Euplotes Cytoskeleton: Tubulin and Microtubular Systems in Interphase1,2

The Euplotes cytoskeleton obtained by treatment with Triton X-100 in a microtubule-stabilizing buffer has been studied by electron microscopy and SDS-polyacrylamide electrophoresis. An antiserum has been prepared using the tubulin band from preparative gels of Euplotes cytoskeletons as an antigen. This antiserum reacts with the tubulin from different ciliated protozoa but fails to recognize the vertebrate tubulin by immunoblotting. Immunoblotting studies have demonstrated a slower electrophoretic mobility for the α-tubulin of Euplotes and Oxytricha than that of Paramecium and Tetrahymena. A cytoplasmic microtubular network in Euplotes has been revealed by indirect immunoftuorescence using both an anti-α-tubulin monoclonal antibody directed against chick brain tubulin and an antiserum raised against the tubulin of Euplotes.     

Phagocytic Activity of Three Naegleria Strains in the Presence of Erythrocytes of Various Types1

The phagocytic activities of N. lovaniensis (Aq/9/1/45D) and N. gruberi (1518/1f and 1518/1e) were studied in the presence of erythrocytes of various species: chicken, rabbit, goat, and human (A⁺, B⁺, and AB⁺ were tested). The percentage of amoebae with ingested red cells, the phagocytic index (PhI), can be considered as an expression of phagocytic activity. Under given conditions (erythrocyte concentration, incubation time, age of amoebic cultures) each strain of Naegleria prefers one erythrocyte type. Thus, for 72-h cultures, N. lovaniensis ingested more A⁺ type erythrocytes than did N. gruberi strains but had very low affinity for rabbit red cells except when very high concentrations were tested. Naegleria gruberi 1f was the most active of the three strains towards rabbit and B⁺ and AB⁺ human erythrocytes, but very low PhIs were obtained with goat erythrocytes. Naegleria gruberi le exhibited high phagocytic activity for every erythrocyte type except for rabbit red cells.     

The K+/H+ antiporter LeNHX2 increases salt tolerance by improving K+ homeostasis in transgenic tomato

The endosomal LeNHX2 ion transporter exchanges H⁺ with K⁺ and, to lesser extent, Na⁺. Here, we investigated the response to NaCl supply and K⁺ deprivation in transgenic tomato (Solanum lycopersicum L.) overexpressing LeNHX2 and show that transformed tomato plants grew better in saline conditions than untransformed controls, whereas in the absence of K⁺ the opposite was found. Analysis of mineral composition showed a higher K⁺ content in roots, shoots and xylem sap of transgenic plants and no differences in Na⁺ content between transgenic and untransformed plants grown either in the presence or the absence of 120 mm NaCl. Transgenic plants showed higher Na⁺/H⁺ and, above all, K⁺/H⁺ transport activity in root intracellular membrane vesicles. Under K⁺ limiting conditions, transgenic plants enhanced root expression of the high‐affinity K⁺ uptake system HAK5 compared to untransformed controls. Furthermore, tomato overexpressing LeNHX2 showed twofold higher K⁺ depletion rates and half cytosolic K⁺ activity than untransformed controls. Under NaCl stress, transgenic plants showed higher uptake velocity for K⁺ and lower cytosolic K⁺ activity than untransformed plants. These results indicate the fundamental role of K⁺ homeostasis in the better performance of LeNHX2 overexpressing tomato under NaCl stress.     

Ligands of boron in Pisum sativum nodules are involved in regulation of oxygen concentration and rhizobial infection

Boron (B) is an essential nutrient for N₂‐fixing legume–rhizobia symbioses, and the capacity of borate ions to bind and stabilize biomolecules is the basis of any B function. We used a borate‐binding‐specific resin and immunostaining techniques to identify B ligands important for the development of Pisum sativum–Rhizobium leguminosarum 3841 symbiotic nodules. arabinogalactan–extensin (AGPE), recognized by MAC 265 antibody, appeared heavily bound to the resin in extracts derived from B‐sufficient, but not from B‐deficient nodules. MAC 265 stained the infection threads and the extracellular matrix of cortical cells involved in the oxygen diffusion barrier. In B‐deprived nodules, immunolocalization of MAC 265 antigens was significantly reduced. Leghaemoglobin (Lb) concentration largely decreased in B‐deficient nodules. The absence of MAC 203 antigens in B‐deficient nodules suggests a high internal oxygen concentration, as this antibody detects an epitope on the lipopolysaccharide (LPS) of bacteroids typically expressed in micro‐aerobically grown R. leguminosarum 3841. However, B‐deprived nodules did not accumulate oxidized lipids and proteins, and revealed a decrease in the activity of the major antioxidant enzyme ascorbate peroxidase (APX). Therefore, B deficiency reduced the stability of nodule macromolecules important for rhizobial infection, and for regulation of oxygen concentration, resulting in non‐functional nodules, but did not appear to induce oxidative damage in low‐B nodules.     

Performance and fate of tree seedlings on and around nests of the leaf‐cutting ant Atta cephalotes: Ecological filters in a fragmented forest

Habitat fragmentation is currently the most pervasive anthropogenic disturbance in tropical forests and some species of leaf‐cutting ants of the genus Atta (dominant herbivores in the neotropics) have become hyper‐abundant in forest edges where their nests directly impact up to 6% of the forest area. Yet, their impacts on the regeneration dynamics of fragmented forests remain poorly investigated. Here we examine the potential of Atta cephalotes nests to function as ecological filters impacting tree recruitment. Growth, survival and biomass partitioning of experimentally planted seedlings (six tree species) were examined at eight spatially independent A. cephalotes colonies in a large Atlantic Forest fragment. Seedling performance and fate (leaf numbers and damage) were monitored up to 27 months across three habitats (nest centre, nest edge and forest understorey). Plants at illuminated nest centres showed twice the gross leaf gain as understorey individuals. Simultaneously, seedlings of all species lost many more leaves at nests than in the forest understorey, causing a negative net leaf gain. Net leaf gain in the shaded understorey ranged from zero (Licania and Thyrsodium species) to substantial growth for Copaifera and Virola, and intermediate levels little above zero for Protium and Pouteria. Also seedling survival differed across habitats and species, being typically low in the centre and at the edge of nests where seedlings were often completely defoliated by the ants. Lastly, seedling survival increased strongly with seed size at nest edges while there was no such correlation in the forest. Our results suggest that Atta nests operate as ecological filters by creating a specific disturbance regime that differs from other disturbances in tropical forests. Apparently, Atta nests favour large‐seeded tree species with resprouting abilities and the potential to profit from a moderate, nest‐mediated increase in light availability.     

Do abandoned nests of leaf‐cutting ants enhance plant recruitment in the Atlantic Forest?

The role played by abandoned nests of leaf‐cutting ants (Atta spp.) as a small‐scale disturbance regime that affects plant recruitment, species coexistence and forest regeneration remains poorly investigated. Here we examine whether abandoned nests of Atta cephalotes serve as regeneration niches and operate as particular plant recruitment habitats, favouring forest regeneration after ant activities cease and leading to the establishment of taxonomically/ecologically distinct plant assemblages. Soil properties, canopy openness, light availability and regenerating plant assemblages were evaluated across 18 nests and adjacent control plots in a large remnant of Atlantic Forest in north‐east Brazil from December 2004 to December 2005. Surprisingly, nests and control plots exhibited very similar light environments irrespective of nest age, but nest soils exhibited substantial reductions in carbon content (1.45 ± 0.24 vs. 1.79 ± 0.13%) and organic matter (2.50 ± 0.41 vs. 3.08 ± 0.23%), and proved to be much more resistant to penetration (30.57 ± 6.08 vs. 39.48 ± 7.53 mm). Functional signature of regenerating plant assemblages exhibited little variation across both habitat types, as they were dominated by pioneer, small‐seeded and vertebrate‐dispersed species. However, abandoned nests exhibited less dense, impoverished and more homogeneous regenerating plant assemblages at local and landscape scale; they clearly lacked nest‐dependent plant species and represented floristic subsets of the flora inhabiting the undisturbed forest. This recruitment bottleneck was transient in the long term because nest‐related effects ameliorated in older nests. Our results suggest that, unlike treefall gaps, abandoned nests represent temporary (relatively long‐lasting) islands of unsuitable substrate that reduce plant recruitment, retard forest regeneration, and fail in providing a special regeneration niche able to promote species coexistence and plant diversity.     

Life history variation between species of the relictual genus Borderea (Dioscoreaceae): phylogeography, genetic diversity, and population genetic structure assessed by RAPD markers

The genus Borderea consists of two species, B. pyrenaica and B. chouardii, taxa which have been previously considered as conspecific due to their overall close morphology. These two sole species of the rare genus of Dioscoreaceae are endemic to the Pyrenees (Spain, France). This mountain range likely operated as a refugium for these plants during the last glaciations. B. chouardii is only known from a single population in the Spanish Prepyrenees and has been classified as at risk of extinction in the Red List of Endangered Species (IUCN); B. pyrenaica shows a narrow distribution range in the central Pyrenees and Prepyrenees. We analysed genetic variation, population structure and differentiation in these two taxa using RAPD markers. Our study was conducted on the same seven populations for which very low levels of genetic differentiation were detected previously through allozyme analysis. By contrast, high levels of genetic variability were detected through the RAPD hypervariable markers. Twelve RAPD primers produced 112 distinct bands in the 397 surveyed individuals, totalling 395 different RAPD phenotypes. Only four bands were monomorphic across all samples of Borderea, whereas 21 of the polymorphic bands were species‐specific (20 for B. chouardii, and one for B. pyrenaica). The largest genetic distances were those between the B. chouardii and the B. pyrenaica phenotypes. An analysis of molecular variance showed greater variance between groups (B. chouardii vs. B. pyrenaica, 76.08%) than within groups (3.60%). RAPD band specificity, phenotypic distances, and the partitioning of variance all support the taxonomic separation of the two species. Statistical evaluation of within‐ and among‐population RAPD genetic variability in B. pyrenaica showed that genetic variability was higher within populations (>80%) than among them. No clear pattern of RAPD differentiation could be observed among the six studied populations of this taxon though slight differences in genetic diversity could be observed in the more isolated Prepyrenean populations compared with the more widespread Pyrenean ones. These results suggest a recent postglacial origin of the present B. pyrenaica populations. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80 , 483–498.     

Remote sensing of riverine landscapes

1. The fashion for examining riverine landscapes is changing as our technical instruments, from microprobes to satellites, expands to be able to examine the spatial and temporal relationships among biota, hydrology and geomorphology across scales from microhabitats to channel units to valleys to catchments. 2. The range of successful applications from remote sensing analyses of riverine landscapes has especially increased with the launch of many new instruments that record data across the electromagnetic spectrum. Engineering of the instruments has also improved such that knowledge of the radiometric properties of the digital data is more complete as a result of better instrumentation and installation of on‐board calibrations systems for many instruments. 3. With the development of faster processing on cheaper computers, it is now common for comprehensive data sets to be processed through algorithms that previously could only be applied to relatively small (<1 Mbyte) rasters of data. This technical advance is especially important for the statistical algorithms such as principal components and spectral mixture analysis that can decompose gradients in the spectral data. The combined effect is the production of regional views of riverine landscapes separated into components of water, vegetation and soil. 4. The landscape properties of riverine landscapes that have been most successfully measured with remote sensing data include community and habitat level classification and connectivity of waterbodies with optical and radar data. Laser and radar altimetric data measured from aircraft provide land elevations at resolutions as fine as decimetres. A remaining challenge is to achieve an exact match between the categories of landscape classification from the remote sensing analysis and data from field surveys or model outputs. 5. In contrast to many landscape properties, several water properties are now routinely measured as absolute values (water surface elevation, temperature, surface sediment concentration and algal concentration) with remote sensing. New analyses of both passive and active radar data in addition have led to measurements of inundation and wetness that are providing valuable insight into the dynamics of flooding and its effect on riverine landscapes. 6. Finally, an effective examination of the variability in landscape cover includes additional analyses of remote sensing products using pattern metrics that measure the scale of patchiness and distribution of the landscape properties. These types of variability measures at the regional scale contribute to an increased understanding of the way in which spatial heterogeneity of riverine landscapes varies across scales and how landscape filters (sensu Poff, 1997) influence the evolution of these diversity patterns.     

Bottled Mineral Waters Polluted by Protozoa in Mexico

A survey of protozoa polluting bottled mineral water in Mexico was carried out using samples obtained from the three best-selling brands of bottled mineral water in the country. The organisms were concentrated through filtration procedures and subsequently cultured in sterile media. The cultures were observed over four weeks, with identification to the level of genus and species. Most commonly found were the amoebae Naegleria gruberi, Acanthamoeba astronyxis, and Vahlkampfia vahlkampfi (trophic as well as cystic stages) plus one flagellate, Bodomorpha minima. No ciliates were detected. The public health importance of the findings is obvious, since some strains of Naegleria and Acanthamoeba have the potential to cause human disease that may lead to death.