single DMNV neurones from a mean maximal change of 141 ± 26 pA to 227 ± 37 pA. Upon removal of ghrelin, calcium currents slowly returned to baseline. Blocking L‐type calcium channels by diltiazem (10 μm) significantly attenuated ghrelin‐mediated increments in BrdU incorporation (n= 5, P < 0.05). Ghrelin acts directly on DMNV neurones to stimulate neurogenesis.
State‐dependent trapping of flecainide in the cardiac sodium channel
Authors: Ramos Eugene , O'Leary Michael E.
Published: July 2004

Flecainide is a Class I antiarrhythmic drug and a potent inhibitor of the cardiac (Nav1.5) sodium channel. Although the flecainide inhibition of Nav1.5 is typically enhanced by depolarization, the contributions of the open and inactivated states to flecainide binding and inhibition remain controversial. We further investigated the state‐dependent binding of flecainide by examining its inhibition of rapidly inactivating and non‐inactivating mutants of Nav1.5 expressed in Xenopus oocytes. Applying flecainide while briefly depolarizing from a relatively negative holding potential resulted in a low‐affinity inhibition of the channel (IC50= 345 μm). Increasing the frequency of stimulation potentiated the flecainide inhibition (IC50= 7.4 μm), which progressively increased over the range of voltages where Nav1.5 channels activated. This contrasts with sustained depolarizations that effectively stabilize the channels in inactivated states, which failed to promote significant flecainide inhibition. The voltage sensitivity and strong dependence of the flecainide inhibition on repetitive depolarization suggests that flecainide binding is facilitated by channel opening and that the drug does not directly bind to closed or inactivated channels. The binding of flecainide to open channels was further investigated in a non‐inactivating mutant of Nav1.5. Flecainide produced a time‐dependent decay in the current of the non‐inactivating mutant that displayed kinetics consistent with a simple pore blocking mechanism (KD= 11 μm). At hyperpolarized voltages, flecainide slowed the recovery of both the rapidly inactivating (τ= 81 ± 3 s) and non‐inactivating (τ= 42 ± 3 s) channels. Mutation of a conserved isoleucine of the D4S6 segment (I1756C) creates an alternative pathway that permits the rapid diffusion of anaesthetics out of the Nav1.5 channel. The I1756C mutation accelerated the recovery of both the rapidly inactivating (τ= 12.6 ± 0.4 s) and non‐inactivating (τ= 7.4 ± 0.1 s) channels, suggesting that flecainide is trapped and not tightly bound within the pore when the channels are closed or inactivated. The data indicate that flecainide rapidly gains access to its binding site when the channel is open and inhibits Na+ current by a pore blocking mechanism. Closing of either the activation or the inactivation gate traps flecainide within the pore resulting in the slow recovery of the drug‐modified channels at hyperpolarized voltages.
Neurotransmitter modulation of extracellular H+ fluxes from isolated retinal horizontal cells of the skate
Authors: Molina Anthony J. A. , Verzi Michael P. , Birnbaum Andrea D. , Yamoah Ebenezer N. , Hammar Katherine , Smith Peter J. S. , Malchow Robert Paul
Published: July 2004

Self‐referencing H+‐selective microelectrodes were used to measure extracellular H+ fluxes from horizontal cells isolated from the skate retina. A standing H+ flux was detected from quiescent cells, indicating a higher concentration of free hydrogen ions near the extracellular surface of the cell as compared to the surrounding solution. The standing H+ flux was reduced by removal of extracellular sodium or application of 5‐(N‐ethyl‐N‐isopropyl) amiloride (EIPA), suggesting activity of a Na+–H+ exchanger. Glutamate decreased H+ flux, lowering the concentration of free hydrogen ions around the cell. AMPA/kainate receptor agonists mimicked the response, and the AMPA/kainate receptor antagonist 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione (CNQX) eliminated the effects of glutamate and kainate. Metabotropic glutamate agonists were without effect. Glutamate‐induced alterations in H+ flux required extracellular calcium, and were abolished when cells were bathed in an alkaline Ringer solution. Increasing intracellular calcium by photolysis of the caged calcium compound NP‐EGTA also altered extracellular H+ flux. Immunocytochemical localization of the plasmalemma Ca2+–H+‐ATPase (PMCA pump) revealed intense labelling within the outer plexiform layer and on isolated horizontal cells. Our results suggest that glutamate modulation of H+ flux arises from calcium entry into cells with subsequent activation of the plasmalemma Ca2+–H+‐ATPase. These neurotransmitter‐induced changes in extracellular pH have the potential to play a modulatory role in synaptic processing in the outer retina. However, our findings argue against the hypothesis that hydrogen ions released by horizontal cells normally act as the inhibitory feedback neurotransmitter onto photoreceptor synaptic terminals to create the surround portion of the centre‐surround receptive fields of retinal neurones.
Persistent decrease in synaptic efficacy induced by nicotine at Schaffer collateral–CA1 synapses in the immature rat hippocampus
Authors: Maggi Laura , Sola Elisabetta , Minneci Federico , Le Magueresse Corentin , Changeux Jean Pierre , Cherubini Enrico
Published: July 2004

Neuronal nicotinic acetylcholine receptors (nAChRs) are widely distributed within the brain where they contribute to the regulation of higher cognitive functions. The loss of the cholinergic function in Alzheimer's disease patients, along with the well‐known memory enhancing effect of nicotine, emphasizes the role of cholinergic signalling in memory functions. The hippocampus, a key structure in learning and memory, is endowed with nAChRs localized at pre‐ and postsynaptic levels. In previous work on the immature hippocampus we have shown that, at low probability (P) synapses, activation of α7 nAChRs by nicotine or by endogenously released acetylcholine persistently enhanced glutamate release and converted ‘presynaptically silent’ synapses into functional ones. Here we show that in the same preparation, at high P synapses, nicotine induces long‐term depression of AMPA‐ and NMDA‐mediated synaptic currents. This effect was mediated by presynaptic α7‐ and β2‐containing receptors and was associated with an increase in the paired pulse ratio and in the coefficient of variation. High P synapses could be converted into low P and vice versa by changing the extracellular Ca2+/Mg2+ ratio. In these conditions nicotine was able to persistently potentiate or depress synaptic responses depending on the initial P‐values. A bi‐directional control of synaptic plasticity by nicotine would considerably enhance the computational properties of the network during a critical period of postnatal development thus contributing to sculpt the neuronal circuit.
Cannabinoids suppress synaptic input to neurones of the rat dorsal motor nucleus of the vagus nerve
Authors: Derbenev Andrei V. , Stuart Thomas C. , Smith Bret N.
Published: July 2004

Cannabinoids bind central type 1 receptors (CB1R) and modify autonomic functions, including feeding and anti‐emetic behaviours, when administered peripherally or into the dorsal vagal complex. Western blots and immunohistochemistry indicated the expression of CB1R in the rat dorsal vagal complex, and tissue polymerase chain reaction confirmed that CB1R message was made within the region. To identify a cellular substrate for the central autonomic effects of cannabinoids, whole‐cell patch‐clamp recordings were made in brainstem slices to determine the effects of CB1R activation on synaptic transmission to neurones of the dorsal motor nucleus of the vagus (DMV). A subset of these neurones was identified as gastric related after being labelled retrogradely from the stomach. The CB1R agonists WIN55,212‐2 and anandamide decreased the frequency of spontaneous excitatory or inhibitory postsynaptic currents in a concentration‐related fashion, an effect that persisted in the presence of tetrodotoxin. Paired pulse ratios of electrically evoked postsynaptic currents were also increased by WIN55,212‐2. The effects of  WIN55,212‐2 were sensitive to the selective CB1R antagonist AM251. Cannabinoid agonist effects on synaptic input originating from neurones in the nucleus tractus solitarius (NTS) were determined by evoking activity in the NTS with local glutamate application. Excitatory and inhibitory synaptic inputs arising from the NTS were attenuated by WIN55,212‐2. Our results indicate that cannabinoids inhibit transfer of synaptic information to the DMV, including that arising from the NTS, in part by acting at receptors located on presynaptic terminals contacting DMV neurones. Inhibition of synaptic input to DMV neurones is likely to contribute to the suppression of visceral motor responses by cannabinoids.
An estimate of the resting membrane resistance of frog olfactory receptor neurones
Authors: Pun Raymund Y. K. , Kleene Steven J.
Published: July 2004

The ability of a frog olfactory receptor neurone (ORN) to respond to odorous molecules depends on its resting membrane properties, including membrane resistance and potential. Quantification of these properties is difficult because of a shunt conductance at the membrane–pipette seal that is in parallel with the true membrane conductance. In physiological salines, the sum of these two conductances averaged 235 pS. We used ionic substitution and channel blockers to reduce the membrane conductance as much as possible. This yielded a lower limit for the membrane conductance of 158 pS. The upper limit of resting membrane resistance, then, is 6 GΩ. The membrane is permeable to K+ and, to a lesser extent, other cations. No resting Cl− conductance was detectable. Correcting measured zero‐current potentials for distortion by the shunt suggests that the resting membrane potential is no more negative than −75 mV. The present results help to explain why frog ORNs are excitable at rest.