Abstract
The fungicidal activity of phenylmercuric acetate (PMA) was assayed on the conidia of Cochliobolus miyabeanus by the use of slide-germination test method. The ED 50 of PMA was 0.04ppm, when PMA alone was dissolved in water. But the addition of 1ml of rice leaf juice per 2.5ml of the test solution raised the ED 50 of PMA up to about 20ppm. The juice was thus prepared by grinding 10g of leaves with water at 5°C, filling up to 150ml and filtrating.
The rate of the detoxication of PMA by the juice increased parallel to the amount of the added juice. The effect of the juice decreased by the oxidation during extraction and storage at 5°C. The dialysis of the juice revealed that the effective substance was present mainly in the protein fraction and partly in the low molecular fraction. PMA was detoxified by the addition of thiol compounds, such as cysteine, glutathione (reduced), egg-albumin, yeast-extract and sodium thiosulfate, as well as the rice leaf juice. Amino acids, vitamins, carbohydrates and inorganic salts, all of which did not contain the thiol-group, did not detoxify PMA.
From these results, the author concluded that the detoxication of PMA by the rice leaf juice was due to the formation of the mercaptide of phenylmercuric group with the thiol-group mainly of protein and partly of low molecular substances such as glutathione (reduced) present in the juice.
