Abstract
Effects of sunlight and soil microorganisms on the decomposition of optical isomers of naproanilide were investigated in relation to the plant growth-regulating activities. The results obtained are as follows:
1) Raphanus test, tomato-leaf epinasty test and root growth test were performed for the determination of the auxin activity. In all the tests, the activity was found to be high in the (+)-isomer and racemiç modification of naproanilide, but low in the (-)-isomer. In these tests, the auxin activity of the (+)-isomer of naproanilide was approximately 2.1 times as high as that of the racemic modification. In contrast, the auxin activity of the isomer of NOP, a decomposed product of naproanilide, was similar to that of each of the corresponding isomers of naproanilide, but the auxin activity of the (+)-isomer and racemic modification was higher than that of naproanilide (Fig. 1, 2 and 3), respectively.
2) In the herbicidal activity on various paddy weed, the (-)-isomer of naproanilide showed a herbicidal activity even at a dose of 20g (a.i./a). However the (+)-isomer showed a high herbicidal activity, which the racemic modification showed a moderate activity (Table 1).
3) Optical isomers and racemic modificatson of naproanilide were decomposed rapidly by exposure to sunlight with a half life of 11.2min for the (+)-isomer, 11.2min for the (-)-isomer and 10.8min for the racemic modification, showing no significant differences in the photolysis of these compounds (Table 2).
4) The racemic modification of naproanilide in soil-water under sterile conditions was hardly decomposed. which the (+)-isomer and racemic modification of naproanilide in soil-water under non terile conditions were arpidly decomposed after an interval of period about 48hr, and about 72hr in the case of the (-)-isomer. Thus there was a clear difference in the rate of microbial decomposition of the optical isomers in the soil suspension (Fig. 4).
