The Effect of Phenazine-5N-monooxide upon the Respiration and Photosynthetic Oxygen Evolution of Rice Plant Leaf and Photodegradation on the Leaf

Abstract

1. The effect of phenazine-5N-monooxide, effective disinfectant against leaf blight disease of rice plant, upon the respiration and photosynthetic oxygen evolution of the rice leaf and photodegradation of the compound were investigated.
2. Phenazine-5N-monooxide did not give any influence upon the respiration and photosynthetic oxygen evolution of the detached whole leaves at the concentration of 2.5μg/ml, which is more than a half inhibitory concentration for the causal bacterium.
3. Phenazine-5N-monooxide also did not give any influence upon either the respiration or photosynthetic oxygen evolution of the detached whole leaves when aqueous suspension at 200ppm was sprayed to the potted plant, this amount being entirely enough to control the disease.
4. In the experimental run using slices of the plant leaves, the photosynthetic oxygen evolution was suppressed by the addition of phenazine, whereas phenazine-5N-monooxide did not give any marked inhibitory effect indicating that the introduction of N-oxide group masked the undesirable properties of the mother compound. The reductive cleavage of the N-oxide bond of phenazine-5N-monooxide by the thin slices of rice plant leaves or leaves homogenate was not observed.
5. Phenazine-5N-monooxide in the solution was gradually changed to unidentified photodegradated compounds having lower bioligical activity by a non-biological photochemical reaction.
6. Unidentified photodegradated compound UP-1 isolated in crystals had m.p. 131°C empirical formula C₁₂H₈N₂O, and M.W. 197. It seemed an isomeric compound of phenazine-5N-monooxide.