Mobile gibberellin directly stimulates Arabidopsis hypocotyl xylem expansion.

Secondary growth of the vasculature results in the thickening of plant structures and continuously produces xylem tissue, the major biological carbon sink. Little is known about the developmental control of this quantitative trait, which displays two distinct phases in Arabidopsis thaliana hypocotyls. The later phase of accelerated xylem expansion resembles the secondary growth of trees and is triggered upon flowering by an unknown, shoot-derived signal. We found that flowering-dependent hypocotyl xylem expansion is a general feature of herbaceous plants with a rosette growth habit. Flowering induction is sufficient to trigger xylem expansion in Arabidopsis. By contrast, neither flower formation nor elongation of the main inflorescence is required. Xylem expansion also does not depend on any particular flowering time pathway or absolute age. Through analyses of natural genetic variation, we found that ERECTA acts locally to restrict xylem expansion downstream of the gibberellin (GA) pathway. Investigations of mutant and transgenic plants indicate that GA and its signaling pathway are both necessary and sufficient to directly trigger enhanced xylogenesis. Impaired GA signaling did not affect xylem expansion systemically, suggesting that it acts downstream of the mobile cue. By contrast, the GA effect was graft transmissible, suggesting that GA itself is the mobile shoot-derived signal.

Fat oxidation kinetics during exercise in obese individuals

Introduction An impaired ability to oxidize fat may be a factor in the obesity's aetiology (3). Moreover, the exercise intensity (Fatmax) eliciting the maximal fat oxidation rate (MFO) was lower in obese (O) compared with lean (L) individuals (4). However, difference in fat oxidation rate (FOR) during exercise between O and L remains equivocal and little is known about FORs during high intensities (>60% ) in O compared with L. This study aimed to characterize fat oxidation kinetics over a large range of intensities in L and O. Methods 12 healthy L [body mass index (BMI): 22.8±0.4] and 16 healthy O men (BMI: 38.9±1.4) performed submaximal incremental test (Incr) to determine whole-body fat oxidation kinetics using indirect calorimetry. After a 15-min resting period (Rest) and 10-min warm-up at 20% of maximal power output (MPO, determined by a maximal incremental test), the power output was increased by 7.5% MPO every 6-min until respiratory exchange ratio reached 1.0. Venous lactate and glucose and plasma concentration of epinephrine (E), norepinephrine (NE), insulin and non-esterified fatty acid (NEFA) were assessed at each step. A mathematical model (SIN) (1), including three variables (dilatation, symmetry, translation), was used to characterize fat oxidation (normalized by fat-free mass) kinetics and to determine Fatmax and MFO. Results FOR at Rest and MFO were not significantly different between groups (p≥0.1). FORs were similar from 20-60% (p≥0.1) and significantly lower from 65-85% in O than in L (p≤0.04). Fatmax was significantly lower in O than in L (46.5±2.5 vs 56.7±1.9 % respectively; p=0.005). Fat oxidation kinetics was characterized by similar translation (p=0.2), significantly lower dilatation (p=0.001) and tended to a left-shift symmetry in O compared with L (p=0.09). Plasma E, insulin and NEFA were significantly higher in L compared to O (p≤0.04). There were no significant differences in glucose, lactate and plasma NE between groups (p≥0.2). Conclusion The study showed that O presented a lower Fatmax and a lower reliance on fat oxidation at high, but not at moderate, intensities. This may be linked to a: i) higher levels of insulin and lower E concentrations in O, which may induce blunted lipolysis; ii) higher percentage of type II and a lower percentage of type I fibres (5), and iii) decreased mitochondrial content (2), which may reduce FORs at high intensities and Fatmax. These findings may have implications for an appropriate exercise intensity prescription for optimize fat oxidation in O. References 1. Cheneviere et al. Med Sci Sports Exerc. 2009 2. Holloway et al. Am J Clin Nutr. 2009 3. Kelley et al. Am J Physiol. 1999 4. Perez-Martin et al. Diabetes Metab. 2001 5. Tanner et al. Am J Physiol Endocrinol Metab. 2002

Arabidopsis lox3 lox4 double mutants are male sterile and defective in global proliferative arrest.

Fertility and flower development are both controlled in part by jasmonates, fatty acid-derived mediators produced via the activity of 13-lipoxygenases (13-LOXs). The Arabidopsis thaliana Columbia-0 reference genome is predicted to encode four of these enzymes and it is already known that one of these, LOX2, is dispensable for fertility. In this study, the roles of the other three 13-LOXs (LOX3, LOX4 and LOX6) were investigated in single and double mutants. Four independent lox3 lox4 double mutants assembled with different mutated lox3 and lox4 alleles had fully penetrant floral phenotypes, displaying abnormal anther maturation and defective dehiscence. The plants were no longer self-fertile and pollen was not viable. Fertility in the double mutant was restored genetically by complementation with either the LOX3 or the LOX4 cDNAs and biochemically with exogenous jasmonic acid. Furthermore, deficiency in LOX3 and LOX4 causes developmental dysfunctions, compared to wild type; lox3 lox4 double mutants are taller and develop more inflorescence shoots and flowers. Further analysis revealed that developmental arrest in the lox3 lox4 inflorescence occurs with the production of an abnormal carpelloid flower. This distinguishes lox3 lox4 mutants from the wild type where developmentally typical flower buds are the terminal inflorescence structures observed in both the laboratory and in nature. Our studies of lox3 lox4 as well as other jasmonic acid biosynthesis and perception mutants show that this plant hormone is not only required for male fertility but also involved in global proliferative arrest.

Meadow Saffron Used as a Spice

Introduction: Intoxications with colchicine usually occur by ingestion of meadow saffron leaves (Colchicum autumnale) which are mistakenly collected for alimentary purposes instead of the leaves of crow garlic (Allium ursinum). Colchicine, the main alkaloid of Colchicum autumnale, is present in all parts of the plant. We report a rarer source of mistake, i.e. between the flowers of Colchicum autumnale and Crocus sativus. The similarity in this case is limited to the appearance of the flowers, but Colchicum autumnale, which is also flowering in autumn, lacks the crimson stigma from which the saffron spice is derived from Crocus sativus. Case report: A 47-year-old woman collected the stamens of a flower resembling Crocus sativus for use as saffron. Her knowledge about Crocus sativus was limited to having seen this plant previously at a museum of saffron (Mund, Switzerland). She prepared a meal with rice using three pinches of ''saffron'' for ten tablespoons of rice. She and her 8-year-old child, both ate the usual amount of rice (6 and 2 tablespoons, respectively). The 2 brothers (4- and 9-years-old) only ate 3 teaspoons of rice each. A slightly bitter taste and the absence of a yellow colouration were peculiar. Three to four hours after the meal, the mother developed nausea and contacted the Swiss Toxicological Information Centre, suspecting a plant misidentification. All family members were referred to the regional university hospital for administration of oral activated charcoal. No other symptoms were reported, notably no symptoms in the 8-year-old boy and his brothers. Colchicine serum concentration (blood sample obtained 15 hours after ingestion) measured by HPLC-mass spectrometry was 0.36 mg/L for the mother, and 0.13 mg/L for the 8-year-old child, respectively (therapeutic levels: 0.30-2.5 mg/L). Conclusion: This report demonstrates that a significant amount of colchicine may be absorbed even after ingestion of very small quantities of Colchicum autumnale, which in this case was confused with Crocus sativus. Serum colchicine concentrations in the sub-/therapeutic range can be quantified by HPLC-mass spectrometry, which allows a very sensitive and specific detection of this alkaloid in blood and urine.

Fat oxidation kinetics : effect of exercise

ABSTRACT Fat oxidation kinetics: effect of exercise. During graded exercise, absolute whole body fat oxidation rates increase from low to moderate intensities, and then markedly decline at high intensities, implying an exercise intensity (Fatmax) at which the fat oxidation rate is maximal (MFO). The main aim of the present work was to examine the effect of exercise on whole body fat oxidation kinetics. For this purpose, a sinusoidal mathematical model (SIN) has been developped in the first study to provide an accurate description of the shape of fat oxidation kinetics during graded exercise, represented as a function of exercise intensity, and to determine Fatmax and MFO. The SIN model incorporates three independent variables (i.e., dilatation, symmetry, and translation) that correspond to main expected modulations of the basic fat oxidation curve because of factors such as mode of exercise or training status. The results of study 1 showed that the SIN model was a valuable tool to determine Fatmax and MFO, and to precisely characterize and quantify the different shape of fat oxidation kinetics through its three variables. The effectiveness of the SIN model to detect differences in fat oxidation kinetics induced by a specific factor was then confirmed in the second study, which quantitatively described and compared fat oxidation kinetics in two different popular modes of exercise: running and cycling. It was found that the mean fat oxidation kinetics during running was characterized by a greater dilatation and a rightward asymmetry compared with the symmetric parabolic curve in cycling. In the two subsequent studies, the effect of a prior endurance exercise of different intensities and durations on whole body fat oxidation kinetics was examined. Study 3 determined the impact of a 1-h continuous exercise bout at an exercise intensity corresponding to Fatmax on fat oxidation kinetics during a subsequent graded test, while study 4 investigated the effect of an exercise leading to a more pronounced muscle glycogen depletion. The results of these two latter studies showed that fat oxidation rates, MFO, and Fatmax were enhanced following endurance exercise, but were increased to a greater extent with a more severe mucle glycogen depletion, inducing therefore modifications in the postexercise fat oxidation kinetics (i.e., greater dilatation and rightward asymmetry). In perspective, further studies have been suggested 1) to assess physiological meaning of the three independent variables of the SIN model; and 2) to compare the effect of two different training programs on fat oxidation kinetics in obese subjects.

Are the light-harvesting I complexes from Rhodospirillum rubrum arranged around the reaction centre in a square geometry?

The basic photosynthetic unit containing the reaction centre and the light-harvesting I complex (RC-LHI) of the purple non-sulphur bacterium Rhodospirillum rubrum was purified and reconstituted into two-dimensional (2D) membrane crystals. Transmission electron microscopy using conventional techniques and cryoelectron microscopy of the purified single particles and of 2D crystals yielded a projection of the RC-LHI complex at a resolution of at least 1.6 nm. In this projection the LHI ring appears to have a square symmetry and packs in a square crystal lattice. The square geometry of the LHI ring was observed also in images of single isolated particles of the RC-LHI complex. However, although the LHI units are packed identically within the crystal lattice, a new rotational analysis developed here showed that the reaction centres take up one of four possible orientations within the ring. This fourfold disorder supports our interpretation of a square ring symmetry and suggests that a hitherto undetected component may be present within the photosynthetic unit.

Fat oxidation kinetics during exercise in obese individuals.

Introduction An impaired ability to oxidize fat may be a factor in the obesity's aetiology (3). Moreover, the exercise intensity (Fatmax) eliciting the maximal fat oxidation rate (MFO) was lower in obese (O) compared with lean (L) individuals (4). However, difference in fat oxidation rate (FOR) during exercise between O and L remains equivocal and little is known about FORs during high intensities (>60% ) in O compared with L. This study aimed to characterize fat oxidation kinetics over a large range of intensities in L and O. Methods 12 healthy L [body mass index (BMI): 22.8±0.4] and 16 healthy O men (BMI: 38.9±1.4) performed submaximal incremental test (Incr) to determine whole-body fat oxidation kinetics using indirect calorimetry. After a 15-min resting period (Rest) and 10-min warm-up at 20% of maximal power output (MPO, determined by a maximal incremental test), the power output was increased by 7.5% MPO every 6-min until respiratory exchange ratio reached 1.0. Venous lactate and glucose and plasma concentration of epinephrine (E), norepinephrine (NE), insulin and non-esterified fatty acid (NEFA) were assessed at each step. A mathematical model (SIN) (1), including three variables (dilatation, symmetry, translation), was used to characterize fat oxidation (normalized by fat-free mass) kinetics and to determine Fatmax and MFO. Results FOR at Rest and MFO were not significantly different between groups (p≥0.1). FORs were similar from 20-60% (p≥0.1) and significantly lower from 65-85% in O than in L (p≤0.04). Fatmax was significantly lower in O than in L (46.5±2.5 vs 56.7±1.9 % respectively; p=0.005). Fat oxidation kinetics was characterized by similar translation (p=0.2), significantly lower dilatation (p=0.001) and tended to a left-shift symmetry in O compared with L (p=0.09). Plasma E, insulin and NEFA were significantly higher in L compared to O (p≤0.04). There were no significant differences in glucose, lactate and plasma NE between groups (p≥0.2). Conclusion The study showed that O presented a lower Fatmax and a lower reliance on fat oxidation at high, but not at moderate, intensities. This may be linked to a: i) higher levels of insulin and lower E concentrations in O, which may induce blunted lipolysis; ii) higher percentage of type II and a lower percentage of type I fibres (5), and iii) decreased mitochondrial content (2), which may reduce FORs at high intensities and Fatmax. These findings may have implications for an appropriate exercise intensity prescription for optimize fat oxidation in O. References 1. Cheneviere et al. Med Sci Sports Exerc. 2009 2. Holloway et al. Am J Clin Nutr. 2009 3. Kelley et al. Am J Physiol. 1999 4. Perez-Martin et al. Diabetes Metab. 2001 5. Tanner et al. Am J Physiol Endocrinol Metab. 2002

Extraction and concentration of vapors from fire debris for forensic purposes: evaluation of the use of Radiello Passive Air Sampler

The Radiello Passive Air Sampler is one of the latest innovations developed for the sampling of pollutants in the air by passive headspace. It has been reported that its properties allow an enhanced sensitivity, reproducibility and adsorption capacity. It therefore appears to be of interest in the extraction of potential residues of ignitable liquids present in fire debris when arson is suspected. A theoretical approach and several laboratory tests have made it possible to precisely characterize in a forensic perspective the potential of the device in extracting and concentrating the vapors of ignitable liquids found in fire debris. Despite some advantages, the Radiello device appears to be less efficient than traditional axial symmetry samplers.

Sperm velocity in an Alpine whitefish: effects of age, size, condition, fluctuating asymmetry and gonad abnormalities

The relationship between sperm velocity and individual age, size, body condition and fluctuating asymmetry was investigated in Alpine whitefish Coregonus fatioi. The fish analysed belonged to one among several sympatric whitefish populations of Lake Thun, Switzerland, which are characterized by a high prevalence of gonad alterations. Therefore, sperm velocity data were also tested for a link between gonad deformation and sperm swimming speed. Sperm velocity was significantly lower in larger-grown individuals and in individuals of higher body condition. As expected, sperm velocity was higher in males with higher levels of fluctuating asymmetry, but it did not significantly vary with male age. Moreover, variation in sperm velocity was found to be significantly higher in individuals showing some types of gonad alterations but it did not significantly correlate with the presence of other types of alterations. (C) 2007 The Authors Journal compilation (C) 2007 The Fisheries Society of the British Isles.

Mechanisms involved in the maintenance of inbreeding depression in gynodioecious "Silene vulgaris" (Caryophyllaceae): an experimental investigation

Summary Gynodioecy, the joint occurrence of females and hermaphrodites within natural populations, is a widely studied mating system ever since Darwin (1877). It is an exceptional mating system because continuous selection is necessary to maintain it. Since females only reproduce through ovules whereas hermaphrodites transmit genes through ovules and pollen, larger female fitness, in terms of seed output, is required to allow their maintenance. Two non-exclusive mechanisms can account for the maintenance of females. First, as females do not produce pollen they can reallocate their resources towards a higher ovule production. Second, hermaphrodites can self- and cross-fertilize whereas females are obligate outcrossers. Thus hermaphrodites should partly suffer from inbreeding depression (i.e.: the fitness decline of inbred relative to outbred individuals) and thereby produce less fit progeny than females. This thesis investigated the effects of self- and cross-fertilization of heimaphrodites over two consecutive generations. Inbreeding depression increased across the successive stages of the life- cycle (i.e.: from "seed traits" to "reproductive traits") displaying large inbreeding depression estimates (up to 0.76). This investigation not only detected large inbreeding depression estimates but also detected mechanisms involved in the maintenance of inbreeding depression. For instance cryptic self-incompatibility which is here a larger in vivo pollen performance of distant pollen compared to self-pollen; the expression of inbreeding depression especially in late life-cycle stages, and the appearance of females in the progeny of selfed hermaphrodites. The female biased sex ratio in the progeny of selfed hermaphrodites was a surprising result and could either come from the sex determining mechanisms (complex nucleo-cytoplasmic interaction(s)) and/or from inbreeding depression. Indeed, we not only got females and hermaphrodites but also partial male-sterile (PMS) individuals (i.e.: individuals with differing number of viable stamens). We detected that inbred pollen bearing plants (excluding females) have less viable stamens per flower than outbred plants. A positive correlation was detected between inbreeding depression for the number of viable stamens per flower and the difference in sex ratio between inbred and outbred individuals. A positive relationship was also detected between inbreeding depression for pollen viability and inbreeding depression for number of viable stamens per flower. Each correlation can either account for pleiotropic effects (a major gene acting on the two considered traits) or linkage disequilibrium between genes controlling each of the two related traits. If we hypothesize that these correlations are due to a major gene with pleiotropic effects, the positive relationship between inbreeding depression for number of viable stamens per flower and inbreeding depression for pollen viability showed that deleterious alleles present on a major gene coding for pollen production and viability depressed male fitness within inbred plants. The positive relationship between sex ratio difference between inbred and outbred individuals and inbreeding depression for number of viable stamens per flower indicates that (1) either number of viable stamens per flower is, in addition to inbreeding, also affected by the loci coding for sex determinism or, (2) the presence of females within the progeny of selfed hermaphrodites is a consequence of large inbreeding depression inhibiting pollen production, or (3) sex is here determined by a combination of loci coding for sex expression and inbreeding depression for male reproductive traits. In conclusion, Silene vulgaris has been shown to be a good model for understanding the evolution of mating systems that promote outbreeding. Résumé La gynodïoécie est définie comme étant la présence simultanée d'hermaphrodites et de femelles au sein de populations naturelles d'une même espèce. Ce système de reproduction a toujours fasciné le monde scientifique depuis Darwin, comme en témoigne ses écrits (1876, 1877) sur les systèmes de reproduction chez les plantes. Les femelles ne transmettent leurs gènes qu'à travers leurs ovules alors que les hermaphrodites transmettent leurs gènes à la fois par la voie mâle (le pollen) et la voie femelle (les ovules). La condition pour que la gynodïoécie se maintienne nécessite donc une fitness de la fonction femelle plus élevée chez les femelles que chez les hermaphrodites. Deux mécanismes mutuellement non exclusifs peuvent expliquer le maintien des femelles au sein de ces populations gynodioïques. D'une part, les femelles peuvent réallouer les ressources non utilisées pour la production de pollen et peuvent par conséquent produire plus d'ovules. D'autre part, la reproduction des femelles ne peut se faire que par allo-fécondation alors que les hermaphrodites, peuvent se reproduire à la fois par auto- et allo-fécondation. L'autofécondation s'accompagne en général d'une diminution de fitness de la descendance relativement à la progéniture issue d'allo-fécondation ; ce phénomène est connu sous le nom de dépression de consanguinité. Cette thèse avait pour but de mettre en évidence une éventuelle dépression de consanguinité chez Silene vulgaris, une espèce gynodioïque. Des hermaphrodites, issus de trois vallées alpines, ont été auto- et allo¬fécondés sur deux générations successives. La dépression de consanguinité pouvant s'exprimer à tous les stades de vie d'un individu, plusieurs traits de fitness, allant du nombre de graines par fruit à la production de gamètes ont été mesurés sur différents stades de vie successifs. L'estimation de la dépression de consanguinité totale atteignait des valeurs allant de 0.52 à 0.76 selon la vallée considérée, ce qui indiquerait que les hermaphrodites ont tout intérêt à limiter l'autofécondation et que les femelles ne devraient pas avoir de peine à subsister dans les vallées étudiées. Par la même occasion des mécanismes diminuant la purge potentielle du fardeau génétique, et permettant ainsi le maintien du « niveau » de dépression de consanguinité et par conséquence le maintien de la gynodïoécie ont été mis en évidence. En effet, nos résultats montrent que la dépression de consanguinité s'exprimait tard dans le cycle de vie permettant ainsi à un certain nombre individus consanguins de transmettre leurs allèles délétères à la génération suivante. D'autre part, la croissance in vivo des tubes polliniques d'auto-pollen était plus lente que celle de l'allo-pollen et donc en situation de compétition directe, les ovules devraient plutôt être issus d'allo-fécondation, diminuant ainsi les chances de purges d'allèles délétères. Enfin, l'apparition de femelles dans la progéniture d'hermaphrodites autofécondés diminue aussi les chances de purge d'allèles délétères. Il nous a été impossible de déterminer si l'apparition de femelles dans la descendance d'hermaphrodites autofécondés était due au déterminisme génétique du sexe ou si la différence de sexe ratio entre la descendance auto- et allo-fécondée était due à une éventuelle dépression de consanguinité inhibant la production de pollen. Nous avons observé que S. vulgaris ne présentaient pas uniquement des hermaphrodites et des femelles mais aussi toute sorte d'individus intermédiaires avec un nombre variable d'étamines viables. Nous avons pu mettre' en évidence des corrélations positives entre (1) la différence de sexe ratio (la proportion d'individus produisant du pollen) entre individus consanguins et non consanguins et une estimation de la dépression de consanguinité pour le nombre d'étamines viables d'individus produisant du pollen, ainsi qu'entre (2) la dépression de consanguinité pour le nombre d'étamines viables et celle estimée pour la viabilité du pollen. Chaque corrélation indique soit l'effet d'un (ou plusieurs) gène(s) pléiotropique(s), soit un déséquilibre de liaison entre les gènes. En considérant que ces corrélations sont le résultat d'effet pléiotropiques, la relation entre le nombre d'étamines viables par fleur et la viabilité du pollen, indiquerait un effet négatif de la consanguinité sur la production et la viabilité du pollen due partiellement à un gène majeur. La seconde corrélation indiquerait soit que les gènes responsables de la détermination du sexe agissent aussi sur l'expression de la fonction mâle soit que l'expression du sexe est sujette à la dépression de consanguinité, ou encore un mélange des deux. Aux regards de ces résultats, Silene vulgaris s'est avéré être un bon modèle de compréhension de l'évolution des systèmes de reproduction vers la séparation des sexes.

Gender differences in whole body fat oxidation kinetics during exercise

Introduction Discrepancies appear in studies comparing fat oxidation between men and women during exercise (1). Therefore, this study aimed to quantitatively describe and compare whole body fat oxidation kinetics between genders during exercise using a sinusoidal model (SIN) (2). Methods Twelve men and 11 women matched for age, body mass index (23.4±0.6 kg.m-2 and 21.5±0.8 kg.m-2, respectively) and aerobic fitness [maximal oxygen uptake ( ) (58.5±1.6 mL.kg FFM-1.min-1 and 55.3±2.0 mL.kg FFM-1.min-1, respectively) and power output ( ) per kilogram of fat-free mass (FFM)] performed submaximal incremental tests (Incr) with 5-min stages and 7.5% increment on a cycle ergometer. Respiratory and HR values were averaged over the last 2 minutes of each stage. All female study participants were eumenorrheic, reported regular menstrual cycles (28.6 ± 0.8 days) and were not taking oral contraceptives (OC) or other forms of exogenous ovarian hormones. Women were studied in the early follicular phase (FP) of their menstrual cycle (between days 3 and 8, where day 1 is the first day of menses). Fat oxidation rates were determined using indirect calorimetry and plotted as a function of exercise intensity. The SIN model (2), which includes three independent variables (dilatation, symmetry, translation), was used to mathematically describe fat oxidation kinetics and to determine the intensity (Fatmax) eliciting the maximal fat oxidation (MFO). Results During Incr, women exhibited greater fat oxidation rates from 35 to 85% , MFO (6.6 ± 0.9 vs. 4.5 ± 0.3 mgkg FFM-1min-1) and Fatmax (58.1 ± 1.9 vs. 50.0 ± 2.7% ) (P<0.05) than men. While men and women showed similar global shapes of fat oxidation kinetics in terms of dilatation and symmetry (P>0.05), the fat oxidation curve tended to be shifted towards higher exercise intensities in women (rightward translation, P=0.08). Conclusion These results showed that women, eumenorrheic, not taking OC and tested in FP, have a greater reliance on fat oxidation than men during submaximal exercise, but they also indicate that this greater fat oxidation is shifted towards higher exercise intensities in women compared with men. References 1. Blaak E. Gender differences in fat metabolism. Curr Opin Clin Nutr Metab Care 4: 499-502, 2001. 2. Cheneviere X, Malatesta D, Peters EM, and Borrani F. A mathematical model to describe fat oxidation kinetics during graded exercise. Med Sci Sports Exerc 41: 1615-1625, 2009.

Effect of a 1-hour single bout of moderate-intensity exercise on fat oxidation kinetics.

The present study aimed to examine the effects of a prior 1-hour continuous exercise bout (CONT) at an intensity (Fat(max)) that elicits the maximal fat oxidation (MFO) on the fat oxidation kinetics during a subsequent submaximal incremental test (IncrC). Twenty moderately trained subjects (9 men and 11 women) performed a graded test on a treadmill (Incr), with 3-minute stages and 1-km.h(-1) increments. Fat oxidation was measured using indirect calorimetry and plotted as a function of exercise intensity. A mathematical model (SIN) including 3 independent variables (dilatation, symmetry, and translation) was used to characterize the shape of fat oxidation kinetics and to determine Fat(max) and MFO. On a second visit, the subjects performed CONT at Fat(max) followed by IncrC. After CONT performed at 57% +/- 3% (means +/- SE) maximal oxygen uptake (Vo(2max)), the respiratory exchange ratio during IncrC was lower at every stage compared with Incr (P < .05). Fat(max) (56.4% +/- 2.3% vs 51.5% +/- 2.4% Vo(2max), P = .013), MFO (0.50 +/- 0.03 vs 0.40 +/- 0.03 g.min(-1), P < .001), and fat oxidation rates from 35% to 70% Vo(2max) (P < .05) were significantly greater during IncrC compared with Incr. However, dilatation and translation were not significantly different (P > .05), whereas symmetry tended to be greater in IncrC (P = .096). This study showed that the prior 1-hour continuous moderate-intensity exercise bout increased Fat(max), MFO, and fat oxidation rates over a wide range of intensities during the postexercise incremental test. Moreover, the shape of the postexercise fat oxidation kinetics tended to have a rightward asymmetry.

The Escherichia coli RuvB branch migration protein forms double hexameric rings around DNA.

The RuvB protein is induced in Escherichia coli as part of the SOS response to DNA damage. It is required for genetic recombination and the postreplication repair of DNA. In vitro, the RuvB protein promotes the branch migration of Holliday junctions and has a DNA helicase activity in reactions that require ATP hydrolysis. We have used electron microscopy, image analysis, and three-dimensional reconstruction to show that the RuvB protein, in the presence of ATP, forms a dodecamer on double-stranded DNA in which two stacked hexameric rings encircle the DNA and are oriented in opposite directions with D6 symmetry. Although helicases are ubiquitous and essential for many aspects of DNA repair, replication, and transcription, three-dimensional reconstruction of a helicase has not yet been reported, to our knowledge. The structural arrangement that is seen may be common to other helicases, such as the simian virus 40 large tumor antigen.

Sequence homologies in the region preceding the transcription initiation site of the liver estrogen-responsive vitellogenin and apo-VLDLII genes.

In the liver of oviparous vertebrates vitellogenin gene expression is controlled by estrogen. The nucleotide sequence of the 5' flanking region of the Xenopus laevis vitellogenin genes A1, A2, B1 and B2 has been determined. These sequences have been compared to each other and to the equivalent region of the chicken vitellogenin II and apo-VLDLII genes which are also expressed in the liver in response to estrogen. The homology between the 5' flanking region of the Xenopus genes B1 and B2 is higher than between the corresponding regions of the other closely related genes A1 and A2. Four short blocks of sequence homology which are present at equivalent positions in the vitellogenin genes of both Xenopus laevis and chicken are characterized. A short sequence with two-fold rotational symmetry (GGTCANNNTGACC) was found at similar positions upstream of the five vitellogenin genes and is also present in two copies close to the 5' end of the chicken apo-VLDLII gene. The possible functional significance of this sequence, common to liver estrogen-responsive genes, is discussed.

Functional homogenization of bumblebee communities in alpine landscapes under projected climate change

Background: Bumblebees represent an active pollinator group in mountain regions and assure the pollination of many different plant species from low to high elevations. Plant-pollinator interactions are mediated by functional traits. Shift in bumblebee functional structure under climate change may impact plant-pollinator interactions in mountains. Here, we estimated bumblebee upward shift in elevation, community turnover, and change in functional structure under climate change. Method: We sampled bumblebee species at 149 sites along the elevation gradient. We used stacked species distribution models (S-SDMs) forecasted under three climate change scenarios (A2, A1B, RCP3PD) to model the potential distribution of the Bombus species. Furthermore, we used species proboscis length measurements to assess the functional change in bumblebee assemblages along the elevation gradient. Results: We found species-specific response of bumblebee species to climate change. Species differed in their predicted rate of range contraction and expansion. Losers were mainly species currently restricted to high elevation. Under the most severe climate change scenarios (A2), we found a homogenization of proboscis length structure in bumblebee communities along the elevation gradient through the upward colonization of high elevation by species with longer proboscides. Conclusions: Here, we show that in addition to causing the shift in the distribution of bumblebee species, climate change may impact the functional structure of communities. The colonization of high elevation areas by bumblebee species with long proboscides may modify the structure of plant-pollination interaction networks by increasing the diversity of pollination services at high elevation.