Respiration and terminal oxidases in tomato leaves infected by Phytophthora in festans

Abstract

The respiratory rate of tomato leaf tissue inoculated with race 1 (compatible) of Phytophthora infestans increased to 46% greater than that of control tissue at 72 b but dropped to a 21% increase at 96 h after inoculation. The respiratory rate of tomato tissue inoculated with race 0 (incompatible) was 13 to 22% greater than that of control tissue over a 48 to 96 h time period. In vitro activities of terminal oxidases in the compatible reaction were assayed spectrophotometrically. Ascorbic acid oxidase activity showed a 75% increase in the infected tissue at both 72 and 96 h. Polyphenoloxidase activity was increased 75% at 72 h and fivefold at 96 h in the infected tissue. Peroxidase activity was increased threefold at 72 h and sixfold at 96 h in infected tissue. No difference in catalase and cytochrome oxidase activity could be measured between control and infected tissue. Activity of glycolic acid oxidase was 40% lower at 72 h and 25% lower at 96 h in infected tissue than in control tissue. Control and infected tissue showed little difference in the in vivo activity of copper oxidases. Respiration rates and the activities of terminal oxidases were measured in mycelial extracts of tomato races 0 and one of P. infestans.