Éditeur(s) : HAL CCSD
Résumé : For their survival, plants need to grow in height to access light resource while ensuring their mechanical stability. Growth in height amplifies the mechanical constraints due to wind and gravity. Nevertheless these constraints represent morphogenetic signals that plants respond to by modifying their growth. There are two regulatory processes of growth by mechanical signals: thigmomorphogenesis and gravitropism. Thigmomorphogenesis expresses by a reduction of growth in height and an increase of growth in girth under the effect of mechanical signals. This is a way for plants to grow with controlling slenderness of their axes to avoid buckling (beating down). In some cases (storm, sudden exposure to a new mechanical environment) this process is not sufficient to prevent buckling, gravitropism then acts to restore axes orientation in case of no lethal buckling. With measuring several traits, we have demonstrated that these processes have a fundamental ecological role in the control of tree habit and the vertical structuration of ecosystems. As studies of climate changes seem to predict a higher frequency of storms it is important to study the diversity of their efficiency.
Colloque Adaptation au Changement Climatique de l'Agriculture et des Ecosystèmes

hal-00797377
https://hal.archives-ouvertes.fr/hal-00797377

Éditeur(s) : HAL CCSD Springer Verlag (Germany)
Résumé : In this paper we study merosity in the genus Urospatha within the framework of a resolved phylogeny of the Araceae. We analyse how a transition from dimerous or tetramerous merosity to pentamerous or hexamerous merosity can occur developmentally in the Lasioideae. In Urospatha, initiation of floral primordia along the inflorescence is acropetal, while development of flowers is basipetal. This indicates the presence of two distinct phases in the development of the Urospatha inflorescence. The first phase corresponds to initiation of flowers and establishment of the phyllotactic pattern, and the second phase to differentiation of floral organs. Urospatha is characterized by the presence of trimerous, tetramerous, pentamerous and rarely hexamerous flowers. In all types of flowers, the stamens are closely associated and opposite to the tepals. Pentamerous flowers are formed by addition of a sector comprising a stamen and tepal. Likewise, in the case of hexamerous flowers, two sectors are added. In the Lasioideae, the increase in the number of tepals and stamens is linked with two developmental processes that have appeared independently in the subfamily: (1) addition of one or two stamen-petal sectors (Anaphyllopsis and Urospatha), and (2) independent increase in the number of tepals and stamens on whorls, more or less organized and inserted in alternate position (Dracontium). Tetramerous whorls as they occur in basal Lasioideae would be homologous to two dimerous whorls from an evolutionary point of view.
ISSN: 0378-2697

hal-01019867
https://hal.archives-ouvertes.fr/hal-01019867
DOI : 10.1007/s00606-011-0475-6