Changes in the subcellular location of catalase and ℴ-diphenol oxidase during infection of potato tubers by Phytophthora erythrosepttica

Abstract

Differential centrifugation of homogenates of healthy potato tuber tissue cv. Majestic revealed that 24·2% of o -diphenol oxidase and 33·8% of catalase activities were sedimentable. Isopycnic density gradient ultra-centrifugation on sucrose gradients showed that most of the sedimentable activity of these enzymes in healthy tissues was associated with a particle having the characteristic peroxisome buoyant density ranging from 1·25 to 1·255. During early stages of infection there was a marked reduction in the amount of particulate catalase activity and an increase in the activity of this enzyme in the soluble phase of cell homogenates whereas the total catalase activity of tissue fell sharply. Infection was not accompanied by a reduction of the particle-bound component of o -diphenol oxidase activity, but the proportion of particulate activity fell since there was a pronounced increase in the amount of non-sedi-mentable activity. There was a considerable change during late stages of infection in the density of particles with which o -diphenol oxidase activity was associated. The particulate location of the mitochondrial marker enzyme, malate dehydrogenase, was abolished early in the infection process. These results are discussed in relation to known changes in the subcellular location of acid hydrolases during pink rot disease.