Plant growth-regulating activity, and photolytic and microbial decomposition of optical isomers of naproanilide

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).