Seasonal succession of phytoplankton in a lake of the Paraná river floodplain,Argentina

Phytoplankton biomass, morphological and taxonomic composition, species diversity and productivity were analyzed in a shallow lake of the Middle Paraná River floodplain (El Tigre, 31 ° 41 S and 60° 42 W), between November 1986 and July 1988. Lake inundation (filling and through-flow phases) constituted an intense long-term perturbation in the physical and chemical environment. As the lake filled with river water, K-selected species (netplanktonic filamentous bluegreens, > 37 µm, with low surface area/volume (SA/V) ratios) that had existed prior to filling (late spring 1986) were replaced in summer-fall by r-selected species (nannoplanktonic chlorophytes and cryptophytes, < 37 µm, mainly stout forms with high SA/V ratios). During the through-flow phase, lentic phytoplankton was replaced by lotic flagellate populations due to the direct flushing by river water. During the period of falling water (drainage and isolation phases), nanoplanktonic algae with similar characteristics to those of the filling phase dominated in late winter-spring. Later in the isolation phase, these were succeeded by K-selected species (netplanktonic algae, mainly motile spherical dinoflagellates and filamentous bluegreens with low SA/V ratios). Simultaneously, primary production per unit biomass decreased and total biomass and specific diversity increased. Seasonal changes of phytoplankton in floodplain lakes can be interpreted as the interaction between true successional development (as observed in the drainage and isolation phases) and intermediate disturbance. Using Reynolds' terminology, short-term disturbance (slight inflow of nutrient-rich river water) caused reversion to an earlier stage in the former succession, and long-term disturbance (lake inundation) truncated the successional progression and a new (or shifted) succession was initiated.     

Resistance to the cereal cyst nematode (Heterodera avenae Woll.) transferred from the wild grassAegilops ventricosa to hexaploid wheat by a “stepping-stone” procedure

Transfer of resistance toHeterodera avenae, the cereal cyst nematode (CCN), by a stepping-stone procedure from the wild grassAegilops ventricosa to hexaploid wheat has been demonstrated. The number of nematodes per plant was lower, and reached a plateau much earlier, in the resistant introgression line H93-8 (1–2 nematodes per plant) than in the recipient H10-15 wheat (14–16 nematodes per plant). Necrosis (hypersensitive reaction) near the nematode, little cell fusion, and few, often degraded syncytia were observed in infested H93-8 roots, while abundant, well-formed syncytia were present in the susceptible H10-15 wheat. Line H93-8 was highly resistant to the two Spanish populations tested, as well as the four French races (Fr1-Fr4), and the British pathotype Hall, but was susceptible to the Swedish pathotypes HgI and HgIII. Resistance was inherited as though determined by a single quasi-dominant factor in the F₂ generations resulting from crosses of H93-8 with H10-15 and with Loros, a resistant wheat carrying the geneCre1 (syn.Ccn1). The resistance gene in H93-8 (Cre2 orCcn2) is not allelic with respect to that in Loros. RFLPs and other markers, together with the cytogenetical evidence, indicate that theCre2 gene has been integrated into a wheat chromosome without affecting its meiotic pairing ability. Introduction ofCre2 by backcrossing into a commercial wheat backgroud increases grain yield when under challenge by the nematode and is not detrimental in the absence of infestation.     

Kinetic study of the cytotoxic effect of α-sarcin,a ribosome inactivating protein fromAspergillus giganteus,on tumour cell lines: protein biosynthesis inhibition and cell binding

-Sarcin is a ribosome inactivating protein produced by the mouldAspergillus giganteus. The effect of this protein on eight different tumour cell lines has been studied in the absence of any agent affecting membrane permeability. The protein is cytotoxic for all the tumour cell lines considered. -Sarcin modifies the cell proliferation pattern by inhibiting the protein biosynthesis of the cultured cells. No membrane damage produced by -sarcin has been observed by measuring lactic dehydrogenase leakage. Alteration on the cell mitochondrial activity has not been detected upon treatment with -sarcin. Differences on the extent of the protein binding to the cells have been observed by flow cytometric measurements. The kinetic analysis of the protein biosynthesis inhibition produced by -sarcin reveals an -sarcin concentration-dependent lag phase followed by a first order decrease of the protein synthesis rate. This parameter is dependent on the external -sarcin concentration. A saturable component for the action of -sarcin is also deduced from these experiments. Results are discussed in terms of the protein passage across the cell membrane as the potential rate-limiting step for the action of -sarcin.     

Erk1/2 signaling mediates the HGF-induced protection against ethanol and acetaldehyde-induced toxicity in the pancreatic RINm5F cell line

Alcohol-induced pancreas damage remains as one of the main risk factors for pancreatitis development. This disorder is poorly understood, particularly the effect of acetaldehyde, the primary alcohol metabolite, in the endocrine pancreas. Hepatocyte growth factor (HGF) is a protective protein in many tissues, displaying antioxidant, antiapoptotic, and proliferative responses. In the present work, we were focused on characterizing the response induced by HGF and its protective mechanism in the RINm5F pancreatic cell line treated with ethanol and acetaldehyde. RINm5F cells were treated with ethanol or acetaldehyde for 12 h in the presence or not of HGF (50 ng/ml). Cells under HGF treatment decreased the content of reactive oxygen species and lipid peroxidation induced by both toxics, improving cell viability. This effect was correlated to an improvement in insulin expression impaired by ethanol and acetaldehyde. Using a specific inhibitor of Erk1/2 abrogated the effects elicited by the growth factor. In conclusion, the work provides mechanistic evidence of the HGF-induced-protective response to the alcohol-induced damage in the main cellular component of the endocrine pancreas.     

Metabarcoding reveals seasonal and spatial patterns of arthropod community assemblages in two contrasting habitats: Desert and oasis of the Baja California Peninsula,Mexico

Aim

Desert springs or oases are the only permanent mesic environments in highly water-limited arid regions. Oases have immense cultural, evolutionary and ecological importance for people and a high number of endemic and relic species. Nevertheless, they are also highly vulnerable ecosystems, with invasive species, overexploitation and climate change being the primary threats. We used the arthropod communities' spatiotemporal diversity and distribution patterns as a proxy to understand biodiversity dynamics in two geographically close but ecologically contrasting and highly threatened ecosystems: deserts and oases.

Location

Baja California Peninsula, Mexico.

Methods

Arthropod communities at five oases and surrounding desert scrub areas were sampled in two seasons. Using DNA metabarcoding and traditional taxonomic surveys, we tried to identify what biotic and abiotic characteristics of the habitat are important drivers of arthropod diversity and how these characteristics can change across spatial and temporal scales.

Results

Over 6200 individuals representing 23 orders were collected. In oasis samples, the community composition fluctuated more in space (i.e. among sites) than in time (i.e. seasons). Thus, seasonal changes did not affect oasis community diversity and composition, but the dissimilarity among sites increased with geographic distance. Moreover, anthropic activities negatively correlated with arthropod diversity in oases. On the other hand, the season, geography (e.g. latitude) and biotic characteristics of the habitat (e.g. sampled scrub species) significantly affected the diversity and composition of the desert arthropod communities.

Main Conclusions

Neutral dynamics (e.g. historical climatic events, dispersal limitation and spatial component) and human impact significantly influenced the biodiversity patterns of each oasis. In contrast, the habitat's seasonal variation and biotic characteristics were the most important variables influencing the diversity of the desert communities. Baja California oases harbour distinct invertebrate communities; therefore, each oasis should be conserved individually to preserve these unique assemblages.     

Characterization of urease from the phototrophic bacteriumRhodobacter capsulatus E1F1

Rhodobacter capsulatus E1F1 showed high cytosolic urease activity when growing on urea, purines, and purine metabolites as nitrogen source. Molecular mass ofR. capsulatus enzyme is similar to that of other bacteria and greatly differs from that of jack bean. Kinetic parameters of partially purifiedR. capsulatus enzyme resemble those described in other bacterial ureases. The activity was inhibited by metal-chelating agents and by mercurials. Urease fromR. capsulatus E1F1 was negligible in nitrogen-starved cells or in cells cultured with nitrate, ammonium, or amino acids. Moreover, ammonium inhibited both the urea uptake and the urease activity expression inR. capsulatus cells.     

Towards an ethical and legal framework in archeogenomics: A local case in the Atlantic coast of central Patagonia

Ethical discussions around ancient DNA (aDNA) research predate the technological breakthroughs that led to the accelerated generation of ancient genomic data, revealing a long-due need to address these aspects in the field. Given the diverse conflicts that genomics has raised towards the communities associated with the Non-living Human Ancestors under study, it has been suggested that the ethical and legal implications of genetically studying present-day and ancient human populations should be considered case-by-case. Nevertheless, the discussions have focused on US and European perspectives. To contribute from a local and Latin American position to the problem, we present the history of consensus and disagreement of the relationships between scientists and Indigenous communities of the Atlantic coast of the central Argentinian Patagonia. We describe how these relationships resulted in the approval of a groundbreaking provincial law that acknowledges the Indigenous community's right to be involved in decision-making concerning their Ancestors. In addition, we emphasize how these established relationships allowed the development of aDNA studies. With this background, we address the main ethical concerns of genomic studies of Ancestors identified in the reference literature and commit to applying some of the recommendations suggested in those ethical guidelines. Then, we reflect on possible negative consequences of ongoing research and propose some suggestions based on personal experiences that will contribute to moving the ethical field towards a more contextualized science with a local perspective.     

Identification of a novel mechanism for LFA-1 organization during NK cytolytic response

The elimination of transformed and viral infected cells by natural killer (NK) cells requires a specialized junction between NK and target cells, denominated immunological synapse (IS). After initial recognition, the IS enables the directed secretion of lytic granules content into the susceptible target cell. The lymphocyte function-associated antigen (LFA)-1 regulates NK effector function by enabling NK-IS assembly and maturation. The pathways underlying LFA-1 accumulation at the IS in NK cells remained uncharacterized. A kinase anchoring protein 350 (AKAP350) is a centrosome/Golgi-associated protein, which, in T cells, participates in LFA-1 activation by mechanisms that have not been elucidated. We first evaluated AKAP350 participation in NK cytolytic activity. Our results showed that the decrease in AKAP350 levels by RNA interference (AKAP350KD) inhibited NK-YTS cytolytic activity, without affecting conjugate formation. The impairment of NK effector function in AKAP350KD cells correlated with decreased LFA-1 clustering and defective IS maturation. AKAP350KD cells that were exclusively activated via LFA-1 showed impaired LFA-1 organization and deficient lytic granule translocation as well. In NK AKAP350KD cells, activation signaling through Vav1 was preserved up to 10 min of interaction with target cells, but significantly decreased afterwards. Experiments in YTS and in ex vivo NK cells identified an intracellular pool of LFA-1, which partially associated with the Golgi apparatus and, upon NK activation, redistributed to the IS in an AKAP350-dependent manner. The analysis of Golgi organization indicated that the decrease in AKAP350 expression led to the disruption of the Golgi integrity in NK cells. Alteration of Golgi function by BFA treatment or AKAP350 delocalization from this organelle also led to impaired LFA-1 localization at the IS. Therefore, this study characterizes AKAP350 participation in the modulation of NK effector function, revealing the existence of a Golgi-dependent trafficking pathway for LFA-1, which is relevant for LFA-1 organization at NK-lytic IS.