Catechol Oxidase in Suspension Cultures of Apple Fruit—The Effects of Growth Regulators

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Abstract
Growth and catechol oxidase activity were followed in suspension cultures of cells derived from apple fruit. In cultures which required the addition of hormones, enzyme activity was affected by 2, 4-D (2, 4-dichlorophenoxyacetic acid) and kinetin via their effect on growth. Exogenous hormones did not affect catechol oxidase activity of habituated cultures. Ethylene and PCIB (α-4-chlorophenoxyisobutyric acid) rapidly depressed enzyme activity in all cell fractions, but only at concentrations which repressed growth. Ethionine caused an immediate decrease in enzyme activity which preceded the repression of growth. Ethionine did not inhibit enzyme activity in vitro. Possible mechanisms of the action of ethionine are discussed and the formation of a specific inhibitor is hypothesized.