Direct Assay of IAA Decarboxylation Rate in Excised Tobacco Pith: Relation to Aging

Abstract

Fresh and cultured tissues of Nicotiana tabacum Wis. Havana 38 were incubated with indole acetic-1-C14 acid (IAA* ) in wells suspended in scintillation counting vials; the evolved CO2 was trapped in potassium hydroxide at the bottom of the vial, and counted after addition of the scintillator fluid. The rate of decarboxylation per g dry wt. of tissue was higher in progressively lower (older) sections from a given stem. Tissues cultured on a medium containing IAA failed to develop the increased IAA* decarboxylating capacity found in tissues grown on basal medium, and remained like young tissue. Inactivity of young fresh pith was not due to lack of cofactors. These data conflict with the idea that IAA induces the enzyme system for its destruction, and support the concept that oxidative enzymes form in the absence of IAA.