Abstract
This paper deals with the changes in the respiration of leaf tissues infected by Piricularia oryzae. Rice varieties, Aiti-asahi (susceptible) and Kanto 53 (resistant) were used. Leaf lesions occurring on these varieties were classified into 5 types as shown diagramatically in Fig. 1. Lesions of the types 3, 4 and 5 were used for the experiments. Types 4 and represent the lesions on the susceptible var5ety and type 3 represents the lesion on the resistant variety. From each lesion, the central necrotic area is removed and a marginal zone of about 3mm width was taken as the material for measurement of the respiration rate. If the tissue is resistant, the respiration is stimulated to some extent, not exeeding over two times as that of non-infected tissue, while f the tissue is susceptible, the respiration is stimulated up to 4 to 5 times. The RQ gives usually 0.8 in the healthy, and 0.9 in the infected tissues. The diminution of Pasteur effect (shown by QairCo2/QN2Co2) is remarkeble in the susceptible tissue, but in the resistant tissue it is not affected. The respiration of resistant tissue is inhibited by 10-25 per cent by such metal enzyme inhibitors as NaN3, 8-hydroxyquinoline, and salicylaldoxime, while, that of susceptible tissue is not affected, suggesting that flavoprotein enzyme works as terminal oxidase in the infected tissue, in place of metal protein enzymes. The above mentioned change of terminal oxidase system in the infected tissue is probable because it is already known that P. oryzae produces two toxins, α-picolinic acid. and piricularin and that these are inhibitory to metal enzymes (Tamari et al.). The writers consider that the main cause of unusual stimulation of respiration and the diminution of Pasteur effect in susceptible tissue is the change of terminal oxidase, from metal protein to flavoprotein.
