DEVELOPMENTAL-CHANGES IN THE 2-DIMENSIONAL PROTEIN PATTERN OF PLASMA-MEMBRANE VESICLES BETWEEN SINK AND SOURCE LEAVES FROM SUGAR-BEET

Young heterotrophic leaves are believed to import assimilates via the symplast, while in many species, including sugar beet (Beta vulgaris L .), mature autotrophic leaves seem to export assimilates via the apopl ast. This dramatic change in transport physiology is expected to be ac companied by important changes in the polypeptide pattern of the plasm a membrane. Immobilized pH gradients in the first dimension and SDS-po lyacrylamide gel electrophoresis in the second dimension were used to compare plasma membrane proteins from sink and source leaves by two di mensional gel electrophoresis. The analysis allows a high resolution s eparation of plant plasma membrane proteins and reveals that the overa ll pattern is very similar between both situations. However a set of n ew polypeptides occurs concomitantly with the gain in active sucrose t ransport capacity in mature leaves in a size range between 30 and 55 k Da. The possibility that some of these polypeptides possess transport activity is discussed.