The Effect of Pseudomonas putida Colonization on Root Surface Peroxidase

Abstract

Increased activities of peroxidase and indole 3-acetic acid (IAA) oxi-dase were detected on root surfaces of bean (Phawolus vulgaris) seedlings colonized with a soil saprophytic bacterium, Pseudomonas putida. IAA oxidase activity increased over 250-fold and peroxidase 8-fold. Enhance-ment was greater for 6-day-old than for 4-or 8-day-old inoculated plants No IAA oxidase or peroxidase activities were associated with the bacte-rial cells. Native polyacrylamide gel electrophoresis demonstrated that washes of P. putida-inoculated roots contained two zones of peroxidase activity. Only the more anodic bands were detected in washes from noninoculated roots. Ion exchange and molecular sizing gel chromatog-raphy of washes from P. putida-colonized roots separated two fractions of peroxidase activity. One fraction corresponded to the anodic bands detected in washes of P. putida inoculated and in noninoculated roots. A second fraction corresponded to the less anodic zone of peroxidase, which was characteristic of P. putida-inoculated plants. This peroxidase had a higher IAA oxidase to peroxidase ratio than the more anodic, common enzyme. The changes in root surface peroxidases caused by colonization by a saprophytic bacterium are discussed with reference to plant-patho-gen interactions.