Polyphenol oxidase is induced by chilling and wounding in pineapple

Polyphenol oxidase (PPO) activity was found to be low in the leaves, roots, inflorescence tissues and developing and mature fruit of pineapple (Ananas comosus L.). In fruit affected by the chill-induced internal browning diso rder known as Blackheart, PPO activity was 10-fold higher than in unaffecte d fruit, and there was a direct correlation between PPO activity and the se verity of Blackheart symptoms. Degenerate oligonucleotide primers were desi gned to conserved regions of plant PPO genes, and used to amplify two disti nct pineapple PPO cDNAs, designated PINPPO1 (2181 bp) and PINPPO2 (1319 bp) , which share 81% sequence identity at the DNA level and show a high degree of homology to other plant PPO genes. PINPPO1 encodes a peptide of 604 ami no acids, including a putative transit peptide of 95 amino acids and two co pper-binding regions, CuA and CuB, which are highly conserved in plant PPOs . Southern analysis suggested the presence of at least four PPO genes in pi neapple. Expression of PINPPO1 and PINPPO2 was low in roots, leaves, inflor escence tissues and developing fruit, but was strongly up-regulated in resp onse to chilling and wounding. These results indicate that PPO is synthesis ed de novo in response to chilling of pineapple fruit, and implicate a role for the enzyme in the development of Blackheart disorder.