Éditeur(s) : HAL CCSD
Résumé : Gravitropism is a major process in vertical growth as it allows the positioning of plant in the gravity field and thus, for trees, it takes part in the light foraging strategies. Without any gravitropism, trees would adopt a weeping habit or fall on the ground due to the increasing with growth supported weight, especially at the advance regeneration stage (sapling stage) in the understorey, where tree are very slender and poorly stiff. Most of the gravitropic studies are made by physiologists in order to understand the process and thus are associated to complex laboratory methods (genetic engineering, anatomical studies, accurate 2D ou 3D measurements of form changes with time). In order to study the ecological relevance and the specific diversity of gravitropic performances in natural forests, we developed a framework that uses different kinds of datas. Synchronical analysis has been done i) at the population level in large sample of trees and ii) at the tree level from destructive measurement of the dissymmetry maturation strains known to be the main motor of the posture control reaction of trees. In both cases, biomechanical models allows to estimate some aspects of the dynamic gravitropic process. Diachronical analysis has been done in natural conditions on permanent plots, or in a more traditional way, by observing in greenhouse experiments the righting movements of plants artificially tilted. In the first case, the problem is the high variability of natural disturbances and the slowness of growth and movements in the dark understorey. The second choice allows a measurement of a capacity (i.e. the ability of the species to react in quite extreme conditions of verticality disturbance but good for growth light and nutrient conditions) that is more easy to analyse, but is maybe not so relevant for estimating the ecological strategy (some species could have developed a high efficience of gravitropic reaction in natural conditions by avoiding the mechanical disturbance or adapting the reaction to slow growth and changing environments in natural conditions). All approaches use the same basic biomechanical modelling, i) to analyse simultaneously the reaction and the disturbance (due to the weight increase) during growth, or ii) to combine different parameters (geometry, growth, weight, maturation strains) involved in shape changes and posture control. They give a classification of the species according to their gravitropic performances. Results on 15 species are discussed, with relation to shade-tolerance or avoidance.
6th Plant Biomechanics Conference
Cayenne, France

hal-00565956
https://hal.archives-ouvertes.fr/hal-00565956

Éditeur(s) : HAL CCSD
Résumé : International audience
The Aegean domain is a key area for understanding the processes of back-arc extension. Observed deformation pattern and present day kinematics result from the interaction between the southward retreat of the Hellenic trench and the westward escape of Anatolia. Using laboratory experiments designed to study lithosphere-scale deformation, we show that the overall pattern of Aegean extension requires not only the combination of trench retreat and Anatolia escape since 15 Ma but also the presence of an inherited lithosphere-scale mechanical discontinuity: the Vardar Suture Zone (VSZ). The reactivation in dextral shear of the eastern branch of the VSZ accommodates both the trench retreat (NS stretching) and the westward escape of Anatolia (EW shortening) in the Cyclades area since 15 Ma. Additionally, our model shows that the North Anatolian Fault (NAF) is a late structure in the evolution of the Aegean, initiated 10 Ma after the onset of Anatolia escape. The model displays displacement sub-domains, which result from strain partitioning instead of being “rigid microplates”, directly comparable to the present-day displacement field (GPS) of the Aegean and western Anatolia. Our modelling provides a simple way to look at the dynamics of Aegean extension in two main stages. From middle Eocene to middle Miocene, extension was only driven by the southward retreat of the Hellenic trench at a rate lower than 1 cm.y-1. Since middle Miocene, the combination of slab rollback with Anatolia westward escape, resulted in a southwest direction of trench retreat, with an accelerating rate of up to 3 cm.y-1.
AGU Fall Meeting 2015
San Francisco, United States

insu-01242045
https://hal-insu.archives-ouvertes.fr/insu-01242045

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : Four new sesquiterpene alkaloids (1-4) with a β-dihydroagrofuran skeleton and a new triterpenoid (5) were isolated from an ethyl acetate extract of Maytenus oblongata stems. Their structures were elucidated using 1D and 2D NMR spectroscopy as well as MS and ECD experiments. The M. oblongata stem EtOAc extract and the pure compounds isolated were tested for larvicidal activity against Aedes aegypti under laboratory conditions, and compounds 2 and 3 were found to be active.
ISSN: 0163-3864

hal-01603411
https://hal.archives-ouvertes.fr/hal-01603411
DOI : 10.1021/acs.jnatprod.6b00850
PUBMED : 28186749
PRODINRA : 406747