POLYPHENOL OXIDASE IN POTATO - A MULTIGENE FAMILY THAT EXHIBITS DIFFERENTIAL EXPRESSION PATTERNS

Polyphenol oxidase (PPO) activity in potato (Solanum tuberosum) plants was high in stolons, tubers, roots, and flowers but low in leaves and stems. PPO activity per tuber continued to increase throughout tuber development but was highest on a fresh weight basis in developing tube rs. PPO activity was greatest at the tuber exterior, including the ski n and cortex tissue 1 to 2 mm beneath the skin. Flowers had high PPO a ctivity throughout development, particularly in the anthers and ovary. Five distinct cDNA clones encoding PPO were isolated from developing tuber RNA. POT32 was the major form expressed in tubers and was found in all parts of the tuber and at all stages of tuber development. It w as also expressed in roots but not in photosynthetic tissues. POT33 wa s expressed in tubers but mainly in the tissue near the skin. POT72 wa s detected in roots and at low levels in developing tubers. NOR333 was identical with the P2 PPO clone previously isolated from potato leave s (M.D. Hunt, N.T. Eannetta, Y. Haifeng, S.M. Newman, J.C. Steffens [1 993] Plant Mol Biol 21:59-68) and was detected in young leaves and in tissue near the tuber skin but was highly expressed in flowers. The re sults indicate that PPO is present as a small multigene family in pota to and that each gene has a specific temporal and spatial pattern of e xpression.