Abstract
The relationship between the increase of bacteria and the changes in respiratory rate of rice leaves infected by Xanthomonas oryzae was examined.
In the susceptible leaves, the bacteria multiplied rapidly, and reached to 106∼107 cells, when lesion appeared 7 to 14 days after inoculation. Oxygen uptake increased markedly after the first appearance of the symptom, and showed a value 1.7 times as high compared with that of healthy tissues. A high correlation between the number of bacteria and the degree of oxygen uptake was found.
While, in the resistant tissues, the bacteria multiplied gradually to 105∼106 cells, then stopped their increasing, without any visible lesion. A rapid increase in oxygen uptake during the earlier phases of infection was not observed, and the increase at the later phases was limited only 1.3 times compared with that of healthy tissues. On the other hand, in the rice leaves inoculated with the incompatible bacterium X. phaseoli, neither the disease occurrence nor the increase in oxygen uptake was observed.
The investigation with leaf pieces variously distant from inoculated point proved that both the number of bacteria and the rate of respiratory enhancement decreased proportionally with the distance.
It was presumed that the enhanced uptake of oxygen was essentially a host response to the pathogen rather than a reflection of pathogen respiration.
