Phytosociological study of the Pinus occidentalis forests in the Dominican Republic

Abstract

The article deals both with the Pinus occidentalis pine tree forests growing on high mountain limestones and siliceous substrates, and with the copses growing on serpentines in Dajabón (Cibao Valley), Dominican Republic. The samplings carried out in these forests reveal the occurrence of numerous endemic species and, consequently, the habitats can be considered as endemic, priority habitats of the Antilles. The article relies on some previous surveys carried out by us, Cano E, Velóz Ramirez A, Cano-Ortiz A, Esteban FJ. (2009b). Analysis of the Pterocarpus officinalis forests in the Gran Estero (Dominican Republic). Acta Botanica Gallica 156(4):559–570, that made use of the data provided by 87 weather stations of the Dominican Republic. With the values of the Ci, Oi, Cti, etc. indexes, we make a bioclimatical proposal for Hispaniola. Our preliminary analysis of the studies published on the vegetation of the Island of Hispaniola and nearby islands, along with the samples taken by us, lead us to propose two new alliances: Ilici tuerckheimi–Pinion occidentalis and Phyllario mummularioidi–Leptogonion buchi, and three new associations: Dendropemon phycnophylli–Pinetum occidentalis, Cocotrino scopari–Pinetum occidentalis and Leptogono buchi–Pinetum occidentalis.     

Electron transport chain of Saccharomyces cerevisiae mitochondria is inhibited by H2O2 at succinate-cytochrome c oxidoreductase level without lipid peroxidation involvement

The deleterious effects of H₂O₂ on the electron transport chain of yeast mitochondria and on mitochondrial lipid peroxidation were evaluated. Exposure to H₂O₂ resulted in inhibition of the oxygen consumption in the uncoupled and phosphorylating states to 69% and 65%, respectively. The effect of H₂O₂ on the respiratory rate was associated with an inhibition of succinate-ubiquinone and succinate-DCIP oxidoreductase activities. Inhibitory effect of H₂O₂ on respiratory complexes was almost completely recovered by β-mercaptoethanol treatment. H₂O₂ treatment resulted in full resistance to Q_O site inhibitor myxothiazol and thus it is suggested that the quinol oxidase site (Q_O) of complex III is the target for H₂O₂. H₂O₂ did not modify basal levels of lipid peroxidation in yeast mitochondria. However, H₂O₂ addition to rat brain and liver mitochondria induced an increase in lipid peroxidation. These results are discussed in terms of the known physiological differences between mammalian and yeast mitochondria.     

Mechanism of FMN Binding to the Apoflavodoxin from Helicobacter pylori

Flavodoxins are bacterial electron transport proteins whose redox competence is due to the presence of a tightly but noncovalently bound FMN molecule. While the thermodynamics of the complex are understood, the mechanism of association between the apoflavodoxin and the redox cofactor is not so clear. We investigate here the mechanism of FMN binding to the apoflavodoxin from Helicobacter pylori, an essential protein that is being used as a target to develop antimicrobials. This flavodoxin is structurally peculiar as it lacks the typical bulky residue interacting with the FMN re face but bears instead a small alanine. FMN binding is biphasic, regardless of the presence of phosphate molecules in solution, while riboflavin binding takes place in a single step, the rate constant of which coincides with the fast phase of FMN binding. A mutational study at the isoalloxazine and phosphate subsites for FMN binding clearly indicates that FMN association is always limited by interaction with the isoalloxazine subsite because mutating residues that interact with the phosphate moiety of FMN in the native complex hardly changes the observed rate constants and amplitudes. In contrast, replacing tyr92, which interacts with the isoalloxazine, greatly lowers the rate constants. Our analysis indicates that the two FMN binding phases observed are related neither with alternative or sequential interaction with the two binding subsites nor with the presence of bound phosphate. It is possible that they reflect the intrinsic conformational heterogeneity of the apoflavodoxin ensemble.     

The isolated major homology region of the HIV capsid protein is mainly unfolded in solution and binds to the intact protein

Assembly of the mature human immunodeficiency virus type 1 (HIV-1) capsid involves the oligomerization of the capsid protein, CA. During retroviral maturation, the CA protein undergoes structural changes and forms exclusive intermolecular interfaces in the mature capsid shell, different from those in the immature precursor. The most conserved region of CA, the major homology region (MHR), is located in the C-terminal domain of CA (CTD). The MHR is involved in both immature and mature virus assembly; however, its exact function during both assembly stages is unknown. To test its conformational preferences and to provide clues on its role during CA assembly, we have used a minimalist approach by designing a peptide comprising the whole MHR (MHRpep, residues Asp152 to Ala174). Isolated MHRpep is mainly unfolded in aqueous solution, with residual structure at its C terminus. MHRpep binds to monomeric CTD with an affinity of ~30μM (as shown by fluorescence and ITC); the CTD binding region comprises residues belonging to α-helices 10 and 11. In the immature virus capsid, the MHR and α-helix 11 regions of two CTD dimers also interact [Briggs JAG, Riches JD, Glass B, Baratonova V, Zanetti G and Kr?usslich H-G (2009) Proc. Natl. Acad. Sci. USA 106, 11090-11095]. These results can be considered a proof-of-concept that the conformational preferences and binding features of isolated peptides derived from virus proteins could be used to mimic early stages of virus assembly.     

The molecular basis for antimicrobial activity of pore-forming cyclic peptides

The mechanism of action of antimicrobial peptides is, to our knowledge, still poorly understood. To probe the biophysical characteristics that confer activity, we present here a molecular-dynamics and biophysical study of a cyclic antimicrobial peptide and its inactive linear analog. In the simulations, the cyclic peptide caused large perturbations in the bilayer and cooperatively opened a disordered toroidal pore, 1–2 nm in diameter. Electrophysiology measurements confirm discrete poration events of comparable size. We also show that lysine residues aligning parallel to each other in the cyclic but not linear peptide are crucial for function. By employing dual-color fluorescence burst analysis, we show that both peptides are able to fuse/aggregate liposomes but only the cyclic peptide is able to porate them. The results provide detailed insight on the molecular basis of activity of cyclic antimicrobial peptides.     

A partial hominoid humerus from the middle miocene of Castell de Barberà (Vallès-Penedès Basin, Catalonia, Spain)

The hominoid right partial humerus IPS4334, from the middle Miocene (MN 8) of Castell de Barberà (Vallès-Penedès Basin, Catalonia, Spain), is described. It preserves the mid-distal portion of the shaft until the proximal margins of the radial and coronoid fossae, as well as the proximal portion of the olecranon fossa; the capitulum, the trochlea and the two epicondyles are missing. Although morphological comparisons are restricted, available evidence indicates that IPS4334 is more derived towards the modern hominoid condition than the Klein Hadersdorf specimen attributed to Griphopithecus (ca. 13-14 Ma), thus being most similar (except for its larger size and greater robusticity) to the presumably juvenile specimen of Dryopithecus fontani from Saint Gaudens in France (ca. 11-12 Ma). On the basis of shaft measurements and allometric regressions derived for extant hominoids, a body mass estimate around 50 kg is derived for IPS4334. Morphological similarities with the Saint Gaudens specimen, together with the large body mass estimate, suggest a tentative attribution of IPS4334 to cf. D. fontani, which is the largest hominoid taxon so far recorded from the Vallès-Penedès Basin. The larger size and higher robusticity of IPS4334 as compared to the Saint Gaudens specimen might be explained by the juvenile status of the latter and/or sexual dimorphism. When both specimens are considered together with a partial femur from Abocador de Can Mata, D. fontani emerges as a less suspensory ape than the late Miocene Hispanopithecus, the locomotor repertoire of the former emphasizing climbing, but still displaying a significant quadrupedal component.     

<Emphasis Type="Italic">Alansmia</Emphasis>, a new genus of grammitid ferns (Polypodiaceae) segregated from <Emphasis Type="Italic">Terpsichore</Emphasis>

Alansmia, a new genus of grammitid ferns is described and combinations are made for the 26 species known to belong to it. Alansmia is supported by five morphological synapomorphies: setae present on the rhizomes, cells of the rhizome scales turgid, both surfaces of the rhizome scales ciliate, laminae membranaceous, and sporangial capsules setose. Other diagnostic characters include pendent fronds with indeterminate growth, concolorous, orange to castaneous rhizome scales with ciliate or sometimes glandular margins, hydathodes often cretaceous, and setae simple, paired or stellate. The group also exhibits the uncommon characteristic of producing both trilete and apparently monolete spores, sometimes on the same plant. New combinations are made for Alansmia alfaroi, A. bradeana, A. canescens, A. concinna, A. contacta, A. cultrata, A. dependens, A. diaphana, A. elastica, A. glandulifera, A. heteromorpha, A. immixta, A. kirkii, A. lanigera, A. laxa, A. longa, A. monosora, A. reclinata, A. semilunaris, A. senilis, A. smithii, A. spathulata, A. stella var. stella, A. stella var. flava, A. turrialbae, A. variabilis, A. xanthotrichia. Lectotypifications are made for Alansmia concina, A. variabilis, Polypodium ciliare, P. flexile, and P. ovalescens. The genus is named in honor of pteridologist Alan R. Smith.     

Spatial and temporal patterns of floral scent emission in Dianthus inoxianus and electroantennographic responses of its hawkmoth pollinator

Scent emission is important in nocturnal pollination systems, and plant species pollinated by nocturnal insects often present characteristic odor compositions and temporal patterns of emission. We investigated the temporal (day/night; flower lifetime) and spatial (different flower parts, nectar) pattern of flower scent emission in nocturnally pollinated Dianthusinoxianus, and determined which compounds elicit physiological responses on the antennae of the sphingid pollinator Hyles livornica.The scent of D.inoxianus comprises 68 volatile compounds, but is dominated by aliphatic 2-ketones and sesquiterpenoids, which altogether make up 82% of collected volatiles. Several major and minor compounds elicit electrophysiological responses in the antennae of H. livornica. Total odor emission does not vary along day and night hours, and neither does along the life of the flower. However, the proportion of compounds eliciting physiological responses varies between day and night. All flower parts as well as nectar release volatiles. The scent of isolated flower parts is dominated by fatty acid derivatives, whereas nectar is dominated by benzenoids. Dissection (= damage) of flowers induced a ca. 20-fold increase in the rate of emission of EAD-active volatiles, especially aliphatic 2-ketones.We suggest that aliphatic 2-ketones might contribute to pollinator attraction in D. inoxianus, even though they have been attributed an insect repellent function in other plant species. We also hypothesize that the benzenoids in nectar may act as an honest signal (‘nectar guide’) for pollinators.     

Substitutions of amino acids in the pore domain of homomeric α7 nicotinic receptors for analogous residues present in heteromeric receptors modify gating, rectification and binding properties

We have studied the role of different amino acids in the M2 transmembrane domain of the α7 neuronal nicotinic receptor by mutating residues that differ from the ones located at the same positions in other α (α2-α10) or β (β2-β4) subunits. Our aim was to investigate the contribution of these amino acids to the peculiar kinetic and inward rectification properties that differentiate the homomeric α7 receptor from other nicotinic receptors. Mutations of several residues strongly modified receptor function. We found that Thr245 had the most profound effect when mutated to serine, an amino acid present in all heteromeric receptors composed of α and β subunits, by dramatically increasing the maximal current, decreasing the decaying rate of the currents and decreasing receptor rectification. Some mutants also showed altered agonist-binding properties as revealed by shifts in the dose-response curves for acetylcholine. We conclude that residues in the M2 segment and flanking regions contribute to the unusual properties of the α7 receptor, especially to its characteristic fast kinetic behavior and strong inward rectification and furthermore to the potency of agonists.