Update on sucrose transport in higher plants

Sucrose as the major transported form of fixed carbon, must be translocated from the sites of synthesis, i.e. the green tissues, to the sites of consu mption and storage, i.e. the non-green cells and organs. For apoplasmic tra nsport, carrier-mediated processes are required at the plasma membrane. Fun ctional complementation of modified yeast strains has enabled the isolation and characterization of a large family of sucrose carriers (SUT) from a wi de variety of species. In Xenopus oocytes, electrophysiological methods dem onstrated that the SUTs function as proton co-transporters, Localization st udies show that at least SUT1 is present at the plasma membrane of enucleat ed sieve elements, indicating macromolecular transport of its mRNA or prote in from the companion cell to the sieve element. Inhibition of the transpor t activity in several transgenic plant species proves that SUT function is essential for long-distance transports Further experiments will be required to assign specific functions to the other members of the SUT family.