The Apparent Involvement of Polyphenol Oxidase and Phloridzin in the Production of Apple Rooting Cofactors

SummaryPolyphenol oxidase (PPO) activity and phloridzin content in vacuum-extracted xylem sap of M.26 apple cuttings increased between mid-December and late January, preceding an increase in endogenous rooting cofactor activity and the rooting of cuttings between late January and mid-February 1979. When tested by the mung bean bioassay in the presence of indolylbutyric acid (IBA) many phenolic substances improved rooting, especially oxidized forms and derivatives. The product of a reaction between polyphenol oxidase (PPO) and phloridzin in vitro was markedly active in the mung bean test and showed certain similarities with the extracted endogenous cofactor following chromatography. The cofactor activity of sap extracted during the period of poor rooting in midwinter was increased by adding both PPO and phloridzin and the rooting of IBA-treated cuttings was increased by pre-treatment with the products of a PPO and phloridzin reaction.