Contrasting historical and current land-use correlation with diverse components of current alien plant invasions in Mediterranean habitats

Habitat invasion by alien plants is strongly modulated by environmental and landscape factors. However, the effect of landscape history remains largely unknown, despite the fact that it could play an important role in many stages of invasion processes, even long after land-use changes have occurred determining invasion debts. We analysed the effects of past landscape and recent changes therein, together with habitat type and current context (i.e. climate, topography and landscape), on three components of the invasion process at habitat scale: alien species presence (i.e. at least one alien species occurring), richness (number of species found) and abundance (mean species cover). We selected 531 plots in nine habitat types in Barcelona province (7725 km²) and recorded alien (neophyte) species cover. We performed Generalized Linear Models on these invasion components using the generated data and a set of predictors of habitat, context and landscape factors obtained from plot sampling and digital cartography. The results show that invasion components are affected by diverse habitat and context factors and, in some cases, by landscape history. Alien species presence is influenced by habitat type and the current environmental context, and by the number of habitat changes in the adjacent landscape; on the other hand, species richness is only associated with the current context and species abundance is only influenced by historical cropland cover. The association between alien species presence and abundance and past and recent landscape changes suggests the existence of accumulated invasion debts at habitat scale that might be relevant to habitat management.     

Radioluminescence Microscopy: Measuring the Heterogeneous Uptake of Radiotracers in Single Living Cells

Radiotracers play an important role in interrogating molecular processes both in vitro and in vivo. However, current methods are limited to measuring average radiotracer uptake in large cell populations and, as a result, lack the ability to quantify cell-to-cell variations. Here we apply a new technique, termed radioluminescence microscopy, to visualize radiotracer uptake in single living cells, in a standard fluorescence microscopy environment. In this technique, live cells are cultured sparsely on a thin scintillator plate and incubated with a radiotracer. Light produced following beta decay is measured using a highly sensitive microscope. Radioluminescence microscopy revealed strong heterogeneity in the uptake of [¹⁸F]fluoro-deoxyglucose (FDG) in single cells, which was found consistent with fluorescence imaging of a glucose analog. We also verified that dynamic uptake of FDG in single cells followed the standard two-tissue compartmental model. Last, we transfected cells with a fusion PET/fluorescence reporter gene and found that uptake of FHBG (a PET radiotracer for transgene expression) coincided with expression of the fluorescent protein. Together, these results indicate that radioluminescence microscopy can visualize radiotracer uptake with single-cell resolution, which may find a use in the precise characterization of radiotracers.     

Light on the structural communication in Ras GTPases

The graph theory was combined with fluctuation dynamics to investigate the structural communication in four small G proteins, Arf1, H-Ras, RhoA, and Sec4. The topology of small GTPases is such that it requires the presence of the nucleotide to acquire a persistent structural network. The majority of communication paths involves the nucleotide and does not exist in the unbound forms. The latter are almost devoid of high-frequency paths. Thus, small Ras GTPases acquire the ability to transfer signals in the presence of nucleotide, suggesting that it modifies the intrinsic dynamics of the protein through the establishment of regions of hyperlinked nodes with high occurrence of correlated motions. The analysis of communication paths in the inactive (S^GDP) and active (S^GTP) states of the four G proteins strengthened the separation of the Ras-like domain into two dynamically distinct lobes, i.e. lobes 1 and 2, representing, respectively, the N-terminal and C-terminal halves of the domain. In the framework of this separation, interfunctional states and interfamily differences could be inferred. The structure network undergoes a reshaping depending on the bound nucleotide. Nucleotide-dependent divergences in structural communication reach the maximum in Arf1 and the minimum in RhoA. In Arf1, the nucleotide-dependent paths essentially express a communication between the G box 4 (G4) and distal portions of lobe 1. In the S^GDP state, the G4 communicates with the N-term, while, in the S^GTP state, the G4 communicates with the switch II. Clear differences could be also found between Arf1 and the other three G proteins. In Arf1, the nucleotide tends to communicate with distal portions of lobe 1, whereas in H-Ras, RhoA, and Sec4 it tends to communicate with a cluster of aromatic/hydrophobic amino acids in lobe 2. These differences may be linked, at least in part, to the divergent membrane anchoring modes that would involve the N-term for the Arf family and the C-term for the Rab/Ras/Rho families.     

Trichoderma asperellum Strain T34 Controls Fusarium Wilt Disease in Tomato Plants in Soilless Culture Through Competition for Iron

Trichoderma asperellum strain T34 has been reported to control the disease caused by Fusarium oxysporum f.sp. lycopersici (Fol) on tomato plants. To study the importance of iron concentration in the growth media for the activity and competitiveness of T34 and the pathogen, we tested four iron concentrations in the nutrient solution [1, 10, 100, and 1000 μM provided as EDTA/Fe(III)] in a biological control experiment with T34 and Fol in tomato plants. The reduction of the Fusarium-infected shoot by T34 was only significant at 10 μM Fe. We hypothesized that Fe competition is one of the key factors in the biocontrol activity exerted by T34 against Fol, as an increase in Fe concentration over 10 μM would lead to the suppression of T34 siderophore synthesis and thus inhibition of Fe competition with Fol. T34 significantly reduced the populations of Fol at all the doses of Fe assayed. In contrast, Fol enhanced the populations of T34 at 1 and 10 μM Fe. Nevertheless, several plant physiological parameters like net CO₂ assimilation (A), stomatal conductance (g _s), relative quantum efficiency of PSII (Φ _PSII), and efficiency of excitation energy capture by open PSII reactive centers (Fv′/Fm′) demonstrated the protection against Fol damage by treatment with T34 at 100 μM Fe. The first physiological parameter affected by the disease progression was g _s. Plant dry weight was decreased by Fe toxicity at 100 and 1,000 μM. T34-treated plants had significantly greater heights and dry weights than control plants at 1,000 μM Fe, even though T34 did not reduce the Fe content in leaves or stems. Furthermore, T34 enhanced plant height even at the optimal Fe concentration (10 μM) compared to control plants. In conclusion, T. asperellum strain T34 protected tomato plants from both biotic (Fusarium wilt disease) and abiotic stress [Fe(III) toxic effects].     

Thyroid hormone receptor expression in the obligatory paedomorphic salamander Necturus maculosus

Amphibian metamorphosis is under the strict control of thyroid hormones (TH). These hormones induce metamorphosis by controlling gene expression through binding to thyroid hormone receptors (TRs). Necturus maculosus is considered to be an obligatory paedomorphic Amphibian since metamorphosis never occurs spontaneously and cannot be induced by pharmacological means. Since metamorphosis depends on the acquisition of response of tadpole tissues to thyroid hormone, we aimed to determine TR gene expression patterns in Necturus maculosus as well as the expression of two TH-related genes: Cytosolic Thyroid Hormone-Binding Protein (CTHBP)-M2-pyruvate kinase, a gene encoding a cytosolic TH binding protein and stromelysin 3, a direct TH target gene in Xenopus laevis. Tissue samples were obtained from specimens of Necturus maculosus. We performed in situ hybridization using non-cross-hybridizing RNA probes obtained from the cloned Necturus TRalpha and TRbeta genes. We found clear expression of Necturus TRalpha gene in several tissues including the central nervous system, epithelial cells of digestive and urinary organs, as well as myocardium and skeletal muscle. TRbeta was also expressed in the brain. In other tissues, hybridization signals were too low to draw reliable conclusions about their precise distribution. In addition, we observed that the expression of CTHBP and ST3 is largely distinct from that of TRs. The fact that we observed a clear expression of TRalpha and TRbeta which are evolutionary conserved, suggests that Necturus tissues express TRs. Our results thus indicate that, in contrast to previously held hypotheses, Necturus tissues are TH responsive.     

Simultaneous quantitative LC-ESI-MS/MS analyses of salicylic acid and jasmonic acid in crude extracts of Cucumis sativus under biotic stress

Salicylic acid (SA) and jasmonic acid (JA) are plant hormones involved in basal resistance against plant pathogens and also in induced resistance. The aim of this study is to develop a fast and sensitive method to determine simultaneously the levels of both these hormones. The present paper proposes a method that includes hormone extraction with MeOH-H(2)O-HOAc (90:9:1, v/v), evaporation of the extracts, and injection into the liquid chromatography-electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) system in multiple reaction monitoring (MRM). Endogenous SA and JA levels in noninfested control cucumber cotyledons were 30.96 and 0.73ngg(-1) fresh weight, respectively. In roots, the levels were 8.31 and 15.82ngg(-1) FW, respectively. In plants treated with the biological control agent Trichoderma asperellum strain T-34, the levels of SA and JA did not differ from control plants. Rhizoctonia solani-diseased cucumber plants showed higher levels of SA and JA compared to noninfested controls (up to 2 and 13-fold higher, respectively). Detection limits for SA and JA were 0.45 and 0.47ngg(-1) fresh weight, respectively. The results of our research include the development of a method that is both fast and highly sensitive in the simultaneous quantitation of SA and JA from crude cucumber plant extracts, avoiding any purification and derivatization steps.