Polyphenol Oxidase-Catalyzed Browning of Young Shoot Extracts of Citrus Taxa1

Based on the occurrence or absence of browning in young shoot extracts, Citrus taxa can be classified into 2 phenotypes: browning and nonbrowning. Browning results from the enzymatic oxidation of phenolic substrate present in the browning taxa. The enzyme responsible for browning is polyphenol oxidase ( ortho -diphenol oxidase, EC 1.10.3.1). Nonbrowning taxa lack the substrate(s) and have little or no polyphenol oxidase activity. Browning appears to be a dominant trait. It should be useful as a genetic marker and a taxonomic criterion.