Activities of the N-phenyl imide S-23142 in carotenoid-deficient seedlings of rice and cucumber

Abstract

The activity of S-23142 [ N-(4-chloro-2-fluoro-5-propargyloxyphenyl)-3,4,5,6-tetrahydrophthalimide], an experimental herbicide having diphenyl ether-type action, was examined in carotenoid-deficient materials. White seedlings of rice mutant which show tolerance to diphenyl ethers were completely killed by 0.1 μ M S-23142 and the tolerance to a diphenyl ether acifluorfen-ethyl (25 μ M) was lost under high light intensity (92 μE/m 2/sec). S-23142 was also active in cucumber seedlings with carotenoids depleted by fluridone grown under low intensity (0.14 μE/m 2/sec PAR) light that did not cause photobleaching of chlorophyll. The specific wavelength of light required for the action of S-23142 in yellow cucumber cotyledons treated with tentoxin, an inhibitor of chlorophyll formation, was 400 nm. As the effectiveness of the 400-nm light for inducing S-23142 action was not altered by the depletion of carotenoids by fluridone, the influence of carotenoids can be ruled out. The effectiveness of red light of 650 nm was greatly reduced in tissue grown under low light intensity or treated with tentoxin. These results indicate that S-23142 is active without the involvement of carotenoids and multiple photoreactions are involved in the herbicidal action of S-23142 in normal green tissue. The results also strongly suggest that chlorophyll or its related pigment(s) serves as one of the photoreceptors, although S-23142 is also active in achlorophyllous tissue.