1. Department Lothar Willmitzer, Max Planck Institute of Molecular Plant Physiology, 14424 Potsdam, Germany, RIKILT (Institute of Food Safety), P.O. Box 230, 6700 AE Wageningen, The Netherlands and Plant Research International, P.O. Box 16, 6700 AA Wageningen, The Netherlands, Department of Material Chemistry, Kyoto University, PRESTO JST, Sakyo-ku, Kyoto 606-8501, Japan, and Department of Polymer Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan