Ref ID : 4558
Hiromichi Oshio, Hideyuki Shibata, Nobuaki Mito, Masako Yamamoto, Elizabeth H. Harris, Nicholas W. Gillham, John E. Boynton, and Ryo Sato; Isolation and Characterization of a Chlamydomonas reinhardtii Mutant resistant to Photobleaching Herbicides. Z.Naturforsch. 48c:339-344, 1993
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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-methyl-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 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-methyl-N'-nitro-N-nitrosoguanidine. The 90% inhibition concentration of N-phenyl-imide 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 µM of S-23142 for the wild type and 3 µM for RS-3. RS-3 was resistant to oxadiazon, oxyfluorfen and acilfuorfen-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-aminolevulinic 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(TM)-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.