Increase of polyphenoloxidase activity by a local virus infection in uninoculated parts of leaves

Abstract

A spectrophotometric method, using chlorogenic acid as a substrate, for determining polyphenoloxidase activity of tobacco leaves is described. This method was used to measure polyphenoloxidase in tobacco mosaic virus-inoculated leaves of Nicotiana tabacum var. Samsun NN, a local-lesion host for this virus. An increase in polyphenoloxidase activity was found with a maximum about 4 days after inoculation. The Michaelis constant, K m , was the same for enzyme from healthy and infected tissue, an indication that the differences were only quantitative, not qualitative. The increase of polyphenoloxidase was not restricted to the inoculated parts of the leaves where virus multiplication occurs and local lesions develop, but was also found in the uninoculated parts. This induction occurred within 7 hours after inoculation of the leaves.