Indole‐3‐acetic Acid Levels and the Role of Indole‐3‐acetic Acid Oxidase in the Normal Root and Club‐root of Cabbage

Abstract

Abstract The auxin content of club‐root ( Plasmodiophora brassicae Wor.) is 50–100 times higher than that of normal cabbage root. The importance of this difference in the disease development is discussed. Both normal root and club‐root of cabbage contain allosteric IAA oxidase and IAA oxidase with ordinary kinetic properties. In normal cabbage root the allosteric one is associated with cell fractions sedimenting at 20,000 × g and 105,000 × g, in club‐root it remains in the supernatant after 105,000 × g centrifugation. IAA oxidase with conventional kinetic properties is present in both these tissues in the cell fraction sedimenting at 10,000 × g, which contains mainly cell wall fragments. It is concluded that IAA oxidase is not primarily involved in regulation of the endogenous IAA level.