IMPLICATIONS OF THE PHYLOGENETIC DISTRIBUTION OF POLYPHENOL OXIDASE IN PLANTS

A limited phylogenetic survey of the distribution of polyphenol oxidase (PPO: EC 1.10.3.2) was conducted in order to determine if this enigmatous enzyme is present in all plants groups or in only certain phylogenetic lines. Evidence for presence of the enzyme was gathered via enzyme assays using various recognized substrates and through the use a heterologous DNA sequence from the PPO of Vicia faba in DNA hybridization experiments and in polymerase chain reaction amplification of conserved sequence within the gene. Enzyme assays showed PPO activity in members of all eukaryotic groups tested, albeit at low levels in some groups, including green algae, mosses, and gymnosperms. DNA hybridization experiments showed varying degrees of signal strength obtained on the dot blots. This could mean limited homology between Vicia probe and target DNA or different copy number in the target DNA. Amplification experiments using primers for a 111 base pair region of the Vicia copper A binding region yielded 111 base pair products in all members of all phylogenetic groups tested. These data strongly suggest the presence of active PPO in all photosynthetic organisms more advanced than cyanophytes. This, along with data from studies with PPO-less mutants, implies some essential function of the enzyme in plants.