The water relations of two tropical rainforest species (Virola surinamensis and Eperua falcata): Is Virola unusual as previously reported?

HYDROInternational audienceThe objective of this study was to examine the water relations and hydraulic architecture and vulnerability to cavitation in Virola surinamensis and V. michelii and to compare to similar measurements in Eperua falcata. In several previous reports Virola was seen to have a rather narrow range of xylem pressure potentials (Ψx) near zero in the course of a wet-season day while having water fluxes quite close to Eperua. We tested the hypothesis that the narrow range of Ψx might be consistent with very high hydraulic conductivities of stems, roots and shoots and high vulnerability to cavitation in Virola compared to Eperua. When this hypothesis proved false we concluded that the previous determinations of Ψx might be wrong in Virola due to latex. We re-examined the determination of Ψx in Virola by the pressure chamber technique and compared results to determination of Ψleaf by the thermocouple psychrometer technique and found that the likely range of Ψx are more negative than previously reported. Problems concerning the determination of Ψx in species with latex are discussed

In vitro mycorrhization of micropropagated plants: studies on Castanea sativa Mill.

In vitro mycorrhization can be made by several axenic and nonaxenic techniques but criticism exists about their artificiality and inability to reproduce under natural conditions. However, artificial mycorrhization under controlled conditions can provide important information about the physiology of symbiosis. Micropropagated Castanea sativa plants were inoculated with the mycorrhizal fungus Pisolithus tinctorius after in vitro rooting. The mycorrhizal process was monitored at regular intervals in order to evaluate the mantle and hartig net formation, and the growth rates of mycorrhizal and nonmycorrhizal plants. Plant roots show fungal hyphae adhesion at the surface after 24 hours of mycorrhizal induction. After 20 days a mantle can be observed and a hartig net is forming although the morphology of the epidermal cells remains unaltered. At 30 days of root–fungus contact the hartig net is well developed and the epidermal cells are already enlarged. After 50 days of mycorrhizal induction, growth was higher for mycorrhizal plants than for nonmycorrhizal ones. The length of the major roots was lower in mycorrhizal plants after 40 days. Fresh and dry weights were higher in mycorrhizal plants after 30 days. The growth rates of chestnut mycorrhizal plants are in agreement with the morphological development of the mycorrhizal structures observed at each mycorrhizal time. The assessment of symbiotic establishment takes into account the formation of a mantle and a hartig net that were already developed at 30 days, when differences between fresh and dry weights of mycorrhizal and nonmycorrhizal plants can be quantified. In vitro conditions, mycorrhization influences plant physiology after 20 days of root–fungus contact, namely in terms of growth rates. Fresh and dry weights, heights, stem diameter and growth rates increased while major root growth rate decreased in mycorrhizal plants.Springe

Uniform Selection as a Primary Force Reducing Population Genetic Differentiation of Cavitation Resistance across a Species Range

Background: Cavitation resistance to water stress-induced embolism determines plant survival during drought. This adaptive trait has been described as highly variable in a wide range of tree species, but little is known about the extent of genetic and phenotypic variability within species. This information is essential to our understanding of the evolutionary forces that have shaped this trait, and for evaluation of its inclusion in breeding programs. Methodology: We assessed cavitation resistance (P 50), growth and carbon isotope composition in six Pinus pinaster populations in a provenance and progeny trial. We estimated the heritability of cavitation resistance and compared the distribution of neutral markers (FST) and quantitative genetic differentiation (QST), for retrospective identification of the evolutionary forces acting on these traits. Results/Discussion: In contrast to growth and carbon isotope composition, no population differentiation was found for cavitation resistance. Heritability was higher than for the other traits, with a low additive genetic variance (h 2 ns = 0.4360.18, CVA = 4.4%). QST was significantly lower than FST, indicating uniform selection for P50, rather than genetic drift. Putativ

Basal ganglia dysfunction in OCD: subthalamic neuronal activity correlates with symptoms severity and predicts high-frequency stimulation efficacy

Functional and connectivity changes in corticostriatal systems have been reported in the brains of patients with obsessive–compulsive disorder (OCD); however, the relationship between basal ganglia activity and OCD severity has never been adequately established. We recently showed that deep brain stimulation of the subthalamic nucleus (STN), a central basal ganglia nucleus, improves OCD. Here, single-unit subthalamic neuronal activity was analysed in 12 OCD patients, in relation to the severity of obsessions and compulsions and response to STN stimulation, and compared with that obtained in 12 patients with Parkinson's disease (PD). STN neurons in OCD patients had lower discharge frequency than those in PD patients, with a similar proportion of burst-type activity (69 vs 67%). Oscillatory activity was present in 46 and 68% of neurons in OCD and PD patients, respectively, predominantly in the low-frequency band (1–8 Hz). In OCD patients, the bursty and oscillatory subthalamic neuronal activity was mainly located in the associative–limbic part. Both OCD severity and clinical improvement following STN stimulation were related to the STN neuronal activity. In patients with the most severe OCD, STN neurons exhibited bursts with shorter duration and interburst interval, but higher intraburst frequency, and more oscillations in the low-frequency bands. In patients with best clinical outcome with STN stimulation, STN neurons displayed higher mean discharge, burst and intraburst frequencies, and lower interburst interval. These findings are consistent with the hypothesis of a dysfunction in the associative–limbic subdivision of the basal ganglia circuitry in OCD's pathophysiology

Parkinson’s disease mouse models in translational research

Animal models with high predictive power are a prerequisite for translational research. The closer the similarity of a model to Parkinson’s disease (PD), the higher is the predictive value for clinical trials. An ideal PD model should present behavioral signs and pathology that resemble the human disease. The increasing understanding of PD stratification and etiology, however, complicates the choice of adequate animal models for preclinical studies. An ultimate mouse model, relevant to address all PD-related questions, is yet to be developed. However, many of the existing models are useful in answering specific questions. An appropriate model should be chosen after considering both the context of the research and the model properties. This review addresses the validity, strengths, and limitations of current PD mouse models for translational research

The effects of ectomycorrhizal status on carbon dioxide assimilation capacity, water-use efficiency and response to transplanting in seedlings of Pseudotsuga menziesii (Mirb) Franco

One year-old Douglas fir seedlings, mycorrhizal with Laccaria laccata or with Thelephora terrestris and grown at two levels of phosphorus in the nutrient solution (10 and 40 mg·l-1 P), were compared for water relations and gas exchange before and after transplanting in non-limiting water conditions. The results show that i), L laccata is more efficient than T terrestris in increasing photosynthesis and water use efficiency, ii), phosphorus deficiency reduces photosynthesis and water use efficiency, iii), the stimulating effect of L laccata on photosynthesis and water use efficiency is, at least partly, due to the improvement of phosphorus nutrition, iv), the photosynthesis reduction resulting from transplanting is due to a non-stomatal mechanism, and v), the recovery of photosynthesis involves the regrowth of the external mycelium of mycorrhizas. These results are discussed from the viewpoint of the plant-fungus relationships.Effets du statut mycorhizien sur la capacité d'assimilation de CO2, l'efficience d'utilisation de l'eau et la réponse à la transplantation de semis de Pseudotsuga menziesii (Mirb) Franco. Des semis de 1 an de douglas, mycorhizés par Laccaria laccata ou Thelephora terrestris ont été élevés durant une saison de croissance à 2 niveaux de phosphore dans la solution nutritive (10 et 40 mg·l-1 P) et ont été comparés du point de vue des relations hydriques et des échanges gazeux avant et après transplantation (à 2 dates différentes, en octobre et en février) en conditions hydriques non limitantes. A faible niveau de phosphore, les plants inoculés par L laccata avaient une surface foliaire plus importante que les plants mycorhizés par T terrestris (tableau 1) et étaient également caractérisés par des taux d'assimilation de CO2 et d'efficience photosynthétique d'utilisation de l'eau plus élevés (tableau II et fig 1). La carence en phosphore réduit la photosynthèse et l'efficience d'utilisation de l'eau (tableau II, fig 1). L'effet stimulant de L laccata sur l'efficience de l'eau est dû, au moins en partie, à l'amélioration de la nutrition en phosphore (fig 7 et 9).La réduction de la photosynthèse consécutive à la transplantation (fig 2), bien qu'accompagnée par une fermeture stomatique (fig 3), est dûe essentiellement à un mécanisme non stomatique (fig 4) et n'est pas liée à une altération de l'état hydrique et nutritionel (fig 7 et 8) des plants. Le rétablissement de la photosynthèse après transplantation est concomitant à la régénération racinaire (fig 5), mais son déterminisme implique également la reprise d'activité du champignon (fig 6). Ces résultats sont discutés du point de vue des relations plante-champignon

Changes in carbon uptake and allocation patterns in Quercus robur seedlings in response to elevated CO2 and water stress: an evaluation with 13C labelling

A semi-closed 13CO2 labelling system (1.5% 13C) was used to assess both carbon uptake and allocation within pedunculate oak seedlings (Quercus robur L) grown under ambient (350 vpm) and elevated (700 vpm) atmospheric CO2 concentration ([CO2]) and in either well-watered or droughted conditions. Pulse-chase 13C labelling data highlighted the direct positive effect of elevated CO2 on photosynthetic carbon acquisition. Consequently, in well-watered conditions, CO2enriched plants produced 1.52 times more biomass (dry mass at harvest) and 1.33 times more dry root matter (coarse plus fine roots) over the 22-week growing period than plants grown under ambient [CO 2]. The root/shoot biomass ratio was decreased both by drought and [CO 2], despite lower N concentrations in CO2-enriched plants. However, both long-term and short-term C allocation to fine roots were not altered by CO2. and relative specific allocation (RSA), a parameter expressing sink strength, was higher in all plant organs under 700 vpm compared to 350 vpm. Results showed that C availability for growth and metabolic processes was greater in fine roots of oaks grown under an elevated CO 2 atmosphere irrespective of soil water availability.Effets de l'augmentation de la concentration atmosphérique en CO2 et de la sécheresse sur l'assimilation et la redistribution du carbone de plants de Quercus robur : une approche par marquage 13C. Un système semi-fermé de marquage isotopique par 13CO2 (1,5 % 13C) a été utilisé pour évaluer l'assimilation et la répartition du carbone pour des plants de chêne (Quercus robur L) élevés sous une concentration atmosphérique en CO2 ([CO2]) ambiante (350 vpm) ou élévée (700 vpm) et en conditions d'alimentation hydrique optimale ou limitante. Les résultats obtenus à partir de cinétiques de charge-redistribution de 13C montrent un effet direct de l'augmentation de [CO2] sur l'acquisition photosynthétique de carbone. En conditions d'alimentation hydrique optimale, la biomasse totale des plants croissant sous [CO2] élevée a été multipliée par 1,52 (matière sèche à la fin de la période de croissance de 22 semaines) comparativement au plants croissant sous [CO 2] ambiante, cependant que la matière sèche des racines (racines fines et grosses) était multipliée par 1,33. Le rapport biomasse racinaire/biomasse aérienne des plants était diminué à la fois par la sécheresse et par l'augmentation de [CO 2], en dépit de concentrations tissulaires en N plus faibles dans les plants croissant en conditions de [CO2] élevée. Toutefois, l'allocation de carbone aux fines racines (diamètre < 2 mm), considérée soit de façon intégrée dans le temps (accumulation de biomasse), soit à court terme (données issues des marquages isotopiques), n'était pas affectée par la [CO2]. Le taux d'allocation spécifique de carbone (RSA), un paramètre exprimant la force des puits de carbone, était plus élevé à 700 vpm qu'à 350 vpm pour l'ensemble des compartiments des plants. Les résultats font ressortir une augmentation de la disponibilité en C pour la croissance et le métabolisme dans les fines racines en relation avec l'augmentation de [CO2] et indépendamment des disponibilités hydriques dans le sol

Osmotic adjustment in sessile oak seedlings in response to drought

Three-year-old sessile oak seedlings were submitted to drought developed at two different rates (0.050 and 0.013 MPa·day-1). Drought was controlled by combining levels of irrigation and grass competition. At the end of summer, predawn leaf water potential reached values of -2.3 and -0.8 MPa in the rapid and slow rates of drought development, respectively, and leaf osmotic potential at full turgor reached values of -2.0 and -1.5 MPa, for the same treatments. For both treatments, leaf water potential and leaf osmotic potential were linearly and positively correlated. The rapid rate of drought development resulted in a greater degree of osmotic adjustment (0.45 versus 0.34 MPa·MPa-1).Effets d'une sécheresse édaphique sur l'ajustement osmotique de jeunes plants de chêne. Des plants de chêne aessile âgés de 3 ans ont été soumis à des déficits hydriques se développant à deux vitesses (0,050 et 0,013 MPa·jour-1), obtenus en croisant deux niveaux d'irrigation et de compétition herbacée. À la fin de l'été, le potentiel hydrique foliaire de base était de — 2,3 et -0,8 MPa sous dessèchement rapide et sous dessèchement lent, respectivement. Le potentiel osmotique foliaire à pleine turgescence était de — 2,0 et — 1,5 MPa dans les mêmes traitements. Dans les deux traitements, le potentiel hydrique de base et le potentiel osmotique étaient linéairement et positivement corrélés. Le dessèchement rapide a induit un degré d'ajustement osmotique plus important (0,45 contre 0,34 MPa·MPa-1 sous dessèchement lent)

Growth dynamics, transpiration and water-use efficiency in Quercus robur plants submitted to elevated CO 2

Seedlings of pedunculate oak (Quercus robur L) were grown for one growing season under ambient (350 μmol mol-1) and elevated (700 μmol mol-1) atmospheric CO2 concentration ([CO2]) either in well-watered or in droughted (the water supply was 40% of the well-watered plants transpiration in both [CO2]) conditions. In the droughted conditions, gravimetric soil water content (SWC) was on average 4 10 -2 g g-1 lower under elevated [CO2]. In well-watered conditions, biomass growth was 39% higher in the elevated [CO2] treatment than under ambient [CO 2]. However relative growth rate (RGR) was stimulated by the elevated [CO2] only for 17 days, in July, at the end of the stem elongation phase (third growing flush), which corresponded also to the phase of maximum leaf expansion rate. Both the number of leaves per plant and the plant leaf area were 30% higher in the elevated [CO2] treatment than under ambient [CO2]. In the droughted conditions, no significant enhancement in biomass growth and in plant leaf area was brought about by the elevated [CO2]. Transpiration rate was lower in the elevated [CO2] conditions, but whole plant water use was similar in the two [CO2] treatments, reflecting a compensation between leaf area and stomatal control of transpiration. Transpiration efficiency (W = biomass accumulation/plant water use) was improved by 47% by the elevated [CO2] in well-watered conditions but only by 18% in the droughted conditions. Carbon isotope discrimination (Δ) was decreased by drought and was increased by the elevated [CO2]. A negative linear relationship was found between transpiration efficiency divided by the atmospheric [CO2] and Δ, as predicted by theory.Dynamique de croissance, transpiration et efficience d'utilisation de l'eau de plants de Quercus robursoumis à une concentration élevée en CO2 et à la sécheresse. Des semis de chêne pédonculé (Quercus robur L) ont été soumis, durant leur première saison de végétation, à des concentrations atmosphériques en CO2 ([CO2]) ambiantes (350 μmol mol-1) ou doublées (700 μmol mol-1) en conditions de bonne alimentation hydrique ou de sécheresse (fourniture d'eau égale à 40 % de la transpiration des plants bien irrigués pour chacune des conditions de [CO2]). L'humidité pondérale du sol (SWC) était en moyenne inférieure de 4 10-2 g g-1 sous [CO 2] élevé comparativement à la [CO 2] ambiante. En conditions hydriques favorables, l'augmentation de la concentration en CO2 est à l'origine d'une stimulation de la croissance de 39 %. Cependant le taux de croissance relative (RGR) n'est stimulé par l'augmentation de la concentration en CO2 qu'au cours d'un intervalle de temps de 17 jours, en juillet, correspondant à la fin de la phase d'élongation de la tige (troisième flush de croissance) et à la phase de vitesse d'expansion foliaire maximale. Le nombre de feuilles ainsi que la surface foliaire par plant sont augmentés de 30 % par l'augmentation de la concentration en CO2. En conditions de sécheresse, aucune stimulation de croissance pondérale ni de surface foliaire par plant ne sont observées en réponse à l'augmentation de la concentration atmosphérique en CO2. Le taux de transpiration est réduit par l'augmentation de la concentration en CO2, mais la transpiration totale par plant n'est pas affectée par la concentration atmosphérique en CO2, traduisant une compensation entre augmentation de surface foliaire et fermeture stomatique. L'efficience de transpiration (W = accumulation de biomasse/eau transpirée) est augmentée de 47 % par l'augmentation de la concentration en CO2 en régime hydrique favorable et seulement de 18 % en régime hydrique limitant. La discrimination isotopique du carbone (Δ) des plants est diminuée par la sécheresse et augmentée par le doublement de la concentration en CO2. Une relation linéaire négative entre l'efficience de transpiration divisée par la concentration atmosphérique en CO2 et Δ est observée conformément à la théorie (équation 5)

The effects of elevated CO2 and water stress on whole plant CO2 exchange, carbon allocation and osmoregulation in oak seedlings

Seedlings of Quercus robur L grown under present (350 μmol mol -1) or twice the present (700 μmol mol-1) atmospheric CO2 concentrations, were either maintained well-watered or subjected to a drought constraint late in the growing season (25 August 1993). Despite an initial stimulation of biomass growth (+44%) by elevated CO2, there was no significant difference in plant dry weight at the end of the growing season (15 October 1993) between the two CO2 treatments, irrespective of watering regime. Under drought conditions, although there was no growth increase in response to elevated CO2 concentration, there was a stimulation in net photosynthesis. In addition, the respiration rate of the root + soil system (root dry matter basis) was slightly lower in the elevated than in the ambient CO2 concentration. These results, together with the results from short-term 13C labelling, suggest enhanced plant carbon losses through processes not assessed here (aerial respiration, root exudation, etc) under elevated CO2 concentration. In the droughted conditions, new carbon relative specific allocation values (RSA) were greater under elevated CO2 than under ambient CO2 concentration in both leaf and root compartments. Osmotic potentials at full turgor (π o) were lowered in response to water stress in leaves by 0.4 MPa for the elevated CO2 treatment only. In roots, osmotic adjustment (0.3 MPa) occurred in both the CO2 treatments.Effets de l'augmentation de la concentration atmosphérique en CO2 et d'un déficit hydrique sur les échanges gazeux, la répartition carbonée et l'osmorégulation de semis de chêne. Des semis de chêne pédonculé (Quercus robur L) cultivés sous des concentrations atmosphériques en CO2 de 350 ou 700 μmol mol-1 ont été, pour moitié, soit bien alimentés en eau, soit soumis à une sécheresse appliquée tardivement dans la saison de végétation (25 août 1993). En dépit d'une première phase de stimulation de la production de biomasse (+44 %, 30 juillet 1993) par le CO2, aucune différence significative dans la biomasse des plants entre les deux traitements CO2 n'a été observée à la fin de la saison de végétation (15 octobre 1993), ceci quel que soit le régime hydrique. En conditions de sécheresse, l'assimilation nette de CO2 fut stimulée par le CO2, malgré l'absence de stimulation sur la croissance. Par ailleurs, le taux de respiration du système racine-sol (rapportée à la matière sèche racinaire) était légèrement plus faible sous CO2 élevé que sous CO2 ambiant. Ces résultats, ajoutés aux résultats de marquages 13CO2 à court terme suggèrent des pertes carbonées augmentées sous CO2 élevé, par l'intermédiaire de processus non étudiés ici (respiration aérienne, exudation racinaire,...). En conditions de sécheresse, les valeurs de répartition relative spécifique du nouveau carbone étaient plus importantes sous CO2 élevé que sous CO2 normal, à la fois dans les compartiments foliaire et racinaire. Les potentiels osmotiques à pleine turgescence (π0) étaient diminués en réponse au stress hydrique dans les feuilles de 0,4 MPa uniquement pour le traitement CO 2 à 700 μmol mol -1. Dans les racines, un ajustement osmotique (0,3 MPa) était observé pour les deux traitements CO 2