Intra-annual tracheid production in balsam fir stems and the effect of meteorological variables

Tracheid production of balsam fir in the Québec boreal forest (Canada) was studied by repeated cell analysis to investigate the influence of meteorological variables during the growing seasons 1998 to 2000. Wood micro-cores were extracted on a weekly basis throughout the growing season and sections were prepared in order to count the total number of cells produced. From the weekly cell number obtained, the rate of tracheid production was calculated and correlated with meteorological variables. The average total number of cells produced per year was reasonably uniform, increasing only from 36.6 in 1998, to 41.1 in 2000. However, different cell production rates were noted during the growing season. Regression analysis revealed that the cell production rate was largely dependent on minimum air and soil temperature during most of the cell production period. Mean and maximum temperature had less influence on cell production. Moreover, the influence of temperature was higher during earlywood production mainly from the end of May to mid-July. Lagging the weather data by 1-5 days decreased the relationship between temperature and cell production, showing the high correspondence with the same interval where cell production was measured. These results suggest a fast response of the cambium to temperature variation during tree-ring formation

Cellular phenology of annual ring formation of Abies balsamea in the Quebec boreal forest (Canada)

Cell formation in growth rings of balsam fir (Abies balsamea (L.) Mill) in the boreal forest was studied to describe the timing of ring formation and the development patterns of earlywood and latewood. Wood micro-cores were extracted during the growing season from 1998 to 2000. The micro-cores were stained with cresyl fast violet to facilitate counting the number of cells in the radial enlargement, wall thickening phases, and mature cell phases. The periods required to complete these various phases were then estimated. Variations in the beginning of the growing season (May 7 - June 7), the earlywood-latewood transition (July 2 - July 19), and the end of the growing season (August 20 - September 20) were observed. Short cell enlargement durations of less than a week for earlywood and 5-10 days for latewood were observed. Time required for cell wall thickening was about 20 days for earlywood and longer than 10-15 days for latewood. A certain flexibility was observed in the ring formation patterns and in the cell development rate, providing an advantage in the boreal forest where optimal growth conditions change from year to year. These findings on the spatial and temporal patterns of ring development may be useful for understanding tree relationships with climate or other environmental parameters. La formation des cellules dans les cernes annuels du sapin baumier (Abies balsamea (L.) Mill.) en forêt boréale a été étudiée pour décrire la chronologie de la formation des cernes et le développement du bois initial et final. Des micro-carottes ont été extraites pendant les saisons 1998 à 2000. Des sections ont été colorées à l'aide du « cresyl fast violet » pour faciliter le dénombrement des cellules dans les phases d'accroissement radial, de formation des parois secondaires et les cellules matures. Le temps requis pour que les cellules pour complètent ces phases a été estimé. Des variations dans le début de la croissance (7 mai au 7 juin), dans la transition du bois initial au bois final (2 juillet au 19 juillet) et dans la fin de la croissance (20 août au 20 septembre) ont été observées. De courtes périodes d'accrois sement, de moins d'une semaine pour le bois initial et de 5 à 10 jours pour le bois final ont été observées. Le temps nécessaire à l'épais sissement des parois secondaires était d'environ 20 jours pour le bois initial et plus de 30 à 35 jours pour le bois final respectivement. Les résultats mettent en évidence une certaine flexibilité dans le développement des cernes, ce qui procure un avantage en forêt boréale où les conditions optimales de croissance changent d'années en années. Ces résultats pourront être utiles pour mieux comprendre la relation entre les arbres et le climat ou d'autres paramètres environnementaux

Multi-scale influence of snowmelt on xylogenesis of black spruce

Snowmelt is considered to affect growth of the boreal forest. So, we tested the hypothesis that late snowmelts delay the onset of xylogenesis and reduce xylem production in trees. Timings of xylem formation were compared to the dates of complete snowmelt combining a 7-year monitoring of cambial activity with meteorological records in four plots of Picea mariana in Quebec, Canada. The spatial and temporal variability in snowfall was analyzed separately, so taking into account both the long- and short-term effects. Snowfall occurred from October to May, with a snow cover lasting 173-199 days. Overall, xylogenesis lasted 99-117 days, with onsets ranging from late May to mid-June. The highest cell productions were observed in the warmest site, where the longest periods of growth were observed. Although at long-term the effects of snowmelt were significant for both onset and duration of xylogenesis and cell production, at short-term only the relationship between the onset of xylogenesis and the date of complete snowmelt was significant. The initial hypothesis could be confirmed only partially. The different responses to the long- and short-term analyses demonstrate the multi-scale influence of snowfall on tree growth and the determinant role of nutrient cycling in the productivity of boreal ecosystems

Causes and correlations in cambium phenology: towards an integrated framework of xylogenesis

Although habitually considered as a whole, xylogenesis is a complex process of division and maturation of a pool of cells where the relationship between the phenological phases generating such a growth pattern remains essentially unknown. This study investigated the causal relationships in cambium phenology of black spruce [Picea mariana (Mill.) BSP] monitored for 8 years on four sites of the boreal forest of Quebec, Canada. The dependency links connecting the timing of xylem cell differentiation and cell production were defined and the resulting causal model was analysed with d-sep tests and generalized mixed models with repeated measurements, and tested with Fisher’s C statistics to determine whether and how causality propagates through the measured variables. The higher correlations were observed between the dates of emergence of the first developing cells and between the ending of the differentiation phases, while the number of cells was significantly correlated with all phenological phases. The model with eight dependency links was statistically valid for explaining the causes and correlations between the dynamics of cambium phenology. Causal modelling suggested that the phenological phases involved in xylogenesis are closely interconnected by complex relationships of cause and effect, with the onset of cell differentiation being the main factor directly or indirectly triggering all successive phases of xylem maturation

Sciences Sociales et cancérologie en France : vingt-cinq ans pour se faire entendre

Nous sommes en 1980, en France. Richard Doll et Ricard Peto viennent de publier leur célèbre ouvrage « The causes of Cancer », où ces deux éminents épidémiologistes concluent que près de 80 % des cancers seraient dus à des facteurs environnementaux, lies au mode de vie (y compris alimentaire). Dans le monde anglo-saxon, cela fait plusieurs années que des chercheurs s’intéressent aux « modes de vie », et certains biologistes ou cliniciens tentent des approches proches des sciences sociales pou..

Expression in E. coli and characterization of the catalytic domain of Botrytis cinerea chitin synthase

<p>Abstract</p> <p>Background</p> <p>Chitin synthase 3a (CHS3a) from <it>Botrytis cinerea </it>(Bc) catalyses the multiple transfer of <it>N</it>-acetylglucosamine (GlcNAc) residues to the growing chitin chain. Chitin, a β-1,4 linked GlcNAc homopolymer, is an essential cell wall component of filamentous fungi. Chitin synthase, processive membranous protein, has been recognized as a promising target for new antifungicides. Enzymatic characterizations of chitin synthases have been limited, mainly because purity and amounts of integral enzyme obtained after purification procedures have not been sufficient.</p> <p>Findings</p> <p>We undertook the preparation of two BcCHS3a fragment proteins, containing only the central domain and devoid of the N-terminal and transmembrane C-terminal regions. The central domain of CHS3a, named SGC (Spsa GntI Core), is conserved in all UDP-glycosyltransferases and it is believed to contain the active site of the enzyme. CHS3a-SGC protein was totally expressed as inclusion bodies in <it>Escherichia coli</it>. We performed recombinant CHS3a-SGC purification in denaturing conditions, followed by a refolding step. Although circular dichroism spectra clearly exhibited secondary structures of renatured CHS3a-SGC, no chitin synthase activity was detected. Nevertheless CHS3a-SGC proteins show specific binding for the substrate UDP-GlcNAc with a dissociation constant similar to the Michaelis constant and a major contribution of the uracil moiety for recognition was confirmed.</p> <p>Conclusions</p> <p>Milligram-scale quantities of CHS3a-SGC protein with native-like properties such as specific substrate UDP-GlcNAc binding could be easily obtained. These results are encouraging for subsequent heterologous expression of full-length CHS3a.</p

Raphaële Garreta, Des simples à l’essentiel

Cet ouvrage au titre évocateur est une étude exhaustive et passionnante de la relation complexe qui lie les hommes, leur environnement et leurs plantes médicinales. En effet, en dehors de l’engouement actuel pour « les plantes », ce livre, avec une approche anthropologique rigoureuse, nous conduit dans l’univers des cueilleurs, producteurs et utilisateurs de « simples » en France depuis un siècle et demi. On débute par une mise au point historique sur ce qui fut un personnage central dans la ..

Raphaële Garreta, Des simples à l’essentiel

Cet ouvrage au titre évocateur est une étude exhaustive et passionnante de la relation complexe qui lie les hommes, leur environnement et leurs plantes médicinales. En effet, en dehors de l’engouement actuel pour « les plantes », ce livre, avec une approche anthropologique rigoureuse, nous conduit dans l’univers des cueilleurs, producteurs et utilisateurs de « simples » en France depuis un siècle et demi. On débute par une mise au point historique sur ce qui fut un personnage central dans la ..