Sensibilität von Plasmodium vivax gegenüber Klasse-2- Blutschizontoziden und Artemisinin

Diese in vitro Studie über die Arzneimittelempfindlichkeit von Plasmodium vivax im Nordwesten Thailands wurde 2009/2010 in Wien anhand von Material aus Mae Sot durchgeführt. Insgesamt wurden 46 Patientenproben erfolgreich auf ihre in vitro Sensibilität gegenüber den Präparaten Artemisinin, Atovaquon und Desbutyl- Benflumentol getestet. Dies wurde mittels des speziell für Plasmodium vivax entwickelten Testverfahrens von Tasanor et al. (2002) durchgeführt. Für Artemisinin wurden von Herrn Prof. Wernsdorfer Vergleichsdaten aus dem Jahr 2004 zu Verfügung gestellt. Beim Vergleich der Parameter der beiden Jahre zeigte sich, dass die IC50 und IC90 Werte für die getesteten Präparate von 2004 höher lagen, jedoch lag der IC99 Wert von 2007 höher als jener von 2004. Die Verringerung der Artemisininempfindlichkeit drückt sich auch in der Abflachung der Regressionsgeraden auf. Dies weist auf eine Verschlechterung der Sensibilität gegenüber Artemisinin hin. Die Korrelation mit den anderen Medikamenten zeigt bei den log-transformierten Messdaten Signifikanz zwischen der Aktivität von Artemisinin und den Medikamenten Atovaquon und Desbutyl- Benflumentol. Der Korrelationskoeffizient der IC50 Werte lag für die log-transformierten Daten für Artemisinin und Atovaquon knapp unter der Signifikanzgrenze.Für Artemisinin und Desbutyl-Benflumetol lag er weit unter der Signifikanzgrenze. ebenso bei Artemisinin und Desbutyl-Benflumentol, während die Ergebnisse für Atovaquon und Desbutyl-Benflumetol signifikant korrelierten, Mit den log-transformierten IC90 und IC99 Werten lagen die Korrelationskoeffizienten sämtlicher Vergleiche zwischen Artemisinin, Atovaquon und Desbutyl-Benflumetol über der Signifikanzgrenze (p < 0,05). Zwischen den drei getesteten Medikamenten liegt keine enge strukturelle Verwandtschaft vor, doch gelten Atovaquon und Desbutyl-Benflumetol als Klasse-2 Blutschizontozide und Artemisinin hat Wirkungskorrelation mit anderen Klasse-2 Blutschizontoziden. Daher sind diese Ergebnisse möglicherweise auf eine ähnliche Wirkungsweise zurückzuführen. Es könnte auch ein Indiz dafür sein, dass man mit Kreuzresistenzen bei Artemisinin rechnen muss. Auf molarer Basis lag der Mittelwert der IC50 für Artemisinin zwischen jenen der beiden anderen getesteten Medikamente, die IC90 und IC99 Werte für Artemisinin waren jedoch die geringsten. Am höchsten waren die IC-Werte für Atovaquon. Der Steigungsindex der Regressionsgeraden liegt für Artemisinin und Atovaquon bei 13,0010 und 13,3346, diese Werte sind sehr ähnlich. Bei Desbutyl- Benflumentol liegt er nur wenig höher, bei einem Wert von 15,6717. Auch der Grad der Steigung (b) ist bei allen drei Medikamenten in etwa gleich, was zu ähnlich steilen Regressionsgerade führt.This in vitro response study of Plasmodium vivax to artemisinine, atovaquone and desbutyl-benflumentol was performed in Vienna with material from the malaria clinic in Mae Sot (Thailand). In total, 46 isolates were successfully tested. The sensitivity pattern shows a log-concentration normal distribution for all three drugs. The study indicates a significant activity correlation between artemisinin and the two other drugs at the IC-90 and IC-99 of the log-transformed results. The significant correlation suggests similarities in the mechanism of action between these drugs, and the possibility of multi-drug resistance in the future. Comparison between the results for artemisinin from the year 2004 and 2007 shows a reduction in drug sensitivity. This also may also indicate the development of manifest resistance against artemisinin in the not too distant future. The correlation of between the activities of atovaquone and desbutyl- benflumentol was highly significant even for the non-transformed results. The higher-level ICs for artemisinin are lower than the ICs of the two other drugs which show that P. vivax is, on a mol/mol basis, more sensitive to artemisinin than to the two other compounds

An improved method for the visualization of conductive vessels in Arabidopsis thaliana inflorescence stems

Dye perfusion is commonly used for the identification of conductive elements important for the study of xylem development as well as precise hydraulic estimations. The tiny size of inflorescence stems, the small amount of vessels in close arrangement, and high hydraulic resistivity delimit the use of the method for quantification of the water conductivity of Arabidopsis thaliana, one of the recently most extensively used plant models. Here, we present an extensive adjustment to the method in order to reliably identify individual functional (conductive) vessels. Segments of inflorescence stems were sealed in silicone tubes to prevent damage and perfused with a dye solution. Our results showed that dyes often used for staining functional xylem elements (safranin, fuchsine, toluidine blue) failed with Arabidopsis. In contrast, Fluorescent Brightener 28 dye solution perfused through segments stained secondary cell walls of functional vessels, which were clearly distinguishable in native cross sections. When compared to identification based on the degree of development of secondary cell walls, identification with the help of dye perfusion revealed a significantly lower number of functional vessels and values of theoretical hydraulic conductivity. We found that lignified but not yet functional vessels form a substantial portion of the xylem in apical and basal segments of Arabidopsis and, thus, significantly affect the analyzed functional parameters of xylem. The presented methodology enables reliable identification of individual functional vessels, allowing thus estimations of hydraulic conductivities to be improved, size distributions and vessel diameters to be refined, and data variability generally to be reduced

Soil mineral nitrogen availability was unaffected by elevated atmospheric pCO2 in a four year old field experiment (Swiss FACE)

The effect of elevated (60 Pa) atmospheric carbon dioxide partial pressure (pCO2) and N fertilisation on the availability of mineral N and on N transformation in the soil of a Lolium perenne L. monoculture was investigated in the Swiss FACE (Free Air Carbon dioxide Enrichment) experiment. The apparent availability of nitrate and ammonium for plants was estimated during a representative, vegetative re-growth period at weekly intervals from the sorption of the minerals to mixed-bed ion-exchange resin bags at a soil depth of 5 cm. N mineralisation was measured using sequential coring and in situ exposure of soil cores in the top 10 cm of the soil before and after the first cut in spring 1997. High amounts of mineral N were bound to the ion exchange resin during the first week of re-growth. This was probably the combined result of the fertiliser application, the weak demand for N by the newly cut sward and presumably high rates of root decay and exudation after cutting the sward. During the first 2 weeks after the application of fertiliser N at the first cut, there was a dramatic reduction in available N; N remained low during the subsequent weeks of re-growth in all treatments. Overall, nitrate was the predominant form of mineral N that bound to the resin for the duration of the experiment. Apparently, there was always more nitrate than ammonium available to the plants in the high N fertilisation treatment for the whole re-growth period. Apparent N availability was affected significantly by elevated pCO2 only in the first week after the cut; under high N fertilisation, elevated pCO2 increased the amount of mineral N that was apparently available to the plants. Elevated pCO2 did not affect apparent net transformation of N, loss of N or uptake of N by plants. The present data are consistent with earlier results and suggest that the amount of N available to plants from soil resources does not generally increase under elevated atmospheric pCO2. Thus, a possible limiting effect of N on primary production could become more stringent under elevated atmospheric pCO2 as the demand of the plant for N increase

Early Changes in Nitrate Uptake and Assimilation Under Drought in Relation to Transpiration

Soil drying combined with nitrogen (N) deficiency poses a grave threat to agricultural crop production. The rate at which nitrate (NO3−) is taken up depends partly on the uptake and transpiration of water. Rapid changes in nitrate assimilation, in contrast to other N forms, may serve as a component of the plant stress response to drought because nitrate assimilation may lead to changes in xylem pH. The modulation of xylem sap pH may be relevant for stomata regulation via the delivery of abscisic acid (ABA) to guard cells. In several factorial experiments, we investigated the interactions between nitrate and water availability on nitrate fate in the plant, as well as their possible implications for the early drought-stress response. We monitored the short-term response (2–6 days) of nitrate in biomass, transport to shoot and reduction in Pisum sativum, Hordeum vulgare, Vicia faba, and Nicotiana tabacum and correlated this with sap pH and transpiration rates (TRs). Cultivation on inorganic substrate ensured control over nutrient and water supply and prevented nodulation in legume species. NO3− content in biomass decreased in most of the species under drought indicating significant decline in NO3− uptake. Hordeum vulgare had the highest NO3− concentrations in all organs even under drought and low NO3− treatment. This species can likely respond much better to the combined adverse effects of low NO3− and water scarcity. Nitrate reductase activity (NRA) was reduced in both roots and leaves of water deficient (WD) plants in all species except H. vulgare, presumably due to its high NO3− contents. Further, transient reduction in NO3− availability had no effect on sap pH. Therefore, it seems unlikely that NRA shifts from shoot root leading to the supposed alkalization of sap. We also did not observe any interactive effects of NO3− and water deficiency on transpiration. Hence, as long as leaf NO3− content remains stable, NO3− availability in soil is not linked to short-term modulation of transpiration.Peer Reviewe

Session 17 Ecophysiology

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