Horizontal, but not vertical, biotic interactions affect fine-scale plant distribution patterns in a low-energy system

Studies of species range determinants have traditionally focused on abiotic variables (typically climatic conditions), and therefore the recent explicit consideration of biotic interactions represents an important advance in the field. While these studies clearly support the role of biotic interactions in shaping species distributions, most examine only the influence of a single species and/or a single interaction, failing to account for species being subject to multiple concurrent interactions. By fitting species distribution models (SDMs), we examine the influence of multiple vertical (i.e., grazing, trampling, and manuring by mammalian herbivores) and horizontal (i.e., competition and facilitation; estimated from the cover of dominant plant species) interspecific interactions on the occurrence and cover of 41 alpine tundra plant species. Adding plant-plant interactions to baseline SDMs (using five field-quantified abiotic variables) significantly improved models' predictive power for independent data, while herbivore-related variables had only a weak influence. Overall, abiotic variables had the strongest individual contributions to the distribution of alpine tundra plants, with the importance of horizontal interaction variables exceeding that of vertical interaction variables. These results were consistent across three modeling techniques, for both species occurrence and cover, demonstrating the pattern to be robust. Thus, the explicit consideration of multiple biotic interactions reveals that plant-plant interactions exert control over the fine-scale distribution of vascular species that is comparable to abiotic drivers and considerably stronger than herbivores in this low-energy system.

Species distributions and interactions in a changing world : from understanding to forecasting

Les écosystèmes fournissent de nombreuses ressources et services écologiques qui sont utiles à la population humaine. La biodiversité est une composante essentielle des écosystèmes et maintient de nombreux services. Afin d'assurer la permanence des services écosystémiques, des mesures doivent être prises pour conserver la biodiversité. Dans ce but, l'acquisition d'informations détaillées sur la distribution de la biodiversité dans l'espace est essentielle. Les modèles de distribution d'espèces (SDMs) sont des modèles empiriques qui mettent en lien des observations de terrain (présences ou absences d'une espèce) avec des descripteurs de l'environnement, selon des courbes de réponses statistiques qui décrive la niche réalisée des espèces. Ces modèles fournissent des projections spatiales indiquant les lieux les plus favorables pour les espèces considérées. Le principal objectif de cette thèse est de fournir des projections plus réalistes de la distribution des espèces et des communautés en montagne pour le climat présent et futur en considérant non-seulement des variables abiotiques mais aussi biotiques. Les régions de montagne et l'écosystème alpin sont très sensibles aux changements globaux et en même temps assurent de nombreux services écosystémiques. Cette thèse est séparée en trois parties : (i) fournir une meilleure compréhension du rôle des interactions biotiques dans la distribution des espèces et l'assemblage des communautés en montagne (ouest des Alpes Suisses), (ii) permettre le développement d'une nouvelle approche pour modéliser la distribution spatiale de la biodiversité, (iii) fournir des projections plus réalistes de la distribution future des espèces ainsi que de la composition des communautés. En me focalisant sur les papillons, bourdons et plantes vasculaires, j'ai détecté des interactions biotiques importantes qui lient les espèces entre elles. J'ai également identifié la signature du filtre de l'environnement sur les communautés en haute altitude confirmant l'utilité des SDMs pour reproduire ce type de processus. A partir de ces études, j'ai contribué à l'amélioration méthodologique des SDMs dans le but de prédire les communautés en incluant les interactions biotiques et également les processus non-déterministes par une approche probabiliste. Cette approche permet de prédire non-seulement la distribution d'espèces individuelles, mais également celle de communautés dans leur entier en empilant les projections (S-SDMs). Finalement, j'ai utilisé cet outil pour prédire la distribution d'espèces et de communautés dans le passé et le futur. En particulier, j'ai modélisé la migration post-glaciaire de Trollius europaeus qui est à l'origine de la structure génétique intra-spécifique chez cette espèce et évalué les risques de perte face au changement climatique. Finalement, j'ai simulé la distribution des communautés de bourdons pour le 21e siècle afin d'évaluer les changements probables dans ce groupe important de pollinisateurs. La diversité fonctionnelle des bourdons va être altérée par la perte d'espèces spécialistes de haute altitude et ceci va influencer la pollinisation des plantes en haute altitude. - Ecosystems provide a multitude of resources and ecological services, which are useful to human. Biodiversity is an essential component of those ecosystems and guarantee many services. To assure the permanence of ecosystem services for future generation, measure should be applied to conserve biodiversity. For this purpose, the acquisition of detailed information on how biodiversity implicated in ecosystem function is distributed in space is essential. Species distribution models (SDMs) are empirical models relating field observations to environmental predictors based on statistically-derived response surfaces that fit the realized niche. These models result in spatial predictions indicating locations of the most suitable environment for the species and may potentially be applied to predict composition of communities and their functional properties. The main objective of this thesis was to provide more accurate projections of species and communities distribution under current and future climate in mountains by considering not solely abiotic but also biotic drivers of species distribution. Mountain areas and alpine ecosystems are considered as particularly sensitive to global changes and are also sources of essential ecosystem services. This thesis had three main goals: (i) a better ecological understanding of biotic interactions and how they shape the distribution of species and communities, (ii) the development of a novel approach to the spatial modeling of biodiversity, that can account for biotic interactions, and (iii) ecologically more realistic projections of future species distributions, of future composition and structure of communities. Focusing on butterfly and bumblebees in interaction with the vegetation, I detected important biotic interactions for species distribution and community composition of both plant and insects along environmental gradients. I identified the signature of environmental filtering processes at high elevation confirming the suitability of SDMs for reproducing patterns of filtering. Using those case-studies, I improved SDMs by incorporating biotic interaction and accounting for non-deterministic processes and uncertainty using a probabilistic based approach. I used improved modeling to forecast the distribution of species through the past and future climate changes. SDMs hindcasting allowed a better understanding of the spatial range dynamic of Trollius europaeus in Europe at the origin of the species intra-specific genetic diversity and identified the risk of loss of this genetic diversity caused by climate change. By simulating the future distribution of all bumblebee species in the western Swiss Alps under nine climate change scenarios for the 21st century, I found that the functional diversity of this pollinator guild will be largely affected by climate change through the loss of high elevation specialists. In turn, this will have important consequences on alpine plant pollination.

Poliamines en estrès abiòtic i mecanismes moleculars

Les poliamines (PAs) putrescina (Put), espermidina (Spd) i espermina (Spm) són mol•lècules policatiòniques de baix pes molecular, presents en els microorganismes, animals i plantes. Les PAs han estat implicades en diversos processos cel•lulars importants, incloent la resposta de les plantes a l'estrès. No obstant això, el seu mode d'acció està es desconeix. En les plantes, es van acumulant evidències de que les PAs interactuen amb macromolècules i estructures cel•lulars, com ara proteïnes de membrana, i la seva possible participació en transducció de senyals s'ha convertit en una creixent i interessant àrea d'estudi. En aquesta tesi, la possible interacció entre les poliamines i les vies de senyalització de fosfolípids és investigada. Resultats previs, han posat de manifest que alteracions en els nivells endògens de poliamines (PAs), per sobreexpressió gènica o pèrdua de funció de gens de biosíntesi, redueixen o milloren, respectivament, la capacitat de les plantes d'Arabidopsis per tolerar agressions per estrès abiòtic, produint en alguns casos notables alteracions en el desenvolupament. En aquestes plantes amb nivells alterats de PAs s'han detectat canvis importants en l'expressió gènica i s'ha trobat una connexió entre el contingut de PAs ii la biosíntesi / senyalització d'àcid abscísic (ABA). La hipòtesi actual de treball és que aquestes alteracions en l'expressió gènica poden estar mediades, si més no en part, pel catabolisme de PAs, i l’acció directa o indirecta de les espècies reactives d'oxigen (ROS) que se’n deriven.

Pathways for the synthesis of polyesters in plants; cutin, suberin, and polyhydroxyalkanoates

Plants naturally produce the lipid-derived polyester cutin, which is found in the plant cuticle that is deposited at the outermost extracellular matrix of the epidermis covering nearly all aboveground tissues. Being at the interface between the cell and the external environment, cutin and the cuticle play important roles in the protection of plants from several stresses. A number of enzymes involved in the synthesis of cutin monomers have recently been identified, including several P450s and one acyl-CoA synthetase, thus representing the first steps toward the understanding of polyester formation and, potentially, polyester engineering to improve the tolerance of plants to stresses, such as drought, and for industrial applications. However, numerous processes underlying cutin synthesis, such as a controlled polymerization, still remain elusive. Suberin is a second polyester found in the extracellular matrix, most often synthesized in root tissues and during secondary growth. Similar to cutin, the function of suberin is to seal off the respective tissue to inhibit water loss and contribute to resistance to pathogen attack. Being the main constituent of cork, suberin is a plant polyester that has already been industrially exploited. Genetic engineering may be worth exploring in order to change the polyester properties for either different applications or to increase cork production in other species. Polyhydroxyalkanoates (PHAs) are attractive polyesters of 3-hydroxyacids because of their properties as bioplastics and elastomers. Although PHAs are naturally found in a wide variety of bacteria, biotechnology has aimed at producing these polymers in plants as a source of cheap and renewable biodegradable plastics. Synthesis of PHA containing various monomers has been demonstrated in the cytosol, plastids, and peroxisomes of plants. Several biochemical pathways have been modified in order to achieve this, including the isoprenoid pathway, the fatty acid biosynthetic pathway, and the fatty acid β-oxidation pathway. PHA synthesis has been demonstrated in a number of plants, including monocots and dicots, and up to 40% PHA per gram dry weight has been demonstrated in Arabidopsis thaliana. Despite some successes, production of PHA in crop plants remains a challenging project. PHA synthesis at high level in vegetative tissues, such as leaves, is associated with chlorosis and reduced growth. The challenge for the future is to succeed in synthesis of PHA copolymers with a narrow range of monomer compositions, at levels that do not compromise plant productivity. This goal will undoubtedly require a deeper understanding of plant biochemical pathways and how carbon fluxes through these pathways can be manipulated, areas where plant "omics" can bring very valuable contributions.

Development of a retrospective job exposure matrix for PCB-exposed workers in capacitor manufacturing

Objectives: Polychlorinated biphenyls (PCBs) are considered probable human carcinogens by the International Agency for Research on Cancer and one congener, PCB126, has been rated as a known human carcinogen. A period-specific job exposure matrix (JEM) was developed for former PCB-exposed capacitor manufacturing workers (n=12,605) (1938-1977). Methods: A detailed exposure assessment for this plant was based on a number of exposure determinants (proximity, degree of contact with PCBs, temperature, ventilation, process control, job mobility). The intensity and frequency of PCB exposures by job for both inhalation and dermal exposures, and additional chemical exposures were reviewed. The JEM was developed in nine steps: (1) all unique jobs (n=1,684) were assessed using (2) defined PCB exposure determinants; (3) the exposure determinants were used to develop exposure profiles; (4) similar exposure profiles were combined into categories having similar PCB exposures; (5) qualitative intensity (high-medium-low-baseline) and frequency (continuous-intermittent) ratings were developed, and (6) used to qualitatively rate inhalation and dermal exposure separately for each category; (7) quantitative intensity ratings based on available air concentrations were developed for inhalation and dermal exposures based on equal importance of both routes of exposure; (8) adjustments were made for overall exposure, and (9) for each category the product of intensity and frequency was calculated, and exposure in the earlier era was weighted. Results: A period-specific JEM modified for two eras of stable PCB exposure conditions. Conclusions: These exposure estimates, derived from a systematic and rigorous use of the exposure determinant data, lead to cumulative PCB exposure-response relationships in the epidemiological cancer mortality and incidence studies of this cohort. [Authors]

Differential control of Notch1 gene transcription by Klf4 and Sp3 transcription factors in normal versus cancer-derived keratinocytes.

In specific cell types like keratinocytes, Notch signaling plays an important pro-differentiation and tumor suppressing function, with down-modulation of the Notch1 gene being associated with cancer development. Besides being controlled by p53, little else is known on regulation of Notch1 gene expression in this context. We report here that transcription of this gene is driven by a TATA-less "sharp peak" promoter and that the minimal functional region of this promoter, which extends from the -342 bp position to the initiation codon, is differentially active in normal versus cancer cells. This GC rich region lacks p53 binding sites, but binds Klf4 and Sp3. This finding is likely to be of biological significance, as Klf4 and, to a lesser extent, Sp3 are up-regulated in a number of cancer cells where Notch1 expression is down-modulated, and Klf4 over-expression in normal cells is sufficient to down-modulate Notch1 gene transcription. The combined knock-down of Klf4 and Sp3 was necessary for the reverse effect of increasing Notch1 transcription, consistent with the two factors exerting an overlapping repressor function through their binding to the Notch1 promoter.

Light-regulated plant growth and development.

Plants are sessile and photo-autotrophic; their entire life cycle is thus strongly influenced by the ever-changing light environment. In order to sense and respond to those fluctuating conditions higher plants possess several families of photoreceptors that can monitor light from UV-B to the near infrared (far-red). The molecular nature of UV-B sensors remains unknown, red (R) and far-red (FR) light is sensed by the phytochromes (phyA-phyE in Arabidopsis) while three classes of UV-A/blue photoreceptors have been identified: cryptochromes, phototropins, and members of the Zeitlupe family (cry1, cry2, phot1, phot2, ZTL, FKF1, and LKP2 in Arabidopsis). Functional specialization within photoreceptor families gave rise to members optimized for a wide range of light intensities. Genetic and photobiological studies performed in Arabidopsis have shown that these light sensors mediate numerous adaptive responses (e.g., phototropism and shade avoidance) and developmental transitions (e.g., germination and flowering). Some physiological responses are specifically triggered by a single photoreceptor but in many cases multiple light sensors ensure a coordinated response. Recent studies also provide examples of crosstalk between the responses of Arabidopsis to different external factors, in particular among light, temperature, and pathogens. Although the different photoreceptors are unrelated in structure, in many cases they trigger similar signaling mechanisms including light-regulated protein-protein interactions or light-regulated stability of several transcription factors. The breath and complexity of this topic forced us to concentrate on specific aspects of photomorphogenesis and we point the readers to recent reviews for some aspects of light-mediated signaling (e.g., transition to flowering).

Radial transport of nutrients: the plant root as a polarized epithelium.

In higher plants, roots acquire water and soil nutrients and transport them upward to their aerial parts. These functions are closely related to their anatomical structure; water and nutrients entering the root first move radially through several concentric layers of the epidermis, cortex, and endodermis before entering the central cylinder. The endodermis is the innermost cortical cell layer that features rings of hydrophobic cell wall material called the Casparian strips, which functionally resemble tight junctions in animal epithelia. Nutrient uptake from the soil can occur through three different routes that can be interconnected in various ways: the apoplastic route (through the cell wall), the symplastic route (through cellular connections), and a coupled trans-cellular route (involving polarized influx and efflux carriers). This Update presents recent advances in the radial transport of nutrients highlighting the coupled trans-cellular pathway and the roles played by the endodermis as a barrier.

The cuticle: Not only a barrier for plant defence: A novel defence syndrome in plants with cuticular defects.

The cuticle is a physical barrier that prevents water loss and protects against irradiation, xenobiotics and pathogens. This classic textbook statement has recently been revisited and several observations were made showing that this dogma falls short of being universally true. Both transgenic Arabidopsis thaliana lines expressing cell wall-targeted fungal cutinase (so-called CUTE plants) or lipase as well as several A. thaliana mutants with altered cuticular structure remained free of symptoms after an inoculation with Botrytis cinerea. The alterations in cuticular structure lead to the release of fungitoxic substances and changes in gene expression that form a multifactorial defence response. Several models to explain this syndrome are discussed.

Relatedness among arbuscular mycorrhizal fungi drives plant growth and intraspecific fungal coexistence.

Arbuscular mycorrhizal fungi (AMF) form symbioses with most plant species. They are ecologically important determinants of plant growth and diversity. Considerable genetic variation occurs in AMF populations. Thus, plants are exposed to AMF of varying relatedness to each other. Very little is known about either the effects of coexisting AMF on plant growth or which factors influence intraspecific AMF coexistence within roots. No studies have addressed whether the genetics of coexisting AMF, and more specifically their relatedness, influences plant growth and AMF coexistence. Relatedness is expected to influence coexistence between individuals, and it has been suggested that decreasing ability of symbionts to coexist can have negative effects on the growth of the host. We tested the effect of a gradient of AMF genetic relatedness on the growth of two plant species. Increasing relatedness between AMFs lead to markedly greater plant growth (27% biomass increase with closely related compared to distantly related AMF). In one plant species, closely related AMF coexisted in fairly equal proportions but decreasing relatedness lead to a very strong disequilibrium between AMF in roots, indicating much stronger competition. Given the strength of the effects with such a shallow relatedness gradient and the fact that in the field plants are exposed to a steeper gradient, we consider that AMF relatedness can have a strong role in plant growth and the ability of AMF to coexist. We conclude that AMF relatedness is a driver of plant growth and that relatedness is also a strong driver of intraspecific coexistence of these ecologically important symbionts.

Coupled reproductive ecologies in a plant-pollinator-seed predator system

Résumé de la thèseBien que le mutualisme puisse être considéré comme une relation harmonieuse entre différentes espèces, son étude révèle plutôt une exploitation réciproque où chaque partenaire tente de maximiser ses bénéfices tout en réduisant ses coûts. Dans ce contexte, l'identification des facteurs qui favorisent ou contrarient, au cours de l'évolution, une issue mutualiste est une étape majeure pour pouvoir reconstruire les étapes clés menant à l'apparition et au maintien des interactions mutualistes. Le but de ce doctorat était l'identification des traits phénotypiques qui permettent à la plante Silene latofolia (Caryophyllacée)et à son pollinisateur - prédateur de graines, la phalène Hadena bicruris (Noctuidé), d'augmenter les bénéfices nets que chacun retire de l'interaction. Ce système d'étude est particulièrement bien approprié à l'étude de ces traits, car on peut assez facilement estimer la qualité et la quantité des descendants (fitness) des deux partenaires. En effet, la femelle papillon pond un oeuf dans la fleur qu'elle pollinise et sa larve se développe dans le fruit, consommant les graines de la plante. Ainsi, sur une même plante, il est possible d'estimer les succès respectifs de la plante et du papillon à obtenir une descendance. De plus, le conflit d'intérêt autour des graines qui sont indispensables, à la fois à la plante et au papillon, peut stimuler l'évolution de traits qui limitent la surexploitation réciproque des partenaires. Dans une première étude, j'ai montré que le papillon mâle était un pollinisateur efficace de S. latifolia et qu'ainsi, il permettait à la plante d'augmenter le nombre de graines produites (i.e.bénéfice) sans pour autant augmenter la quantité de larves sur la plante. Dans ce système, les papillons pondent un seul oeuf par fleur, déposé soit à l'intérieur de la fleur, dans le tube de corolle, soit sur le pétale. Ma seconde étude montre que les plantes répondent différemment à la présence des oeufs suivant leur position. Aussi, quand l'oeuf est placé dans la fleur, la plante a davantage tendance à ne pas développer le fruit de la fleur infesté ou bien à produire des fruits plus petits que lorsque l'oeuf est placé sur le pétale. Enfin, j'ai montré que la femelle du papillon pond plus souvent sur le pétale lorsque elle visite des fleurs dotées d'un long tube de corolle, et que les larves issues de ces oeufs ont moins de chances de réussir à pénétrer dans le fruit que les larves issues des oeufs placés à l'intérieur de la fleur. Aussi, la variation observée du site de ponte pourrait être causé par la morphologie de la fleur qui contraint le papillon à pondre sur le pétale. Vu dans leur ensemble, les résultats obtenus pendant ce doctorat suggèrent que la participation des mâles à la pollination, l'absence de développement des fruits et la profondeur du tube de corolle pourraient réduire les coûts que S. latifolia subit dans son interaction avec H. bicruris. Par ailleurs, je n'ai pas détecté de mécanismes qui permettraient au papillon de réduire les coûts que la plante pourrait lui imposer. La prochaine étape serait de déterminer l'effet des traits identifiés dans ce doctorat sur la fitness globale de la plante et du papillon pour estimer pleinement leur efficacité à réduire les coûts et à favoriser une issue mutualiste. De même, il faudrait évaluer l'effet de ces traits en populations naturelles pour identifier le rôle des facteurs environnementaux sur leur efficacité.AbstractAlthough mutualisms can be regarded as harmonious relationships between the interacting partners, they are best conceptualized as reciprocal exploitations in which each partner attempts to increase its own benefits and decrease its costs. To date, identifying the factors which promote or discourage mutualistic outcomes remains a major goal to reconstruct the ecological conditions leading to mutualisms. The aim of this PhD thesis was to identify phenotypic traits that may increase the net benefits of each partner in the interaction between the plant Silene latifolia (Caryophyllaceae) and its pollinator / seed predator, the moth Hadena bicruris (Noctuidae). This study system is particularly well suited because the fitness of both interacting species can be assessed. The female moth lays its egg in the flower it pollinated, and its offspring grows in the fruit, feeding on the seeds of the plant, which allows for the follow-up of both larva and fruit fates. Furthermore, the inherent conflict of interest over the seeds as plant progeny vs. larval resource may stimulate the evolution of traits that reduce overexploitation in both the moth and plant. In a first study, I show that male moths are efficient pollinators, hence increasing seed production without increasing oviposition. The contribution of male moths to pollination might thus improve the net benefits of the interaction for the host plant. Females of the H. bicruris moth lay a single egg per flower, and place it either inside the corolla tube or on the petal. My second study shows that plants are more likely to abort the infested flower or to produce a smaller fruit when the egg was experimentally placed inside the flower compared to plants that received an egg on the petal. Finally, female moths were found to lay their eggs more frequently on the petal when visiting a flower with a deep corolla tube, and larvae hatching from these eggs less likely to successfully attack the fruit. Variation in egg position on the flower may thus be the result of a constraint imposed by floral morphology. Overall, this PhD work suggests that the pollination by male moths, flower abortion, and deep corolla tube may efficiently reduce the costs experienced by S. latifolia in its interaction with H. bicruris. Interestingly, no apparent mechanism of costs reduction was detected for the moth. Further studies should focus on the effects of these traits (i) in the long term fitness of both the plant and the insect and (ii) their interactions with environmental factors (biotic and abiotic) that may affect their efficiency in natural populations.

HA-1 and the SMCY-derived peptide FIDSYICQV (H-Y) are immunodominant minor histocompatibility antigens after bone marrow transplantation.

BACKGROUND: Allogeneic bone marrow donors can be incompatible at different levels. Even HLA-identical pairs will be still incompatible for numerous minor histocompatibility antigens (mHag). Nevertheless, some incompatibilities are found to be associated with an increased risk of graft-versus-host disease (GVHD), which could be related to the way the immune system recognizes these antigens. METHODS: We determined the specificity of cytotoxic T-cell clones isolated during acute GVHD or during bone marrow graft rejection in patients (n=14) transplanted with marrow from donors who were histoincompatible for different minor and/or major histocompatibility antigens. RESULTS: We found a clear hierarchy among the different types of histoincompatibilities. In three combinations mismatched for a class I allele, all 27 clones isolated during GVHD were specific for the incompatible HLA molecule. In the 11 class I-identical combinations, 14 different mHags were recognized. The mHag HA-1, known to have a significant impact on the development of GVHD, was recognized in the two HA-1-incompatible combinations. In one of these combinations, which was sex mismatched, all 56 clones analyzed were directed against HA-1, demonstrating the dominance of this mHag. In the four HA-1-compatible, sex-mismatched combinations, the anti-H-Y response was directed against one immunodominant epitope rather than against multiple Y-chromosome-encoded epitopes. All male specific cytotoxic T lymphocytes (n=15) recognized the same high-performance liquid chromatography-purified peptide fraction presented by T2 cells. Moreover, all cytotoxic T lymphocytes tested (n=6) were specific for the SMCY-derived peptide FIDSYICQV, originally described as being the H-Y epitope recognized in the context of HLA-A*0201. CONCLUSIONS: Some histocompatibility antigens are recognized in an immunodominant fashion and will therefore be recognized in the majority of mismatched combinations. Only for such antigens, correlations between mismatches and the occurrence of GVHD or graft rejections will be found.

Heterogeneity in endothelium-derived nitric oxide-mediated relaxation of different sized pulmonary arteries of newborn lambs.

Endothelium-derived nitric oxide (EDNO) plays a pivotal role in regulating pulmonary circulation. To determine whether there is a heterogeneity in EDNO-mediated responses of different sized pulmonary vessels, we studied small and large isolated pulmonary arteries of newborn lambs (diameter, 0.4-0.7 and 1.5-2.5 mm, respectively). The isometric tension of vessel rings were recorded while suspended in organ chambers filled with modified Krebs-Ringer bicarbonate solution (95% O2-5% CO2, 37 degrees C). In vessels preconstricted with norepinephrine, acetylcholine and bradykinin induced a greater relaxation of small pulmonary arteries than of large pulmonary arteries. Acetylcholine, bradykinin, and nitric oxide also induced a greater increase in cGMP content in small arteries than in large ones. The responses to acetylcholine and bradykinin were endothelium-dependent and inhibited by nitro-L-arginine, an inhibitor of nitric oxide synthase. In vessels without endothelium, the response to nitric oxide was inhibited by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, an inhibitor of soluble guanylate cyclase. The activity of soluble guanylyl cyclase of small arteries was greater than that of large arteries under basal conditions and after stimulation with S-nitroso-N-acetylpenicillamine, a nitric oxide donor. These results demonstrate that heterogeneity exists in EDNO-mediated relaxation of small and large pulmonary arteries in newborn lambs. A difference in the soluble guanylate cyclase activity of vascular smooth muscle may have contributed to this phenomenon.

Antimicrobial peptide genes in Bacillus strains from plant environments

The presence of the antimicrobial peptide (AMP) biosynthetic genes srfAA (surfactin), bacA (bacylisin), fenD (fengycin), bmyB (bacyllomicin), spaS (subtilin), and ituC (iturin) was examined in 184 isolates of Bacillus spp. obtained from plant environments (aerial, rhizosphere, soil) in the Mediterranean land area of Spain. Most strains had between two and four AMP genes whereas strains with five genes were seldom detected and none of the strains had six genes. The most frequent AMP gene markers were srfAA, bacA, bmyB, and fenD, and the most frequent genotypes srfAA-bacA-bmyB and srfAAbacA-bmyB-fenD. The dominance of these particular genes in Bacillus strains associated with plants reinforces the competitive role of surfactin, bacyllomicin, fengycin, and bacilysin in the fitness of strains in natural environments. The use of these AMP gene markers may assist in the selection of putative biological control agents of plant pathogens