Les séminaires ont lieu sur le Campus Montpellier SupAgro/INRA de La Gaillarde (2, place P. Viala Montpellier)
Jeudi 12 mai 2011
Amphi 208 (Cœur d’Ecole) à 14h
Auxin homeostasis in plants: How can a cell handle auxin?
Institute of Experimental Botany, Academy of Sciences of the Czech Republic-Prague
Plant hormone auxin and its asymmetrical distribution within cells, tissues and organs control various growth and developmental processes in plants. A guided movement of auxin along plant body underlies spatial and temporal coordination of these physiological events. Generally, two basic processes – i.e. auxin metabolism and auxin transport – are involved in regulation of auxin levels (and auxin homeostasis) in cells and their compartments. Auxin transport machinery consists of a sophisticated system of passive diffusion into cells of non-dissociated auxin molecules, as well as of activities of auxin transporters (influx and efflux carriers). For physical-chemical reasons, the activity and subcellular localization of auxin efflux carriers determine both quantity and direction of auxin flow, respectively. In Arabidopsis thaliana, two main protein families of auxin exporters are known – plant-specific PIN-FORMED proteins (PINs) and multidrug-resistance-like P-glycoprotein transporters of B-type of the ABC-superfamily (MDR/PGP/ABCBs), as well as one family for auxin importers (influx carriers) – permease-like AUX1/LAX proteins. Moreover, auxin transporters can facilitate not only intercellular but also intracellular auxin flow, and they undergo fine regulation on many levels, including feed-back regulation of intracellular auxin content by auxin itself. Quantitative characterization of auxin transport in suspension-grown tobacco BY-2 cells (Nicotiana tabacum L., cv. Bright-Yellow 2) was performed using various auxins and their structurally-related analogues. Results pointed to the preferential affinity of the auxin transport machinery to those compounds which were able to induce DR5rev::GFP reporter and which showed other auxin-like physiological properties. On the basis of data obtained by auxin-accumulation assays and metabolic profiling in BY-2 cells, a preliminary version of mathematical model of auxin movement was designed; such model has a potential to complement the already existing models of auxin flow on the tissue and organ levels, and to point to so far unknown components and processes involved.
Contact : Philippe Nacry