Effects of UV-B radiation on terrestrial plants and ecosystems: interaction with CO2 enrichment

UV-B radiation is just one of the environmental factors, that affect plant growth. It is now widely accepted that realistic assessment of plant responses to enhanced UV-B should be performed at sufficiently high Photosynthetically Active Radiation (PAR), preferably under field conditions. This will often imply, that responses of plants to enhanced UV-B in the field will be assessed under simultaneous water shortage, nutrient deficiency and variation of temperature. Since atmospheric CO₂ enrichment, global warming and increasing UV-B radiation represent components of global climatic change, interactions of UV-B with CO₂ enrichment and temperature are particularly relevant. Only few relevant UV-B× CO₂ interaction studies have been published. Most of these studies refer to greenhouse experiments. We report a significant CO₂ × UV-B interaction for the total plant dry weight and root dry weight of the C₃-grass Elymus athericus. At elevated CO₂ (720 mol mol^-1, plant growth was much less reduced by enhanced UV-B than at ambient atmospheric CO₂ although there were significant (positive) CO₂ effects and (negative) UV-B effects on plant growth. Most other CO₂ × UV-B studies do not report significant interactions on total plant biomass. This lack of CO₂ × UV-B interactions may result from the fact that primary metabolic targets for CO₂ and UVB are different. UV-B and CO₂ may differentially affect plant morphogenetic parameters: biomass allocation, branching, flowering, leaf thickness, emergence and senescence. Such more subtle interactions between CO₂ and UV-B need careful and long term experimentation to be detected. In the case of no significant CO₂× UV-B interactions, combined CO₂ and UV-B effects will be additive. Plants differ in their response to CO₂ and UV-B, they respond in general positively to elevated CO₂ and negatively to enhanced UV-B. Moreover, plant species differ in their responsiveness to CO₂ and UV-B. Therefore, even in case of additive CO₂ and UV-B effects, plant competitive relationships may change markedly under current climatic change with simultaneous enhanced atmospheric CO₂ and solar UV-B radiation.     

Improve protective efficacy of a TB DNA-HSP65 vaccine by BCG priming

Vaccines are considered by many to be one of the most successful medical interventions against infectious diseases. But many significant obstacles remain, such as optimizing DNA vaccines for use in humans or large animals. The amount of doses, route and easiness of administration are also important points to consider in the design of new DNA vaccines. Heterologous prime-boost regimens probably represent the best hope for an improved DNA vaccine strategy. In this study, we have shown that heterologous prime-boost vaccination against tuberculosis (TB) using intranasal BCG priming/DNA-HSP65 boosting (BCGin/DNA) provided significantly greater protection than that afforded by a single subcutaneous or intranasal dose of BCG. In addition, BCGin/DNA immunization was also more efficient in controlling bacterial loads than were the other prime-boost schedules evaluated or three doses of DNA-HSP65 as a naked DNA. The single dose of DNA-HSP65 booster enhanced the immunogenicity of a single subcutaneous BCG vaccination, as evidenced by the significantly higher serum levels of anti-Hsp65 IgG2a Th1-induced antibodies, as well as by the significantly greater production of IFN-γ by antigen-specific spleen cells. The BCG prime/DNA-HSP65 booster was also associated with better preservation of lung parenchyma. The improvement of the protective effect of BCG vaccine mediated by a DNA-HSP65 booster suggests that our strategy may hold promise as a safe and effective vaccine against TB.     

Differential response of salt-marsh species to variation of iron and manganese

Salt-marsh plants of the lower, middle and upper marsh were compared in their response to iron and manganese. The species studied showed differential sensitivity to high concentrations of Fe (1 000 μM) and Mn (10 000 μM) in hydroculture experiments, species of the lower marsh being more resistant than species of the upper marsh. Fe and Mn concentrations in the root were higher than in the shoot, which was also found in plants inundated with seawater. High Fe and Mn concentrations in the root are probably the result of the oxidizing power of plant roots with a subsequent low translocation of Fe (II) and Mn (II) to the shoot. At high (toxic) Fe and Mn levels in the nutrient solution, Fe and Mn concentrations were much higher in the shoots of sensitive species than in resistant species. The P content of roots and shoots was not influenced by increased Fe and Mn concentrations. Fe and Mn resistance in Spartina anglica and Juncus gerardii, may be in part due to a high root porosity. Other species, however, that are similarly resistant to Fe and Mn lack a well-developed aerenchym. Root porosity, radial oxygen loss and Fe (II) and Mn (II) exclusion by oxidation to Fe (III) (hydr)oxides deposited on the roots form part of the resistance mechanism of hygrohalophytes to Fe and Mn; the differences in this respect between the species may also be due to other metabolic aspects.     

No divergence in Cassiope tetragona: persistence of growth response along a latitudinal temperature gradient and under multi-year experimental warming

Background and Aims

The dwarf shrub Cassiope tetragona (Arctic bell-heather) is increasingly used for arctic climate reconstructions, the reliability of which depends on the existence of a linear climate–growth relationship. This relationship was examined over a high-arctic to sub-arctic temperature gradient and under multi-year artificial warming at a high-arctic site.

Methods

Growth chronologies of annual shoot length, as well as total leaf length, number of leaves and average leaf length per year, were constructed for three sites. Cassiope tetragona was sampled near its cold tolerance limit at Ny-Ålesund, Svalbard, at its assumed climatic optimum in Endalen, Svalbard, and near its European southern limit at Abisko, Sweden. Together these sites represent the entire temperature gradient of this species. Leaf life span was also determined. Each growing season from 2004 to 2010, 17 open top chambers (OTCs) were placed near Ny-Ålesund, thus increasing the daily mean temperatures by 1·23°C. At the end of the 2010 growing season, shoots were harvested from OTCs and control plots, and growth parameters were measured.

Key Results

All growth parameters, except average leaf length, exhibited a linear positive response (R² between 0·63 and 0·91) to mean July temperature over the temperature gradient. Average leaf life span was 1·4 years shorter in sub-arctic Sweden compared with arctic Svalbard. All growth parameters increased in response to the experimental warming; the leaf life span was, however, not significantly affected by OTC warming.

Conclusions

The linear July temperature–growth relationships, as well as the 7 year effect of experimental warming, confirm that the growth parameters annual shoot length, total leaf length and number of leaves per year can reliably be used for monitoring and reconstructing temperature changes. Furthermore, reconstructing July temperature from these parameters is not hampered by divergence.     

Mass of weaned elephant seal pups in areas of low and high human presence

On sub-Antarctic Macquarie Island, we examined pup weaning mass of southern elephant seals in relation to human presence. Pup weaning mass was previously found to be positively associated with 1st-year survivorship. Weaned pups were weighed in a remote area, Middle Beach, and in an area of relatively high human presence, Isthmus East. The areas were reasonably similar in beach topography, wind and surf conditions, numbers of seals present per kilometre of coastline, and numbers of males and females present in harems. For a sub-sample of measured pups, data on the respective maternal size were collected using photogrammetry. Both male and female weaned pups on Middle Beach were significantly heavier than those on Isthmus East. Estimated length of mothers was significantly higher on Middle Beach. In proportion to their own size, mothers in both areas produced weaners of similar mass, indicating no direct effect of human disturbance on the efficiency of lactation. It remained unclear whether the area differences in maternal and pup size were due to natural or human-related factors.     

"Silent" sites in Drosophila genes are not neutral: evidence of selection among synonymous codons

The patterns of synonymous codon usage in 91 Drosophila melanogaster genes have been examined. Codon usage varies strikingly among genes. This variation is associated with differences in G+C content at silent sites, but (unlike the situation in mammalian genes) these differences are not correlated with variation in intron base composition and so are not easily explicable in terms of mutational biases. Instead, those genes with high G+C content at silent sites, resulting from a strong "preference" for a particular subset of the codons that are mostly C- ending, appear to be the more highly expressed genes. This suggests that G+C content is reduced in sequences where selective constraints are weaker, as indeed seen in a pseudogene. These and other data discussed are consistent with the effects of translational selection among synonymous codons, as seen in unicellular organisms. The existence of selective constraints on silent substitutions, which may vary in strength among genes, has implications for the use of silent molecular clocks.      

Two levels of resting potential in cardiac purkinje fibers

In an appropriate ionic environment, the resting potential of canine cardiac purkinje fibers may have either of two value. By changing the external K concentration, [K](0), in small steps, it was shown that, in the low (1 mM) Cl, Na-containing solutions used in this study, the two levels of resting potential could be obtained only within a narrow range of [K](0) values; that range was usually found between 1 and 4 mM. Within the critical [K](0) range the resting potential could be shifted from either level to the other by the application of small current pulses. It was shown that under these conditions the steady-state current- voltage relationship was “N-shaped,” and that a region of both negative slope, and negative chord conductance lay between the two stable zero-current potentials. The negative chord conductance was largely due to inward sodium current, only part of which was sensitive to tetrodotoxin (TTX). Under appropriate conditions, the negative chord conductance could be abolished by several experimental interventions and the membrane potential thereby shifted from the lower to the higher resting level: those interventions which were effective by presumably diminishing the steady-state inward current included reducing the external sodium concentration, adding TTX, or adding lidocaine; those which presumably increased the steady-state outward current included small increases in [K](0), brief depolarizations to around -20 mV, or the addition of acetylcholine chloride.     

Cell-type specificity of ectonucleotidase expression and upregulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin

We report here that induction of ectoATPase by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is cell-type specific and not a generalized response to aryl hydrocarbon (Ah) receptor activation. TCDD increased [14C]-ATP and -ADP metabolism in two mouse hepatoma lines, Hepa1c1c7 and Hepa1-6 cells, but not in human hepatoma HepG2 or HuH-7 cells, human umbilical vein endothelial cells (HUVEC), chick hepatoma (LMH) cells, or chick primary hepatocytes or cardiac myocytes, even though all of those cell types were Ah receptor-responsive, as evidenced by cytochrome P4501A induction. To determine whether the differences in ectonucleotidase responsiveness to TCDD might be related to differences in cell-type ectonucleotidase expression, ATP and ADP metabolite patterns, the products of several classes of ectonucleotidases including ectonucleoside triphosphate diphosphohydrolases (E-NTPDases), ectophosphodiesterase/pyrophosphatases (E-NPP enzymes) and ectoalkaline phosphatase activities were examined. Those patterns, together with results of enzyme assays, Western blotting, or semiquantitative RT-PCR show that NTPDase2 is the main ectonucleotidase for murine and human hepatoma cells, NTPDase3 for chick hepatocytes and LMH cells, and an E-NPP enzyme for chick cardiac myocytes. Evidence for NTPDase2 expression was lacking in all cells except the mouse and human hepatoma cells. TCDD increased expression of the NTPDase2 gene but only in the mouse and not in the human hepatoma cells. TCDD did not increase NTPDase3, NTPDase1, E-NPP, or alkaline phosphatase in any of the cell types examined. The failure of TCDD to increase ATP metabolism in HUVEC, chick LMH cells, hepatocytes, and cardiac myocytes can be attributed to their lack of NTPDase2 expression, while the increase in ATP metabolism by TCDD in the mouse but not the human hepatoma cells can be explained by differences in TCDD effects on mouse and human hepatoma NTPDase2 gene expression. In addition to characterizing effects of TCDD on ectonucleotidases, these studies reveal major differences in the complements of ectonucleotidases present in different cell types. It is likely that such differences are important for cell-specific susceptibility to extracellular nucleotide toxicity and responses to purinergic signaling.     

Changes in phosphatidylinositol and phosphatidic acid in stimulated human neutrophils. Relationship to calcium mobilization, aggregation and superoxide radical generation

Human neutrophils aggregate and release mediators of inflammation, such as active oxygen species and lysosomal enzymes, when exposed to the chemoattractant, fMet-Leu-Phe, or the tumor promotor, phorbol myristate acetate. In order to 'stage' events which may lead to such neutrophil responses, we determined the temporal relationship between stimulus-induced changes in the endogenous phospholipids phosphatidylinositol (PI) and phosphatidic acid, the mobilization of calcium, and the onset of aggregation and generation of superoxide anion during the initial 2 min of cell activation. Within 5 s after addition of fMet-Leu-Phe (10(-7) M) neutrophils accumulated phosphatidic acid and the levels of PI decreased, as determined by two-dimensional thin-layer chromatography and phosphorus determinations. By 5 s, phosphatidic acid levels rose approximately 3.5-fold and at 15 s the loss of PI exceeded the quantity of phosphatidic acid generated. In response to phorbol myristate acetate (1 microgram/ml), however, changes in PI or phosphatidic acid were not observed until after 60 s. Accumulation of phosphatidic acid in fMet-Leu-Phe-stimulated cells was not inhibited by chelation of extracellular calcium. Neutrophils exposed to either fMet-Leu-Phe or phorbol myristate acetate also showed rapid decrements in fluorescence of cell-associated chlorotetracycline (used as an indirect probe of mobilization of intracellular membrane-associated calcium) and took up 45Ca2+ from the extracellular medium (under 60 s). The results indicate that changes in calcium mobilization, together with the alterations in phospholipid metabolism (under 5 s) anteceded aggregation and the generation of O2-. (10-15 s) induced by fMet-Leu-Phe. In contrast, when neutrophils were exposed to phorbol myristate acetate, changes in PI and phosphatidic acid (over 60 s) were observed after the mobilization of calcium (under 5 s) and the onset of O2-. generation and aggregation (30-35 s).     

Formation of leukotrienes and other hydroxy acids during platelet-neutrophil interactions in vitro

Interactions of human platelets with neutrophils were studied in suspensions of [³H]arachidonate-labeled platelets and unlabeled neutrophils stimulated with ionophore A23187. Several radioactive arachidonate metabolites, not produced by platelets alone, were detected, including [³H]-labeled leukotriene B₄ (LTB₄), dihydroxyeicosatetraenoic acid (DHETE) and 5-hydroxyeicosatetraenoic acid (5-HETE). When [³H]12-HETE, a platelet product, was added to stimulated neutrophils, DHETE was formed. Similarly, when [³H]5-HETE, a neutrophil product, was added to stimulated platelets, DHETE was the major product. These results suggest that upon stimulation: 1) platelet-derived arachidonate may serve as precursor for the neutrophil-derived eicosanoids LTB₄ and 5-HETE, and 2) that platelet-derived 12-HETE can be converted to DHETE by human neutrophils. The present investigation documents cell-cell interactions via the lipoxygenase pathway, which may be important in hemostasis, thrombosis and inflammation.