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

Plant polyphenol oxidases (PPOs) have long been reported to be inducible 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 activity from peroxidase activity. We report the systemic induction of PPO activity, and increased steady-state levels of PPOs and PPO mRNA in potato (Solanum tuberosum L.) in response to wounding. During normal growth and development, PPO is present throughout potato leaf maturation, from the apical leaf node through node 11. In contrast, PPO mRNA is only detectable in apical leaf nodes 1-3. Wounding of potato leaflets 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 activity 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 competent to express PPO mRNA are capable of responding to the systemic wounding signal by increased accumulation of PPO mRNA.