A full-length cDNA clone encoding apple (Malus domesticus) polyphenol
oxidase (PPO) was isolated from a fruit peel cDNA library. Southern an
alysis indicated that apple PPO is encoded by a divergent multigene fa
mily. BY northern analysis, PPO mRNA was only detected in a fruit samp
le taken one week after full bloom. PPO mRNA accumulated in wounded ti
ssues, and also in peel tissue showing the symptoms of superficial sca
ld, a post-harvest disorder. The induction of PPO mRNA provides the fi
rst evidence for transcriptional control of PPO expression after wound
ing or the manifestation of a physiological disorder.