XVI International Botanical Congess

Most plants convert their fixed CO2 into sucrose, the main transport form for carbohydrates in the phloem. Sucrose is loaded into the phloem and distributed to various sinks tissues. Using phloem mobile fluorescent probes we were able to identify sinks that are symplastically connected to the phloem through plasmodesmata and symplastically isolated sinks. In the latter case, sucrose is unloaded into the apoplast from where it can be transported into the different sinks either directly or after hydrolyzis by extracellular invertases. Large families of mono- and disaccharide transporters catalyze this uptake of glucose and fructose or of sucrose. Symplastically isolated sinks possess one or several transporters in their plasma membranes. The expression of the genes encoding these transporters may be modulated in response to environmental stresses, such as wounding or infection, underlining the important role of these proteins in the regulation of assimilate fluxes throughout the plant.