Effects of nutrient availability and neighbours on shoot growth,resprouting and flowering of Erica multiflora

Abstract. To test if low soil fertility and competition limit the performance of Mediterranean shrubs, and if the effects of competition on plant performance were modified by soil fertility, we subjected shrubs of Erica multiflora to a factorial field experiment of fertilization and removal of neighbours around target plants. After 18 months of treatment, fertilization had stimulated the growth of pre-existent sprouts and biomass allocation to stems into new sprouts, but decreased the frequency of sprout flowering. Removal of neighbours increased the number and biomass of new sprouts, the probability of sprout flowering and the biomass of flowers. Fertilization slightly enhanced sprout recruitment and the probability of sprout flowering when neighbours were removed, but did not modify the other parameters of plant performance. According to our results, both low soil fertility and competition limited plant performance. Competition was slightly more intense in fertilized plants, but only in determining sprout and flowering bud stimulation.     

European map of alien plant invasions based on the quantitative assessment across habitats

Aim Recent studies using vegetation plots have demonstrated that habitat type is a good predictor of the level of plant invasion, expressed as the proportion of alien to all species. At local scale, habitat types explain the level of invasion much better than alien propagule pressure. Moreover, it has been shown that patterns of habitat invasion are consistent among European regions with contrasting climates, biogeography, history and socioeconomic background. Here we use these findings as a basis for mapping the level of plant invasion in Europe. Location European Union and some adjacent countries. Methods We used 52,480 vegetation plots from Catalonia (NE Spain), Czech Republic and Great Britain to quantify the levels of invasion by neophytes (alien plant species introduced after ad 1500) in 33 habitat types. Then we estimated the proportion of each of these habitat types in CORINE land‐cover classes and calculated the level of invasion for each class. We projected the levels of invasion on the CORINE land‐cover map of Europe, extrapolating Catalonian data to the Mediterranean bioregion, Czech data to the Continental bioregion, British data to the British Isles and combined Czech–British data to the Atlantic and Boreal bioregions. Results The highest levels of invasion were predicted for agricultural, urban and industrial land‐cover classes, low levels for natural and semi‐natural grasslands and most woodlands, and the lowest levels for sclerophyllous vegetation, heathlands and peatlands. The resulting map of the level of invasion reflected the distribution of these land‐cover classes across Europe. Main conclusions High level of invasion is predicted in lowland areas of the temperate zone of western and central Europe and low level in the boreal zone and mountain regions across the continent. Low level of invasion is also predicted in the Mediterranean region except its coastline, river corridors and areas with irrigated agricultural land.     

Landscape context modulates alien plant invasion in Mediterranean forest edges

Natural habitats in human-altered landscapes are especially vulnerable to biological invasions, especially in their edges. We aim to understand the influence of landscape and local characteristics on biological invasions by exploring the level of plant invasion and alien species traits in forest edges in highly urbanized landscapes. We identified all plant species in 73 paired plots in the edge and 50 m towards the interior of the forest. We explored the association between alien species richness and similarity in species composition between edge and interior plots with landscape and local variables, using generalized linear models and variance partitioning techniques. Then, we performed Fourth-corner analyses to explore the association between alien plant traits and local and landscape variables. In contrast to native species richness, alien species richness was more affected by the surrounding landscape than by the local characteristics of the edge. Road proximity was positively associated with alien species richness and proportion and was its most important correlate, whereas disturbance was negatively associated with native species richness and was its most influential factor. Alien plant traits were also primarily associated with landscape characteristics. For instance, species of Mediterranean origin and introduced for agriculture were associated with higher agriculture use in the landscape. Our findings suggest that risk analyses of habitat vulnerability to invasion must consider the landscape context in order to successfully predict highly invaded areas and identify potentially successful invaders.     

Predators induce egg retention in prey

To prevent predation on their eggs, prey often avoid patches occupied by predators. As a result, they need to delay oviposition until they reach predator-free patches. Because many species allocate energy to egg production in a continuous fashion, it is not clear what kind of mechanism prey use to delay oviposition. We used females of the phytoseiid mite Neoseiulus cucumeris to study these mechanisms. Females were placed in patches with pollen, a food source they use for egg production, and they were exposed to another phytoseiid mite, Iphiseius degenerans, which is an intraguild predator of N. cucumeris juveniles. We found that the oviposition of N. cucumeris females on patches with the predator was lower than on patches without the predator. Cues left by the intraguild predator were not sufficient to elicit such behaviour. Females of N. cucumeris reduced oviposition when exposed to the predator by retaining the egg inside their body, resulting in a lower developmental rate once these eggs were laid. Hence, females are capable of retaining eggs, but the development of these eggs continues inside the mother’s body. In this way, females gain some time to search for less risky oviposition sites.     

The CarD/CarG regulatory complex is required for the action of several members of the large set of Myxococcus xanthus extracytoplasmic function σ factors

Extracytoplasmic function (ECF) σ factors are critical players in signal transduction networks involved in bacterial response to environmental changes. The Myxococcus xanthus genome reveals ～45 putative ECF‐σ factors, but for the overwhelming majority, the specific signals or mechanisms for selective activation and regulation remain unknown. One well‐studied ECF‐σ, CarQ, binds to its anti‐σ, CarR, and is inactive in the dark but drives its own expression from promoter P_QRS on illumination. This requires the CarD/CarG complex, the integration host factor (IHF) and a specific CarD‐binding site upstream of P_QRS. Here, we show that DdvS, a previously uncharacterized ECF‐σ, activates its own expression in a CarD/CarG‐dependent manner but is inhibited when specifically bound to the N‐terminal zinc‐binding anti‐σ domain of its cognate anti‐σ, DdvA. Interestingly, we find that the autoregulatory action of 11 other ECF‐σ factors studied here depends totally or partially on CarD/CarG but not IHF. In silico analysis revealed possible CarD‐binding sites that may be involved in direct regulation by CarD/CarG of target promoter activity. CarD/CarG‐linked ECF‐σ regulation likely recurs in other myxobacteria with CarD/CarG orthologous pairs and could underlie, at least in part, the global regulatory effect of the complex on M. xanthus gene expression.     

Critical role of mitochondrial glutathione in the survival of hepatocytes during hypoxia

Hypoxia is known to stimulate reactive oxygen species (ROS) generation. Because reduced glutathione (GSH) is compartmentalized in cytosol and mitochondria, we examined the specific role of mitochondrial GSH (mGSH) in the survival of hepatocytes during hypoxia (5% O2). 5% O2 stimulated ROS in HepG2 cells and cultured rat hepatocytes. Mitochondrial complex I and II inhibitors prevented this effect, whereas inhibition of nitric oxide synthesis with Nomega-nitro-L-arginine methyl ester hydrochloride or the peroxynitrite scavenger uric acid did not. Depletion of GSH stores in both cytosol and mitochondria enhanced the susceptibility of HepG2 cells or primary rat hepatocytes to 5% O2 exposure. However, this sensitization was abrogated by preventing mitochondrial ROS generation by complex I and II inhibition. Moreover, selective mGSH depletion by (R,S)-3-hydroxy-4-pentenoate that spared cytosol GSH levels sensitized rat hepatocytes to hypoxia because of enhanced ROS generation. GSH restoration by GSH ethyl ester or by blocking mitochondrial electron flow at complex I and II rescued (R,S)-3-hydroxy-4-pentenoate-treated hepatocytes to hypoxia-induced cell death. Thus, mGSH controls the survival of hepatocytes during hypoxia through the regulation of mitochondrial generation of oxidative stress.     

Prevalence of the C282Y, H63D, and S65C mutations of the HFE gene in 1,146 newborns from a region of Northern Spain

In Spain, 85% of patients with genetic hemochromatosis (GH) are homozygous for the C282Y mutation of the HFE gene. H63D and S65C mutations of HFE may also play some role in the disease. The aim of this study was to establish the prevalence of C282Y, H63D, and S65C mutations of the HFE gene in newborns in Catalonia, Spain. One thousand one hundred forty-six newborn screening cards were selected randomly. DNA from these cards was extracted and HFE mutations were analyzed with the LightCycler equipment (Roche Diagnostics Gmbh, Mannheim, Germany). Sufficient DNA sample was obtained to screen for the three mutations in 1,043 cases (91%). The allelic frequencies of C282Y, H63D, and S65C mutations were 0.03 (IC 95% 0.022-0.037), 0.2 (IC 95% 0.19-0.22), and 0.01 (95% confidence interval [CI] 0.006-0.015), respectively. The frequency of C282Y homozygous newborns was 0.001 (95% CI 0.0005-0.0014). The frequencies of newborns doubly heterozygous for C282Y/H63D and C282Y/S65C were 0.01 (95% CI 0.005-0.02) and 0.002 (95% CI 0.0002-0.01), respectively. The allelic frequency of C282Y mutation is similar to that observed in Southern France, in the Czech Republic and in some areas of Italy. The allelic frequency of H63D mutation in Catalonia is the highest reported to date. Nevertheless, S65C is infrequent. These data should be kept in mind when designing hemochromatosis genotypic screening programs in Catalonia.     

Architecture of CRM1/Exportin1 suggests how cooperativity is achieved during formation of a nuclear export complex

CRM1/Exportin1 mediates the nuclear export of proteins bearing a leucine-rich nuclear export signal (NES) by forming a cooperative ternary complex with the NES-bearing substrate and the small GTPase Ran. We present a structural model of human CRM1 based on a combination of X-ray crystallography, homology modeling, and electron microscopy. The architecture of CRM1 resembles that of the import receptor transportin1, with 19 HEAT repeats and a large loop implicated in Ran binding. Residues critical for NES recognition are identified adjacent to the cysteine residue targeted by leptomycin B (LMB), a specific CRM1 inhibitor. We present evidence that a conformational change of the Ran binding loop accounts for the cooperativity of Ran- and substrate binding and for the selective enhancement of CRM1-mediated export by the cofactor RanBP3. Our findings indicate that a single architectural and mechanistic framework can explain the divergent effects of RanGTP on substrate binding by many import and export receptors.