Studies on the Physiological Changes in the Rice Plants Infected with Xanthomonas oryzae

II. Changes in the activities of peroxidase in the infected leaves

Abstract

The investigation was made to elucidate the differences in peroxidase activity between the compatible and incompatible infection of rice leaves with Xanthomonas oryzae. Peroxidase activity, which was measured by a colorimetric method, increased markedly as lesions enlarged in the susceptible leaves, and showed a value 1.6 to 1.8 times higher as compared with that of leaves at an onset of inoculation. In the resistant leaves, on the contrary, the activity increased slightly, and showed a value 1.2 to 1.4 times of initial activity. On the other hand, in the healthy or needle pricked uninoculated leaves very slight increases (1.1 times) occurred within 14 days after the onset of experiment. The activity in the lower aged healthy leaves was higher than that in the upper immature ones. Both the decrease in chlorophyll content and the increase, in peroxidase activity were greater in the susceptible leaves than in the resistant or the healthy ones, then negative correlation between the chlorophyll content and the peroxidase activity was obviously observed. Eight bands of peroxidase isozymes, which were revealed by a polyacrylamide gel disc electrophoresis, were detected from both gels of infected and healthy leaves, but the intensity of staining by benzidine hydrochloride-H₂O₂ was highest in the susceptible leaves, the resistant leaves followed, and the healthy leaves was lowest. These differences in the intensity of staining were marked especially in the three bands among eight ones. These three isozymes were stained much densely in the lower leaves than in the upper leaves. From the above results, it was evident that the peroxidase activity might be increased in the infected susceptible leaves and might not be involved in resistance expression, and that the activity might be increased in the susceptible leaves in accordence with accerelation of senescence in the infected tissues, since qualitative difference was not observed between the healthy and infected leaves.