Recherches sur la croissance des bourgeons de chêne et de quelques autres espèces ligneuses

International audienc

Etude biologique et biochimique du determinisme de la croissance rythmique du chene pedoncule (Quercus robur L.). Effets de l'ablation des feuilles

National audienc

Étude biologique et biochimique du déterminisme de la croissance rythmique du chêne pédonculé (Quercus robur L). Effets de l'ablation des feuilles

La croissance du chêne pédonculé cultivé à 25°C (± 1 °C) en jour long, est parfaitement rythmique. La suppression des limbes dont la taille est inférieure à 10 mm, la transforme en croissance continue. La suppression des feuilles d'un étage n ayant atteint leur taille définitive, provoque une très forte réduction en longueur de l'étage n + 1 lorsque celui-ci se développe. Au cours d'un flush, l'incorporation de la 14C-DMO (5-5' diméthyloxazolidine 2-4 dione), acide faible lipophile, par le bourgeon terminal, les tissus de l'axe sous-jacent au bourgeon terminal et les feuilles en croissance varie au cours du temps chez une plante intacte. Les résultats obtenus avec la fourniture de 14CO 2 au cours de la troisième vague de croissance confirment les résultats obtenus avec la 14C-DMO. Dans le cas d'une plante dont la croissance est devenue continue à la suite de l'ablation des très jeunes feuilles, le bourgeon accumule toujours plus de 14C-DMO que les entre-nœuds. Dans le cas de plantes où seule la croissance en longueur de l'étage est réduite par ablation des feuilles ayant atteint leur taille définitive, l'absorption de la 14C-DMO est identique à celle des témoins. L'ensemble des résultats permet de proposer une hypothèse explicative de la croissance rythmique du chêne pédonculé, basée sur la notion de puits.A biological and biochemical study of the factors determining rhythmical growth In pedunculate oak (Quercus robur). The effects of leaf removal. Quercus robur L showed perfect rhythmical growth when it was cultivated under controlled conditions at 25°C (± 1 °C), with long days or continuous light at 80 μmol·m-2·s-1. It was characterized by a regular succession of flushes. One flush lasted for 3 weeks: the first 2 weeks were the growing period and the last was the rest period. It was a false rest period because the activity of the apical meristem did not stop. A flush was characterized by the succession of scales and leaves, and by a succession of long and short internodes. The rhythmical growth is inhibited when 10 mm leaves are removed. Then continuous growth takes place. The apical meristem keeps producing a primortium. If a primortium is not removed it always gives a leaf and never a scale. The removal of the leaves of a flush at their adult size produces a strong reduction in the length of the next flush. During a flush, the intracellular concentration of the 14C-DMO (5 dimethyl oxazolidine 2-4 dione), a weak and lipophylacid, in the terminal bud and in itsadjacent axial tissues, and in leaves, varies in an untouched plant. The same variations are repeated for every flush. The results with a supply of 14CO2 confirm the results with the 14C-DMO. In the case of plants with continuous growth caused by the regular removal of young leaves, the intracellular concentration of 14C-DMO always remains higher in the terminal bud than in the internodes. There is no change in plants where only the adult leaves of a flush are removed. Our results allow us to put forward a nutritional hypothesis of the rhythmical growth of Quercus robur L. The rhythmical growth is the result of the relationships between 3 elements which are: the apical meristem, the axial tissues bearing the terminal bud, and the very young leaves. If one element, the axial tissues or the young leaves becomes stronger than the others, the growth is changed. Then it is possible that the internodes become short and the primordium produces scales

Impact of mindfulness on the neural responses to emotional pictures in experienced and beginner meditators

There is mounting evidence that mindfulness meditation is beneficial for the treatment of mood and anxiety disorders, yet little is known regarding the neural mechanisms through which mindfulness modulates emotional responses. Thus, a central objective of this functional magnetic resonance imaging study was to investigate the effects of mindfulness on the neural responses to emotionally laden stimuli. Another major goal of this study was to examine the impact of the extent of mindfulness training on the brain mechanisms supporting the processing of emotional stimuli. Twelve experienced (with over 1000 h of practice) and 10 beginner meditators were scanned as they viewed negative, positive, and neutral pictures in a mindful state and a non-mindful state of awareness. Results indicated that the Mindful condition attenuated emotional intensity perceived from pictures, while brain imaging data suggested that this effect was achieved through distinct neural mechanisms for each group of participants. For experienced meditators compared with beginners, mindfulness induced a deactivation of default mode network areas (medial prefrontal and posterior cingulate cortices) across all valence categories and did not influence responses in brain regions involved in emotional reactivity during emotional processing. On the other hand, for beginners relative to experienced meditators, mindfulness induced a down-regulation of the left amygdala during emotional processing. These findings suggest that the long-term practice of mindfulness leads to emotional stability by promoting acceptance of emotional states and enhanced present-moment awareness, rather than by eliciting control over low-level affective cerebral systems from higher-order cortical brain regions. These results have implications for affect-related psychological disorders