Hiromichi Oshio

In vitro mode of action of N-Phenylimide photobleaching herbicides

Abstract The effect of N-Phenylimide photobleaching herbicides on in vitro synthesis of protoporphyrin was examined. The N-phenylimide photobleaching herbicide S-23142 [N-(4-chloro-2-fluoro-5-propargyloxyphenyl)-3,4,5,6-tetrahydrophthalimide] inhibited the Mg-protoporphyrin IX synthesis of intact plastids by 50% at 10−10 M. Protoporphyrin IX synthesizing activity was solubilized from plastid membranes by n-dodecyl β- d -maltoside, and the solubilized activity was inhibited by several photobleaching herbicides. In vitro binding of N-phenylimide photobleaching herbicide, S-23121 [N-[4-chloro-2-fluoro-5-[(1-methyl-2-propynyl)oxyl]phenyl]-3,4,5,6-tetrahydrophthalimide], to a solubilized plastid fraction was examined. A good correlation between protoporphyrin IX synthesizing activity and [14C]S-23121 specific binding was observed. Binding site affinity (Kd) was 8.9 – 9.8 nM. The binding was displaced by a diphenylether photobleaching herbicide, acifluorfenethyl, and another N-phenylimide, S-23142, but not by a photosystem II electron transport inhibitor, DCMU. Bound [14C]S-23121 was dissociated by an excess of cold S-23121, which indicated the reversible binding of S-23121.

Diphenylether-like physiological and biochemical actions of S-23142, a novel N-phenyl imide herbicide

Abstract Several physiological and biochemical actions of a new experimental herbicide, S-23142 [N-(4-chloro-2-fluoro-5-propargyloxyphenyl)-3,4,5,6-tetrahydrophthalimide], have been investigated. S-23142 was active under the presence of light and oxygen. Photosynthetic CO2 fixation in soybean began to decrease 4–5 hr after the foliar treatment of S-23142, being accompanied by the appearance of visible bleaching and wilting of the plants. A large amount of ethane, the products of peroxidation of unsaturated fatty acids, was produced from the cotyledon discs of cucumber (Cucumis sativus L.) treated with S-23142. Leakage of ATP was also observed. S-23142 did not inhibit photosynthetic oxygen evolution of the discs just after the application; however, the oxygen evolution rate decreased as the treated discs produced ethane. The results suggest that cell membrane and chloroplast membrane were deteriorated by the membrane lipid peroxidation. S-23142 also induced ethylene production and a high level of phenylalanine-ammonia lyase activity in cucumber cotyledon, which was regarded as the phenomena of stress response. Only the ethylene production was inhibited by aminoethoxyvinylglycine and cycloheximide, while the ethane production was not affected. All of these actions of S-23142 were essentially the same as those of acifluorfen ethyl except that the activity of S-23142 was more than 10 times higher than that of acifluorfen ethyl. These data strongly suggest that S-23142 belongs to the same group as diphenylethers in its mechanisms of action despite the difference in chemical structure.

Isolation and Characterization of a Chlamydomonas reinhardtii Mutant Resistant to Photobleaching Herbicides

A group of highly active N -phenylimide photobleaching herbicides have been synthesized. These N -phenylimide herbicides as well as diphenyl ether herbicides induce protoporphyrin IX accumulation and inhibit protoporphyrinogen oxidase activity at extremely low concentrations in higher plants. The binding of a 14C -labeled N -phenylimide herbicide S-23121 [N-[4-chloro- 2-fluoro-5-[(1-m ethyl-2-propynyl)oxy]phenyl]-3,4,5,6-tetrahydrophthalimide] to the solubilized plastid fractions of greening corn seedlings is competed by the diphenyl ether herbicide acifluorfen-ethyl, but not by diuron, an inhibitor of photosynthetic electron transport. These results indicate a similar mode of action for both N -phenylimide and diphenyl ether herbicides. In order to investigate the mechanism of photobleaching herbicides at the molecular level, a strain of Chlamydomonas reinhardtii RS-3 resistant to N -phenylimide S-23142 [N -(4-chloro- 2-fluoro-5-propargyloxyphenyl)-3,4,5,6-tetrahydrophthalimide] was isolated by mutagenesis with N -m ethyl-N′-nitro-N -nitrosoguanidine. The 90% inhibition concentration of N -phenylimide S-23142 for growth of RS-3 was 100 times higher than that for wild type. Maximum accumulation of protoporphyrin IX was reached at 0.03 μᴍ of S-23142 for the wild type and 3 μᴍ for RS-3. RS-3 was resistant to oxadiazon, oxyfluorfen and acifluorfen-ethyl which had been shown to have the same mechanism of action as N -phenylimide herbicides, but not to paraquat, diuron or fluridone. Genetic analysis of RS-3 strain showed that the resistance results from a dominant mutation ( rs-3) in the nuclear genome. The magnesium protoporphyrin IX synthesizing activity from 5-am inolevulinic acid in chloroplast fragments isolated from RS-3 was less sensitive to S-23142 than that from wild type (CC-407). Protoporphyrinogen oxidase activity in Percoll™ -purified chloroplasts from RS-3 was also less sensitive to S-23142 than that from wild type. These results indicate that the resistance of RS-3 is specific for photobleaching herbicides, and that the mutation is related to protoporphyrinogen oxidase, the primary site of the photobleaching herbicide action.

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 μM S-23142 and the tolerance to a diphenyl ether acifluorfen-ethyl (25 μM) was lost under high light intensity (92 μE/m2/sec). S-23142 was also active in cucumber seedlings with carotenoids depleted by fluridone grown under low intensity (0.14 μE/m2/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.

S-23031, a New Post-Emergence Herbicide for Soybeans

S-23031, pentyl 2-chloro-4-fluoro-5-[(3,4,5,6-tetrahydro)phthalimido]phenoxyacetate, is a new post-emergence herbicide for broad-leaved weed control in soybeans. S-23031 is a fast acting herbicide and effective against various kinds of broad-leaved weeds with good crop safety at 8 – 125 g a.i./ ha in post-emergence treatment. Weed control spectrum of S-23031 includes troublesome weeds such as velvetleaf, prickly sida, jimsonweed and common lambsquarters. S-23031 shows excellent tank-mix compatibility with other soybean herbicides such as imazethapyr, bentazone and clethodim.