SYSTEMIC WOUND INDUCTION OF POTATO (SOLANUM-TUBEROSUM) POLYPHENOL OXIDASE

Plant polyphenol oxidases (PPOs) have long been reported to be inducib le upon biotic or abiotic wounding. However, observations of inducible PPO activity are frequently confounded by failure to distinguish PPO induction from loss of PPO latency, or by failure to distinguish PPO a ctivity from peroxidase activity. We report the systemic induction of PPO activity, and increased steady-state levels of PPOs and PPO mRNA i n potato (Solanum tuberosum L.) in response to wounding. During normal growth and development, PPO is present throughout potato leaf maturat ion, from the apical leaf node through node 11. In contrast, PPO mRNA is only detectable in apical leaf nodes 1-3. Wounding of potato leafle ts at nodes 6-8 results in 1.7-fold increase in PPO activity in apical leaf nodes 1-4 within 48 hr after wounding. The increases in PPO acti vity are accompanied by comparable increases in PPOs and PPO-specific mRNA. No PPO induction is observed in either leaf nodes 5 or 8. These results suggest that only those tissues which are developmentally comp etent to express PPO mRNA are capable of responding to the systemic wo unding signal by increased accumulation of PPO mRNA.