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

V. Permeability Changes in Infected Rice Plants

Abstract

Permeability changes in rice leaves inoculated with Xanthomonas campestris pv. oryzae were investigated by measuring the leakage of electrolytes and ¹⁴C-assimilates to gain an understanding of the mechanisms of pathogenesis. In experiments with detached rice leaves, pieces 6mm in length were incubated in the bacterial suspension (about 10⁸cells/ml) for 72hr at 25 C in a shaking condition. The bacterial suspension was then replaced by distilled water, continuously shaken for an additional 4hr at 25 C, and the conductivity of this bathing solution was measured. The electrolyte leakage was 2 to 3.5times higher in inoculated susceptible leaf pieces than in the non-inoculated control, but was only 1.4times higher in resistant leaves. No similar increment of electrolyte leakage was observed with heat-killed bacteria, centrifuged supernatants of culture suspension or bacterial suspension to which chloramphenicol had been added. From these results, it is clearly evident that living bacteria can induce permeability enhancement of rice leaf pieces. In experiments with attached rice leaves, periodic measurement of the leakage of electrolytes and ¹⁴C-assimilates revealed a significant increase in susceptible leaves from just prior to symptom development, and a slight increase from the same time in resistant leaves.