Effet des variations d'énergie lumineuse associées à l'agitation verticale sur le bilan photosynthétique de cultures intensives d'algues en bassin

Une série d'expériences a été réalisée pour évaluer les effets de l'agitation sur le bilan photosynthétique de cultures d'algues en masse en bassins extérieurs. La méthode utilisée compare la production d'échantillons marqués au C14 disposés (1) selon un profil vertical classique, (2) sur un système rotatif faisant transiter un flacon entre la surface et le tond du bassin. Des mesures ont été effectuées périodiquement en milieu de journée sur un cycle annuel, et ont été complétées par 8 incubations réalisées entre le lever et le coucher du soleil pour un jour donné. Dans toutes les expériences réalisées durant la période estivale, la photosynthèse est supérieure dans le flacon mobile. Les effets des variations lumineuses (par le biais des mouvements de l'eau) sur te bilan photosynthétique de la colonne d'eau sont particulièrement notables au lever et au coucher du soleil; ce bilan peut être jusqu'à 2.5 fois plus important pour une colonne d'eau en mouvement. Le calcul d'un bilan journalier par extrapolation des profils de photosynthèse instantanés permet d'estimer le gain de production obtenu par agitation du milieu. Par contre pendant la période hivernale, la photosynthèse est supérieure dans le flacon immobile. Ces résultats ont des implications évidentes sur le monitoring de cultures d'algues en masse en bassins extérieurs.Experiments were carried out to define the effect of a particular mixing system (circular round a horizontal axis) upon the primary productivity of high-rate alga cultures. We know that mixing prevent algal cell sedimentation, gaseous and nutritional gradients, and variations in algae light reception. So, we wanted to quantity the effect of mixing on algal productivity with regard to flashing light (positive effect in comparison with continuous light).We used water from waste stabilization ponds (secondary pond output), with the native algae population dominated by Euglena and Chlorella (in Aveyron, South of France). The method used compares algal production of a water column with 14C-labelled samples i) in ten flasks placed along a classical vertical profile, ii) in a rotating system with a flask moving between the top and the bottom of the pond (0.5 m). The production is here considered as the mean of a mixed vertical profile. At the same time, physico-chemical and biological parameters were recorded (high load for N and P).Experiments were made periodically in the mid-afternoon over one year, and were completed by 8 incubations made between sunrise and sunset for on day (in August 1989). The aim was to evaluate the mixing affect with various environmental conditions. Physico-chemical parameters vary greatly over a day, and higher production values are measured in the mid-afternoon. Production observed for the stationary profile fitted the Steele model, and showed active photosynthetic from sunrise until sunset, with inhibition at high light intensities; maximal photosynthesis rates were measured between 4.00 and 5.00 PM.Results are compared to moving flask values : in all the summer experiments photosynthesis was higher in the moving flask. Light variation effects (through water movements) on the water column photosynthetic budget are particularly notable at sunrise and sunset bouts : this budget may be over 2,5 times that of homogeneous nonturbulent water. During winter however, photosynthesis is higher for the stationary profile. We compared production recorded with the two systems, and calculated the mathematical relationship between the two systems over one day (exponential) and over the year (linear relationship).By extrapolation of the instant photosynthesis profile to a 24-hour period, we can evaluate the production gain with culture mixing. We calculated the net production for various days over the year; around the end of April, the mixed system became more productive than the stationary one.Considering our results in environmental conditions, it is obvious that they are not representative of all mixing systems, particularly the techniques in which algae cell position shift continually with respect to the photic zone : the positive effect of mixing in our ponds may be linked to the flashing light effect. In the literature, we can see that photosynthetic activity increases with flash time duration. Our production figures for various hours along the day (or various flash durations) are in agreement with these results.During low photosynthetic activity periods, the flashing light effect can not act since light is available at all depths of pond. The most important factor acting, in our experiments, seems to be light, since the two systems are in similar conditions.These results have clear implications for monitoring intensive outdoor algal cultures

Protein kinase C epsilon is required for macrophage activation and defense against bacterial infection

Imperial Cancer Research Fund, and grants FEDER 2FD-1997-1432 from Comisión Interministerial de Ciencia y Tecnología (CICYT) and PM98-0120 from Dirección General de Enseñanza Superior e Investigación Científica, Spain. F. Otto was supported by Deutsche Forschungsgemeinschaft grant Ot 134/1-1

Experimental functional response and inter-individual variation in foraging rate of teal (Anas crecca)

The functional response, i.e. the change in per capita food intake rate per time unit with changed food availability, is a widely used tool for understanding the ecology and behaviour of animals. However, waterfowl remain poorly explored in this context. In an aviary experiment we derived a functional response curve for teal (Anascrecca) foraging on rice (Oryzasativa) seeds. We found a linear relationship between intake rate and seed density, as expected for a filter-feeder. At high seed densities we found a threshold, above which intake rate still increased linearly but with a lower slope, possibly reflecting a switch from filter-feeding to a scooping foraging mode. The present study shows that food intake rate in teal is linearly related to food availability within the range of naturally occurring seed densities, a finding with major implications for management and conservation of wetland habitats.</p

Exploiting lipid and polymer nanocarriers to improve the anticancer sonodynamic activity of chlorophyll

Sonodynamic therapy is an emerging approach that uses low-intensity ultrasound to activate a sonosensitizer agent triggering its cytotoxicity for selective cancer cell killing. Several molecules have been proposed as sonosensitizer agents, but most of these, as chlorophyll, are strongly hydrophobic with a low selectivity towards cancer tissues. Nanocarriers can help to deliver more efficiently the sonosensitizer agents in the target tumor site, increasing at the same time their sonodynamic effect, since nanosystems act as cavitation nuclei. Herein, we propose the incorporation of unmodified plant-extracted chlorophyll into nanocarriers with different composition and structure (i.e., liposomes, solid lipid nanoparticles and poly(lactic-co-glycolic acid) nanoparticles) to obtain aqueous formulations of this natural pigment. The nanocarriers have been deeply characterized and then incubated with human prostatic cancer cells (PC-3) and spheroids (DU-145) to assess the influence of the different formulations on the chlorophyll sonodynamic effect. The highest sonodynamic cytotoxicity was obtained with chlorophyll loaded into poly(lactic-co-glycolic acid) nanoparticles, showing promising results for future clinical investigations on sonodynamic therapy

Average mass of seeds encountered by foraging dabbling ducks in Western Europe

Many dabbling ducks Anas spp. are largely granivorous, consuming a variety of seeds chiefly from aquatic plants. To assess the relative value and carrying capacity of wetlands for dabbling ducks, species-specific information about seed mass is needed, but it is still largely missing or scattered in the literature. By combining weights of seeds collected in the field with a literature review, we provide a reference table for seed mass of 200 western European plant taxa frequently encountered by foraging dabbling ducks. Seeds collected in the field were sampled in microhabitats and at depths at which ducks were observed to forage, and study sites represent wintering, staging as well as breeding areas within a flyway in western Europe. When combined with calorimetric data, the present reference table will aid managers and scientists in assessing the importance of seed food resources at different sites and during different parts of the annual cycle.</p

Cilastatin Attenuates Cisplatin-Induced Proximal Tubular Cell Damage

A major area in cancer therapy is the search for protective strategies against cisplatin-induced nephrotoxicity. We investigated the protective effect of cilastatin on cisplatininduced injury to renal proximal tubular cells. Cilastatin is a specific inhibitor of renal dehydrodipeptidase I (DHP-I), which prevents hydrolysis of imipenem and its accumulation in the proximal tubule. Primary cultures of proximal cells were treated with cisplatin (1–30 M) in the presence or absence of cilastatin (200 g/ml). Apoptosis and mitochondrial injury were assessed by different techniques. Cisplatin uptake and DNA binding were measured by inductively coupled plasma spectrometry. HeLa cells were used to control the effect of cilastatin on the tumoricidal activity of cisplatin. Cisplatin increased cell death, apoptotic-like morphology, caspase activation, and mitochondrial injury in proximal tubular cells in a dose- and time-dependent way. Concomitant treatment with cilastatin reduced cisplatin-induced changes. Cilastatin also reduced the DNA-bound platinum but did not modify cisplatin-dependent up-regulation of death receptors (Fas) or ligands (tumor necrosis factor , Fas ligand). In contrast, cilastatin did not show any effects on cisplatintreated HeLa cells. Renal DHP-I was virtually absent in HeLa cells. Cilastatin attenuates cisplatin-induced cell death in proximal tubular cells without reducing the cytotoxic activity of cisplatin in tumor cells. Our findings suggest that the affinity of cilastatin for renal dipeptidase makes this effect specific for proximal tubular cells and may be related to a reduction in intracellular drug accumulation. Therefore, cilastatin administration might represent a novel strategy in the prevention of cisplatin-induced acute renal injury