CHANGES IN THE 2-DIMENSIONAL PROTEIN PATTERN AND IN GENE-EXPRESSION DURING THE SINK-TO-SOURCE TRANSITION OF POTATO-TUBERS

During their development, potato tubers switch from import (sink stage ) to export (source stage) of carbohydrates, amino acids and other com pounds. Comparison of sink and source tubers on both RNA and protein l evels reveals drastic differences despite high morphological similarit y of the two stages. According to IPG-based 2D-PAGE, the protein patte rn of sink and source tubers from Solanum tuberosum cv. Berolina shows about 25% stage-specific spots for total protein and plasma membrane protein. In the plasma membrane, the major change is the appearance of a new set of proteins in the M(r) range of 30-55 kDa. Following the e xpression of individual genes such as those encoding patatin, which co ntributes up to 40% of the total soluble protein of developing tubers, at least 53 distinguishable spots are found in sink tubers. In the so urce situation, both the amount and number of patatin polypeptides are greatly reduced. Correspondingly, on the RNA level, patatin genes are almost exclusively expressed in sink tubers.