Mesoscale survey of western and northwestern Irish lakes--spatial and aestival patterns in trophic status and phytoplankton community structure.

Inland water bodies are considered as integrated parts of the landscape and the monitoring of water quality and aquatic resources need to be addressed on a regional basis for optimal assessment and management. In this study, a simple stratified sampling scheme was applied to a mesoscale survey of western and northwestern Irish lakes, which was carried out to identify, based on the distribution patterns of phytoplankton biomass, potential associations between lake trophic state and land cover attributes. Phytoplankton community analysis was also performed to determine whether taxa associations reflected meteorology-linked aestival succession or specific spatial distributions. The assessment was based on the typology of hydrogeomorphological and land cover attributes of river catchments through ArcGIS analysis. Sampling was carried out in 50 lakes and during a 15-week period in summer 2009. Results showed a general longitudinal gradient in the trophic status of the lakes sampled, with a greater frequency of mesotrophic lakes in the eastern part of the study area where land cover is dominated by agricultural surfaces. Significant relationships (p < 0.010) were found between chlorophyll-a concentration and the proportion of river catchment surface covered by agriculture land and wetlands, findings which might be considered further as proxies for developing an eutrophication risk index. Multivariate analysis of phytoplankton community data clustered the sampled lakes into three assemblages, with ordination along axis 1 being significantly correlated to time and temperature (p < 0.006). There was greater frequency of occurrence of diatoms in lakes from cluster III (Kruskal-Wallis, p < 0.05, H = 6.34, df = 2, n = 49), concomitant to lower chlorophyll-a concentrations, lake surface temperatures and Secchi depths, reflecting meteorological conditions dominated by precipitations. Those results support the potential of mesoscale surveys to assess water quality variables and detect environmental patterns at regional scales.

Comparative summer dynamics of surface cyanobacterial communities in two connected lakes from the west of Ireland.

The eutrophication of lakes is typically associated with high biomass proliferations of potentially toxic cyanobacteria. At a regional level, the sustainable management of water resources necessitates an approach that recognises the interconnectivity of multiple water systems within river catchments. This study examined the dynamics in summer diversity of planktonic cyanobacterial communities and microcystin toxin concentrations in two inter-connected lakes from the west of Ireland prone to nutrient enrichment. DGGE analysis of 16S rRNA gene amplicons of genotype-I cyanobacteria (typically spherical) showed changes in the communities of both Lough Corrib and Ballyquirke Lough throughout the summer, and identified cyanobacterial genotypes both unique and shared to both lakes. Microcystin concentrations, estimated via the protein phosphatase 2A inhibition assay, were greater in August than in July and June in both lakes. This was concomitant to the increased occurrence of Microcystis as evidenced by DGGE band excision and subsequent sequencing and BLAST analysis. RFLP analysis of PCR amplified mcy-A/E genes clustered together the August samples of both lakes, highlighting a potential change in microcystin producers across the two lakes. Finally, the multiple factor analysis of the combined environmental data set for the two lakes highlighted the expected pattern opposing greater water temperature and chlorophyll concentration against macronutrient concentrations, but also indicated a negative relationship between microcystin concentration and cyanobacterial diversity, possibly underlining allelopathic interactions. Despite some element of connectivity, the dissimilarity in the composition of the cyanobacterial assemblages and the timing of community change in the two lakes likely were a reflexion of niche differences determined by meteorologically-forced variation in physico-chemical parameters in the two water bodies.

Molecular cloning and expression of ferritin mRNA in heavy metal-poisoned Xenopus laevis cells.

In a search for genes transcriptionally regulated by metal ions, we have isolated a Xenopus laevis ferritin cDNA clone, XL2-17, from cadmium-poisoned XL2 cells. The large size of the corresponding ferritin mRNA (1.4 kb) is due to the presence of a 629-nucleotide 5'-untranslated region. The Xenopus ferritin sequence is highly isologous with other vertebrate ferritins. In particular, there is a complete sequence identity for the iron-responsive element (IRE) located in the 5'-untranslated region in both XL2-17 and Rana catesbeiana ferritin mRNAs. The position of this IRE is unusual since it is located 489 nucleotides from the 5' end of the ferritin mRNA. Our analysis of phylogenetic relationships among ferritins indicates that all amphibian ferritins thus far sequenced would be more closely related to the mammalian H-type ferritin than to the L-type. The level of ferritin mRNA in XL2 cells rises 10- to 15-fold following exposure of cells to cadmium or copper. This increase is due to both transcriptional and translational regulation. A 10-fold increase was also found at the protein level. These results suggest that ferritin may be a primary detoxification response to heavy metals in Xenopus cells.

Molecular cloning and expression of a metallothionein mRNA in Xenopus laevis.

Metallothioneins (MT) are expressed during early development in species of several groups. To understand MT function in developmental processes, we studied the MT system of Xenopus laevis, a model vertebrate species in experimental embryology. We first purified and sequenced the liver MT from copper-treated animals. This 62-amino-acid protein shares the main structural properties of known vertebrate MT, and is more closely related to avian than to fish or mammalian MT. Using this sequence, we designed oligonucleotide primers to amplify and isolate a MT clone from a XL2 cell line cDNA library. This 752-bp cDNA encodes a putative 62-amino-acid-long protein that is 100% identical with the sequenced MT. Zinc, cadmium, and copper ions are very efficient inducers of MT mRNA accumulation in Xenopus liver and cell lines.

Stimulatory role of glial cells on the differentiation of dissociated chick embryo encephalon cells.

Dissociated cells from chick embryo encephalon of 36 h of incubation have been cultivated on fibroblast, meningeal cell, or glial layers. Within the first 24 h of cultivation, cells adhered to the preformed layers more firmly than to plastic or collagen surfaces. After 48 h of cultivation, the brain cells cultured on meningeal cell or fibroblast layers behaved very similarly to those cells cultured on plastic surfaces. But when cultured on glial layers for 3 days, the brain cells differentiated into characteristic neuroblasts, as demonstrated by specific neuronal stainings. These results support the hypothesis of a stimulatory role of glial cells in neuronal differentiation. The possible causes of this stimulatory action are discussed.

Single chloride-permeable channels of large conductance in cultured cardiac cells of new-born rats.

Large conductance channels were observed in the membrane of cultured cardiac cells of newborn rats studied with the patch-clamp technique in cell-attached and inside-out configurations. These channels were observed in approximately equal to 4% of the patches. In the cell-attached configuration they exhibited outward rectification and partial inactivation. In the inside-out configuration no rectification occurred but inactivation was present, mainly during hyperpolarizations. Two channels with large single unit conductances (400-450 pS) and one with a smaller conductance (200-250 pS) were frequently observed in the same patch. The two large channels generally had different kinetics. Under steady-state conditions the opening probability of the faster channel appeared to be voltage-independent. The slower channel was activated by depolarization. In asymmetrical solutions the permeability ratios PNa/PCl were 0.03 and 0.24 for the larger and smaller channels, respectively; corresponding values for PBa/PCl were 0.04 and 0.09. It is proposed that in cardiac membranes the chloride permeability system is composed of widely dispersed microclusters forming grouped channels of different types and sizes.

[Immunofluorescent study of the distribution of adult neuro-specific antigens in the chick embryo (author's transl)]. / Etude par immunofluorescence de l'apparition d'antigènes neuro-spécifiques d'adulte chez l'embryon de poulet.

The adult neuro-specific antigens have been localized by immunofluorescence techniques in diencephalon and mesencephalon of chick embryo. This study has been made using fresh or fixed tissues from embryos 72, 48 or 36 h old. At 72 h of incubation the wall of diencephalon shows marked fluorescence; at 48 h of incubation the fluorescent cells are localized in an outer layer and an inner one. In the 48 h-old embryo the reaction is more distinct and intensive in fresh tissues than in fixed tissues. At 36 h of incubation no fluorescence has been detected either in fresh tissues or in fixed tissues.