Effects of manganese-excess on CO<Subscript>2</Subscript> assimilation,ribulose-1,5-bisphosphate carboxylase/oxygenase,carbohydrates and photosynthetic electron transport of leaves,and antioxidant systems of leaves and roots in <Emphasis Type="Italic">Citrus grandis</Emphasis>seedlings

Background  

Very little is known about the effects of manganese (Mn)-excess on citrus photosynthesis and antioxidant systems. Seedlings of sour pummelo (Citrus grandis) were irrigated for 17 weeks with nutrient solution containing 2 μM (control) or 500 μM (excess) MnSO₄. The objective of this study were to understand the mechanisms by which Mn-excess leads to a decrease in CO₂ assimilation and to test the hypothesis that Mn-induced changes in antioxidant systems differ between roots and leaves.     

Assessing the in vitro toxicity of the lunar dust environment using respiratory cells exposed to Al<Subscript>2</Subscript>O<Subscript>3</Subscript> or SiO<Subscript>2</Subscript> fine dust particles

Prior chemical and physical analysis of lunar soil suggests a composition of dust particles that may contribute to the development of acute and chronic respiratory disorders. In this study, fine Al₂O₃ (0.7 μm) and fine SiO₂ (mean 1.6 μm) were used to assess the cellular uptake and cellular toxicity of lunar dust particle analogs. Respiratory cells, murine alveolar macrophages (RAW 264.7) and human type II epithelial (A549), were cultured as the in vitro model system. The phagocytic activity of both cell types using ultrafine (0.1 μm) and fine (0.5 μm) fluorescent polystyrene beads was determined. Following a 6-h exposure, RAW 264.7 cells had extended pseudopods with beads localized in the cytoplasmic region of cells. After 24 h, the macrophage cells were rounded and clumped and lacked pseudopods, which suggest impairment of phagocytosis. A549 cells did not contain beads, and after 24 h, the majority of the beads appeared to primarily coat the surface of the cells. Next, we investigated the cellular response to fine SiO₂ and Al₂O₃ (up to 5 mg/ml). RAW 264.7 cells exposed to 1.0 mg/ml of fine SiO₂ for 6 h demonstrated pseudopods, cellular damage, apoptosis, and necrosis. A549 cells showed slight toxicity when exposed to fine SiO₂ for the same time and dose. A549 cells had particles clustered on the surface of the cells. Only a higher dose (5.0 mg/ml) of fine SiO₂ resulted in a significant cytotoxicity to A549 cells. Most importantly, both cell types showed minimal cytotoxicity following exposure to fine Al₂O₃. Overall, this study suggests differential cellular toxicity associated with exposure to fine mineral dust particles.     

Sucrose monolaurate synthesis with Protex 6L immobilized on electrospun TiO<Subscript>2</Subscript> nanofiber

TiO₂ nanofibers with uniform diameter about 125 nm were prepared based on sol–gel process and electrospinning technology. Protex 6L, an industrial alkaline protease, was covalently immobilized on TiO₂ nanofiber through γ-aminopropyltriethoxysilane modification and glutaraldehyde crosslinking. With 2 (v/v)% glutaraldehyde as crosslinker, the enzyme loading is about 201 mg (g nanofiber membrane)⁻¹, and the specific activity of the immobilized Protex 6L is 2.45 μmol h⁻¹ ml⁻¹ mg⁻¹ protein for synthesis of sucrose monolaurate from sucrose and vinyl laurate. The optimal condition for sucrose monolaurate production is 5% (v/v) water content in DMSO/2-methyl-2-butanol solvent mixture and 50°C. Under this condition, 97% conversion was achieved within 36 h by nanofibrous Protex 6L, which is corresponding to a productivity 34 times higher than that of most widely used Novozym 435. After 10 cycles reuse, nanofibrous Protex 6L retained 52.4% of its original activity.     

Interaction Between Nanoparticulate Anatase TiO<Subscript>2</Subscript> and Lactate Dehydrogenase

In order to study the mechanisms underlying the effects of TiO₂ nanoparticles on lactate dehydrogenase (LDH, EC1.1.1.27), Institute of Cancer Research region mice were injected with nanoparticulate anatase TiO₂ (5 nm) of various doses into the abdominal cavity daily for 14 days. We then examined LDH activity in vivo and in vitro and direct evident for interaction between nanoparticulate anatase TiO₂ and LDH using spectral methods. The results showed that nanoparticulate anatase TiO₂ could significantly activate LDH in vivo and in vitro; the kinetics constant (Km) and Vmax were 0.006 μM and 1,149 unit mg⁻¹ protein min⁻¹, respectively, at a low concentration of nanoparticulate anatase TiO₂, and 3.45 and 0.031 μM and 221 unit mg⁻¹ protein min⁻¹, respectively, at a high concentration of nanoparticulate anatase TiO₂. By fluorescence spectral assays, the nanoparticulate anatase TiO₂ was determined to be directly bound to LDH, and the binding constants of the binding site were 1.77 × 10⁸ L mol⁻¹ and 2.15 × 10⁷ L mol⁻¹, respectively, and the binding distance between nanoparticulate anatase TiO₂ and the Trp residue of LDH was 4.18 nm, and nanoparticulate anatase TiO₂ induced the protein unfolding. It was concluded that the binding of nanoparticulate anatase TiO₂ altered LDH structure and function.     

Effects of temperature,photosynthetic photon flux density,photoperiod and O<Subscript>2</Subscript> and CO<Subscript>2</Subscript> concentrations on growth rates of the symbiotic dinoflagellate, <Emphasis Type="Italic">Amphidinium</Emphasis> sp.

Symbiotic dinoflagellates of the species Amphidinium are expected to be pharmaceutically useful microalgae because they produce antitumor macrolides. A microalgae production system with a large number of cells at a high density has been developed for the efficient production of macrolide compounds. In the present study, the effects of culture conditions on the cellular growth rate of dinoflagellates were investigated to determine the optimum culture conditions for obtaining high yields of microalgae. Amphidinium species was cultured under conditions with six temperature levels (21–35°C), six levels of photosynthetic photon flux density (15–70 μmol photons m⁻² s⁻¹), three levels of CO₂ concentration (0.02–0.1%), and three levels of O₂ concentration (0.2–21%). The number of cells cultured in a certain volume of solution was monitored microscopically and the cellular growth rate was expressed as the specific growth rate. The maximum specific growth rate was 0.022 h⁻¹ at a temperature of 26°C and O₂ concentration of 5%, and the specific growth rate was saturated at a CO₂ concentration of 0.05%, a photosynthetic photon flux density of 35 μmol photons m⁻² s⁻¹ and a photoperiod of 12 h day⁻¹ upon increasing each environmental parameter. The results demonstrate that Amphidinium species can multiply efficiently under conditions of relatively low light intensity and low O₂ concentration.     

Soil-Atmosphere Exchange of N<Subscript>2</Subscript>O and NO in Near-Natural Savanna and Agricultural Land in Burkina Faso (W. Africa)

In a combined field and laboratory study in the southwest of Burkina Faso, we quantified soil-atmosphere N₂O and NO exchange. N₂O emissions were measured during two field campaigns throughout the growing seasons 2005 and 2006 at five different experimental sites, that is, a natural savanna site and four agricultural sites planted with sorghum (n = 2), cotton and peanut. The agricultural fields were not irrigated and not fertilized. Although N₂O exchange mostly fluctuated between −2 and 8 μg N₂O–N m⁻² h⁻¹, peak N₂O emissions of 10–35 μg N₂O–N m⁻² h⁻¹ during the second half of June 2005, and up to 150 μg N₂O–N m⁻² h⁻¹ at the onset of the rainy season 2006, were observed at the native savanna site, whereas the effect of the first rain event on N₂O emissions at the crop sites was low or even not detectable. Additionally, a fertilizer experiment was conducted at a sorghum field that was divided into three plots receiving different amounts of N fertilizer (plot A: 140 kg N ha⁻¹; plot B: 52.5 kg N ha⁻¹; plot C: control). During the first 3 weeks after fertilization, only a minor increase in N₂O emissions at the two fertilized plots was detected. After 24 days, however, N₂O emission rates increased exponentially at plot A up to a mean of 80 μg N₂O–N m⁻² h⁻¹, whereas daily mean values at plot B reached only 19 μg N₂O–N m⁻² h⁻¹, whereas N₂O flux rates at plot C remained unchanged. The calculated annual N₂O emission of the nature reserve site amounted to 0.52 kg N₂O–N ha⁻¹ a⁻¹ in 2005 and to 0.67 kg N₂O–N ha⁻¹ a⁻¹ in 2006, whereas the calculated average annual N₂O release of the crop sites was only 0.19 kg N₂O–N ha⁻¹ a⁻¹ and 0.20 kg N₂O–N ha⁻¹ a⁻¹ in 2005 and 2006, respectively. In a laboratory study, potential N₂O and NO formation under different soil moisture regimes were determined. Single wetting of dry soil to medium soil water content with subsequent drying caused the highest increase in N₂O and NO emissions with maximum fluxes occurring 1 day after wetting. The stimulating effect lasted for 3–4 days. A weaker stimulation of N₂O and NO fluxes was detected during daily wetting of soil to medium water content, whereas no significant stimulating effect of single or daily wetting to high soil water content (>67% WHC_max) was observed. This study demonstrates that the impact of land-use change in West African savanna on N trace gas emissions is smaller—with the caveat that there could have been potentially higher N₂O and NO emissions during the initial conversion—than the effect of timing and distribution of rainfall and of the likely increase in nitrogen fertilization in the future.     

Effect of 24-Epibrassinolide on Chlorophyll Fluorescence and Photosynthetic CO<Subscript>2</Subscript> Assimilation in <Emphasis Type="Italic">Vicia faba</Emphasis> Plants Treated with the Photosynthesis-Inhibiting Herbicide Terbutryn

Simultaneous measurements of chlorophyll (Chl) fluorescence and CO₂ assimilation (A) in Vicia faba leaves were taken during the first weeks of growth to evaluate the protective effect of 24-epibrassinolide (EBR) against damage caused by the application of the herbicide terbutryn (Terb) at pre-emergence. V. faba seeds were incubated for 24 h in EBR solutions (2 × 10⁻⁶ or 2 × 10⁻⁵ mM) and immediately sown. Terb was applied at recommended doses (1.47 or 1.96 kg ha⁻¹) at pre-emergence. The highest dose of Terb strongly decreased CO₂ assimilation, the maximum quantum yield of PSII photochemistry in the dark-adapted state (F _V/F _M), the nonphotochemical quenching (NPQ), and the effective quantum yield (ΔF/F′_M) during the first 3–4 weeks after plant emergence. Moreover, Terb increased the basal quantum yield of nonphotochemical processes (F ₀/F _M)_, the degree of reaction center closure (1 − q _p), and the fraction of light absorbed in PSII antennae that was dissipated via thermal energy dissipation in the antennae (1 − F′_V/F′_M). The herbicide also significantly reduced plant growth at the end of the experiment as well as plant length, dry weight, and number of leaves. The application of EBR to V. faba seeds before sowing strongly diminished the effect of Terb on fluorescence parameters and CO₂ assimilation, which recovered 13 days after plant emergence and showed values similar to those of control plants. The protective effect of EBR on CO₂ assimilation was detected at a photosynthetic photon flux density (PFD) of 650 μmol m⁻² s⁻¹ and the effect on ΔF/F′_M and photosynthetic electron transport (J) was detected under actinic lightings up to 1750 μmol m⁻² s⁻¹. The highest dose of EBR also counteracted the decrease in plant growth caused by Terb, and plants registered the same growth values as controls.     

The control of mitochondrial succinate-dependent H<Subscript>2</Subscript>O<Subscript>2</Subscript> production

In brain mitochondria succinate activates H₂O₂ release, concentration dependently (starting at 15 μM), and in the presence of NAD dependent substrates (glutamate, pyruvate, β-hydroxybutyrate). We report that TCA cycle metabolites (citrate, isocitrate, α-ketoglutarate, fumarate, malate) individually and quickly inhibit H₂O₂ release. When they are present together at physiological concentration (0.2, 0.01, 0.15, 0.12, 0.2 mM respectively) they decrease H₂O₂ production by over 60% at 0.1–0.2 mM succinate. The degree of inhibition depends on the concentration of each metabolite. Acetoacetate is a strong inhibitor of H₂O₂ release, starting at 10 μM and acting quickly. It potentiates the inhibition induced by TCA cycle metabolites. The action of acetoacetate is partially removed by β-hydroxybutyrate. Removal is minimal at 0.1 mM acetoacetate, and is higher at 0.5 mM acetoacetate. We conclude that several inhibitors of H₂O₂ release act jointly and concentration dependently to rapidly set the required level of H₂O₂ generation at each succinate concentration.     

Changes in growth and photosynthetic patterns of oil palm (<Emphasis Type="Italic">Elaeis guineensis</Emphasis> Jacq.) seedlings exposed to short-term CO<Subscript>2</Subscript> enrichment in a closed top chamber

Three varieties of oil palm seedlings (Deli Yangambi, Deli Urt, Deli AVROS) were exposed to three levels of CO₂ (400, 800, 1,200 μmol/mol) in split plot design to determine growth (net assimilation rate, NAR; relative growth rate, RGR) and photosynthetic patterns of the seedlings under short-term CO₂ exposure of 15 weeks. Increasing CO₂ from 400 to 800 and 1,200 μmol/mol significantly enhanced total biomass and leaf area, net photosynthesis (A) and water use efficiency (WUE) especially from weeks 9 to 15. By the end of week 15, total biomass increased by 113%, and A and WUE by one- and fivefold, respectively, while specific leaf area decreased by 37%. Both enhanced biomass and A under elevated CO₂ were effective in modifying NAR and RGR as shown by high correlation coefficient values (r ² = 0.68 and 0.72; r ² = 0.63 and 0.67, respectively), although WUE seemed to have more influence over the NAR (r ² = 0.97) and RGR (r ² = 0.93). Neither interspecific preference nor its interaction with CO₂ imposed any significant effect on parameters observed. Growth improvement with CO₂ seemed able to produce healthy, bigger and vigorous oil palm seedlings, and the technique may have potential to be developed for use to reduce nursery period.     

Recent improvements in the development of A<Subscript>2B</Subscript> adenosine receptor agonists

Adenosine is known to exert most of its physiological functions by acting as local modulator at four receptor subtypes named A₁, A_2A, A_2B and A₃ (ARs). Principally as a result of the difficulty in identifying potent and selective agonists, the A_2B AR is the least extensively characterised of the adenosine receptors family. Despite these limitations, growing understanding of the physiological meaning of this target indicates promising therapeutic perspectives for specific ligands. As A_2B AR signalling seems to be associated with pre/postconditioning cardioprotective and anti-inflammatory mechanisms, selective agonists may represent a new therapeutic group for patients suffering from coronary artery disease. Herein we present an overview of the recent advancements in identifying potent and selective A_2B AR agonists reported in scientific and patent literature. These compounds can be classified into adenosine-like and nonadenosine ligands. Nucleoside-based agonists are the result of modifying adenosine by substitution at the N ⁶-, C²-positions of the purine heterocycle and/or at the 5′-position of the ribose moiety or combinations of these substitutions. Compounds 1-deoxy-1-{6-[N′-(furan-2-carbonyl)-hydrazino]-9H-purin-9-yl}-N-ethyl-β-D-ribofuranuronamide (19, hA₁ K _i = 1050 nM, hA_2A K _i = 1550 nM, hA_2B EC₅₀ = 82 nM, hA₃ K _i > 5 μM) and its 2-chloro analogue 23 (hA₁ K _i = 3500 nM, hA_2A K _i = 4950 nM, hA_2B EC₅₀ = 210 nM, hA₃ K _i > 5 μM) were confirmed to be potent and selective full agonists in a cyclic adenosine monophosphate (cAMP) functional assay in Chinese hamster ovary (CHO) cells expressing hA_2B AR. Nonribose ligands are represented by conveniently substituted dicarbonitrilepyridines, among which 2-[6-amino-3,5-dicyano-4-[4-(cyclopropylmethoxy)phenyl]pyridin-2-ylsulfanyl]acetamide (BAY-60–6583, hA₁, hA_2A, hA₃ EC₅₀ > 10 μM; hA_2B EC₅₀ = 3 nM) is currently under preclinical-phase investigation for treating coronary artery disorders and atherosclerosis.     

Ivermectin-dependent release of IL-1beta in response to ATP by peritoneal macrophages from P2X<Subscript>7</Subscript>-KO mice

The response to ATP of peritoneal macrophages from wild-type (WT) and P2X₇-invalidated (KO) mice was tested. Low concentrations (1–100 μM) of ATP transiently increased the intracellular concentration of calcium ([Ca²⁺]_i) in cells from both mice. The inhibition of the polyphosphoinositide-specific phospholipase C with U73122 inhibited this response especially in WT mice suggesting that the responses coupled to P2Y receptors were potentiated by the expression of P2X₇ receptors. One millimolar ATP provoked a sustained increase in the [Ca²⁺]_i only in WT mice. The response to 10 μM ATP was potentiated and prolonged by ivermectin in both mice. One millimolar ATP increased the influx of extracellular calcium, decreased the intracellular concentration of potassium ([K⁺]_i) and stimulated the secretion of interleukin-1β (IL-1β) only in cells from WT mice. Ten micromolar ATP in combination with 3 μM ivermectin reproduced these responses both in WT and KO mice. The secretion of IL-1β was also increased by nigericin in WT mice and the secretory effect of a combination of ivermectin with ATP in KO mice was suppressed in a medium containing a high concentration of potassium. In WT mice, 150 μM BzATP stimulated the uptake of YOPRO-1. Incubation of macrophages from WT and KO mice with 10 μM ATP resulted in a small increase of YOPRO-1 uptake, which was potentiated by addition of 3 μM ivermectin. The uptake of this dye was unaffected by pannexin-1 blockers. In conclusion, prolonged stimulation of P2X₄ receptors by a combination of low concentrations of ATP plus ivermectin produced a sustained activation of the non-selective cation channel coupled to this receptor. The ensuing variations of the [K⁺]_i triggered the secretion of IL-1β. Pore formation was also triggered by activation of P2X₄ receptors. Higher concentrations of ATP elicited similar responses after binding to P2X₇ receptors. The expression of the P2X₇ receptors was also coupled to a better response to P2Y receptors.     

CO<Subscript>2</Subscript>-enriched microenvironment affects sucrose and macronutrients absorption and promotes autotrophy in the <Emphasis Type="Italic">in vitro</Emphasis> culture of kiwi (<Emphasis Type="Italic">Actinidia deliciosa</Emphasis> Chev. Liang and Ferguson)

In traditional in vitro culture, the low CO₂ concentration inside the vessels restricts photosynthesis and necessitates the addition of sucrose to the culture medium as the main energy source, thus bringing about changes in the absorption of mineral elements from the culture medium. In this study, we investigated macronutrient absorption and sugar consumption in Actinidia deliciosa Chevalier Liang and Ferguson cv. Hayward (kiwi), cultured on medium supplemented with varying amounts of sucrose (0, 10, and 20 g l⁻¹) under both heterotrophy and autotrophy, flushed with different concentrations of CO₂ (non-ventilation, 300, 600, and 2,000 μl l⁻¹). In ventilated systems with 20 g l⁻¹ of sucrose, sucrose absorption was less than under non-ventilation. The lowest rate of sucrose absorption was recorded when the explants were cultured on medium supplemented with 20 g l⁻¹ of sucrose and flushed with 600 μl l⁻¹ CO₂. Absorption of NO₃ ⁻, PO₄ ³⁻, and Mg²⁺ were high (maximum) at the end of the culture period (40 d) in explants flushed with 600 μl l⁻¹ CO₂ that have been cultured 20 d in the presence of sucrose and then transferred to a sucrose-free medium. These autotrophic conditions promoted maximum plant growth in terms of both fresh and dry mass as well as the length and number of shoots and leaves. The study shows that to maintain an optimum regime of mineral nutrition for prolonged culture of kiwi in vitro, an increased amount of these three ions should be supplemented in Murashige and Skoog’s medium.     

Physiological differences in the growth of <Emphasis Type="Italic">Sargassum horneri</Emphasis> between the germling and adult stages

The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance (10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m⁻²s⁻¹) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m⁻²s⁻¹), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day⁻¹ (25°C, 20 μmol photons m⁻²s⁻¹) and 13% day⁻¹ (8 h daylength). In contrast, the RGRs of the blade weights were 4% day⁻¹ (15°C, 20 μmol photons m⁻²s⁻¹) and 5% day⁻¹ (12 h daylength). Negative growth rates were found at 20 μmol photons m⁻²s⁻¹ of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m⁻²s⁻¹, and 8 h daylength for construction of Sargassum beds and restoration of barren areas.     

Seasonal dynamics of soil CO<Subscript>2</Subscript> efflux in a conventional tilled wheat field of the Loess Plateau,China

An automated chamber system was employed to measure the soil CO₂ efflux (SCE) in situ for 2 years in a conventional wheat field of the Loess Plateau, China under semi-arid conditions. The annual mean SCE values were 2.44 ± 2.52 μmol m⁻² s⁻¹ in 2006 and 2.37 ± 2.33 μmol m⁻² s⁻¹ in 2007. Distinct seasonality in the SCE was observed, with significant differences occurring among four periods divided by harvesting, tillage and sowing. In the period from tillage to sowing, the mean SCE values were 2.82 and 2.69 times the annual mean values in 2006 and 2007, respectively, and SCE accounted for 39% and 48% of the annual total within 14% and 18% of the days of the years. Although there were significant exponential correlations between the SCE and soil temperature, and significant linear correlations between the SCE and soil moisture for measurements conducted in the periods before tillage and after sowing each year, the SCE from tillage to sowing was significantly beyond the correlation curves. These findings indicated that seasonal variation in the SCE in a conventional field was controlled not only by soil temperature and moisture, but also by tillage practice. The confounding effects of climate and practice on SCE should be considered when developing ways to mitigate soil carbon loss in conventional cropland in semi-arid regions.     

HMG-CoA reductase limits artemisinin biosynthesis and accumulation in <Emphasis Type="Italic">Artemisia annua</Emphasis> L. plants

In vivo modulation of HMG-CoA reductase (HMGR) activity and its impact on artemisinin biosynthesis as well as accumulation were studied through exogenous supply of labeled HMG-CoA (substrate), labeled MVA (the product), and mevinolin (the competitive inhibitor) using twigs of Artemisia annua L. plants collected at the pre-flowering stage. By increasing the concentration (2–16 μM) of HMG-CoA (3-¹⁴C), incorporation of labeled carbon into artemisinin was enhanced from 7.5 to 17.3 nmol (up to 130%). The incorporation of label (¹⁴C) into MVA and artemisinin was inhibited up to 87.5 and 82.9%, respectively, in the presence of 200 μM mevinolin in incubation medium containing 12 μM HMG-CoA (3-¹⁴C). Interestingly, by increasing the concentration of MVA (2-¹⁴C) from 2 to 18 μM, incorporation of label (¹⁴C) into artemisinin was enhanced from 10.5 to 35 nmol (up to 233%). When HMG-CoA (3-¹⁴C) concentration was increased from 12 to 28 μM in the presence of 150 μM mevinolin, the inhibitions in the incorporation of label (¹⁴C) into MVA and artemisinin were, however, reversed and the labels were found to approach their values in twigs fed with 12 μM HMG-CoA (3-¹⁴C) without mevinolin. In another experiment, 14.2% inhibition in artemisinin accumulation was observed in twigs in the presence of 175 μM fosmidomycin, the competitive inhibitor of 1-deoxy-d-xylulose 5-phosphate reductase (DXR). HMG-CoA reductase activity and artemisinin accumulation were also increased by 18.6 to 24.5% and 30.7 to 38.4%, respectively, after 12 h of treatment, when growth hormones IAA (100 ppm), GA₃ (100 ppm) and IAA + GA₃ (50 + 50 ppm) were sprayed on A. annua plants at the pre-flowering stage. The results obtained in this study, hence, demonstrate that the mevalonate pathway is the major contributor of carbon supply to artemisinin biosynthesis and HMGR limits artemisinin synthesis and its accumulation in A. annua plants.     

Process-level controls on CO<Subscript>2</Subscript> fluxes from a seasonally snow-covered subalpine meadow soil,Niwot Ridge,Colorado

Fluxes of CO₂ during the snow-covered season contribute to annual carbon budgets, but our understanding of the mechanisms controlling the seasonal pattern and magnitude of carbon emissions in seasonally snow-covered areas is still developing. In a subalpine meadow on Niwot Ridge, Colorado, soil CO₂ fluxes were quantified with the gradient method through the snowpack in winter 2006 and 2007 and with chamber measurements during summer 2007. The CO₂ fluxes of 0.71 μmol m⁻² s⁻¹ in 2006 and 0.86 μmol m⁻² s⁻¹ in 2007 are among the highest reported for snow-covered ecosystems in the literature. These fluxes resulted in 156 and 189 g C m⁻² emitted over the winter, ~30% of the annual soil CO₂ efflux at this site. In general, the CO₂ flux increased during the winter as soil moisture increased. A conceptual model was developed with distinct snow cover zones to describe this as well as the three other reported temporal patterns in CO₂ flux from seasonally snow-covered soils. As snow depth and duration increase, the factor controlling the CO₂ flux shifts from freeze–thaw cycles (zone I) to soil temperature (zone II) to soil moisture (zone III) to carbon availability (zone IV). The temporal pattern in CO₂ flux in each zone changes from periodic pulses of CO₂ during thaw events (zone I), to CO₂ fluxes reaching a minimum when soil temperatures are lowest in mid-winter (zone II), to CO₂ fluxes increasing gradually as soil moisture increases (zone III), to CO₂ fluxes decreasing as available carbon is consumed. This model predicts that interannual variability in snow cover or directional shifts in climate may result in dramatically different seasonal patterns of CO₂ flux from seasonally snow-covered soils.     

Effects of elevated CO<Subscript>2</Subscript> and/or O<Subscript>3</Subscript> on hormone IAA in needles of Chinese pine

This study examined the effects of season-long exposure of Chinese pine (Pinus tabulaeformis) to elevated carbon dioxide (CO₂) and/or ozone (O₃) on indole-3-acetic acid (IAA) content, activities of IAA oxidase (IAAO) and peroxidase (POD) in needles. Trees grown in open-top chambers (OTC) were exposed to control (ambient O₃, 55 nmol mol⁻¹ + ambient CO₂, 350 μmol mol⁻¹, CK), elevated CO₂ (ambient O₃ + high CO₂, 700 μmol mol⁻¹, EC) and elevated O₃ (high O₃, 80 ± 8 nmol mol⁻¹ + ambient CO₂, EO) OTCs from 1 June to 30 September. Plants grown in elevated CO₂ OTC had a growth increase of axial shoot and needle length, compared to control, by 20% and 10% respectively, while the growth in elevated O₃ OTC was 43% and 7% less respectively, than control. An increase in IAA content and POD activity and decrease in IAAO activity were observed in trees exposed to elevated CO₂ concentration compared with control. Elevated O₃ decreased IAA content and had no significant effect on IAAO activity, but significantly increased POD activity. When trees pre-exposed to elevated CO₂ were transferred to elevated O₃ (EC–EO) or trees pre-exposed to elevated O₃ were transferred to elevated CO₂ (EO–EC), IAA content was lower while IAAO activity was higher than that transferred to CK (EC–CK or EO–CK), the change in IAA content was also related to IAAO activity. The results indicated that IAAO and POD activities in Chinese pine needles may be affected by the changes in the atmospheric environment, resulting in the change of IAA metabolism which in turn may cause changes in Chinese pine’s growth. An erratum to this article can be found at     

Genetic variation of <Emphasis Type="Italic">Fusarium oxysporum</Emphasis> isolates forming fumonisin B<Subscript>1</Subscript> and moniliformin

Thirty single-spore isolates of a toxigenic fungus, Fusarium oxysporum, were isolated from asparagus spears and identified by species-specific polymerase chain reaction (PCR) and translation elongation factor 1-α (TEF) sequence analysis. In the examined sets of F. oxysporum isolates, the DNA sequences of mating type genes (MAT) were identified. The distribution of MAT idiomorph may suggest that MAT1-2 is a predominant mating type in the F. oxysporum population. F. oxysporum is mainly recognised as a producer of moniliformin—the highly toxic secondary metabolite. Moniliformin content was determined by high-performance liquid chromatography (HPLC) analysis in the range 0.05–1,007.47 μg g⁻¹ (mean 115.93 μg g⁻¹) but, also, fumonisin B₁ was detected, in the concentration range 0.01–0.91 μg g⁻¹ (mean 0.19 μg g⁻¹). There was no association between mating types and the mycotoxins biosynthesis level. Additionally, a significant intra-species genetic diversity was revealed and molecular markers associated with toxins biosynthesis were identified.     

Antivibrio compounds produced by <Emphasis Type="Italic">Pseudomonas</Emphasis> sp. W3: characterisation and assessment of their safety to shrimps

In order to explore compounds naturallly inhibitory to shrimp pathogenic vibrios, a culture filtrate of Pseudomonas sp. W3 at a pH of 2 was extracted with ethyl acetate (EtOAc) to produce 82.15 mg/l of a yellow–brown extract (EtOAc-W3) that had MIC values of 225-450 μg/ml against the growth of 18 shrimp pathogenic Vibrio harveyi strains. The MIC of EtOAc-W3 against the most pathogenic strain PSU 2015 was 450 μg/ml and this strain had the lowest LD₅₀ (50% lethal dose) to pacific white shrimp (Litopenaeus vannamei, PL 21). At this MIC value, EtOAc-W3 in artificial sea water (ASW) killed strain PSU 2015; however in natural sea water, only a partial growth inhibition was observed. The toxicity to pacific white shrimp and antivibrio activity of the EtOAc-W3 were investigated by conducting an experiment with 4 sets; native control (commercial ASW), EtOAc-W3 control (MIC/10, 45 μg/ml), challenge (inoculation 6.0 × 10⁶ c.f.u./ml PSU 2015) and treatment (6.0 × 10⁶ c.f.u./ml PSU 2015 + 45 μg/ml EtOAc-W3). The same experiment was repeated by increasing the dose of EtOAc-W3 to 90 μg/ml (MIC/5). Both concentrations of EtOAc-W3 tested had no toxicity to postlarval shrimps. A significant decrease in shrimp mortality was observed over a 72 h period as approximately 80% of the shrimps died in each challenge set but only 63 and 23% died in the presence of 45 and 90 μg/ml EtOAc-W3. The major component of EtOAc-W3 was supposed to be 2-heptyl-4-quinolone (HHQ) by FAB-MS and ¹H-NMR analyses of the purified fraction.     

The effects of elevated atmospheric [CO<Subscript>2</Subscript>] on Norway spruce needle parameters

Studies of selected morphological needle parameters were carried out on young (17–19 year old) Norway spruce trees cultivated inside glass domes at ambient (A, 370 μmol (CO₂) mol⁻¹) and elevated (E, 700 μmol (CO₂) mol⁻¹) atmospheric CO₂ concentrations [CO₂] beginning in 1997. Annual analyses performed from 2002 to 2004 revealed higher values for needle length (especially for current needles, up to 18%) and projected needle area (up to 13%) accompanied by lower values for specific needle area (up to 15% lower, as quantified by needle mass to projected area ratio) in the E treatment compared to the A treatment. Statistically significant differences for most of the investigated morphological parameters were found in young needles in the well irradiated sun-adapted crown parts, particularly under water-limiting soil conditions in 2003. This was likely a result of different water relations in E compared to A trees as investigated under temperate water stress (Kuper et al. in Biol Plantarum 50:603–609, 2006). Furthermore, E trees had much higher absorbing root area, which modified and enhanced root:shoot as well as root:conductive stem area proportions. These hydraulic properties and early seasonal stimulation of photosynthesis forced advanced needle development in E trees, particularly under limited soil water conditions. The number of needles per unit shoot length was found to be unaffected by elevated [CO₂].