Peroxidizing Phytotoxic Activity of Pyrazoles

Abstract

Using autotrophic Scenedesmus cells and maize protoporphyrinogen-IX oxidase, twelve pyrazole compounds recently synthesized were assayed with respect to peroxidizing phytotoxic activity. Three pyrazoles, namely 1-(4-chloro-2-fluoro-5-propargyloxyphenyl)-3, 5-dimethyl-4-nitropyrazole, 5-amino-4-cyano-l-(2, 6-dichloro-4-trifluoromethylphenyl)pyrazole and 5chloro-l-(4-chloro-5-difluoromethoxy-2-fluorophenyl)-3, 4-tetramethylenepyrazole, strongly inhibited growth of the Scenedesmus cells and caused severe chlorophyll deficiency (bleaching activity) at a 10-6 M concentration. The three pyrazoles mentioned were selected for a further quantitative study to determine whether the chlorophyll decrease observed was due to inhibition of pigment biosynthesis or to peroxidative destruction of existing chlorophyll. The pyrazoles inhibited protoporphyrinogen-IX oxidase, caused not only accumulation of protoporphyrin-IX but also light-induced ethane formation. Thus, the three pyrazoles (1, 11 and 12) were identified as peroxidizing herbicides. A 1-(4-chloro-2-fluoro-5-substituted)phenyl moiety at the pyrazole ring appears to be essential for producing active peroxidizing compounds.

Protoporphyrinogen-IX Oxidase Inhibition of New Diphenyl Ethers

“…After incubation, cell growth, chlorophyll content and ethane formation were determined according to our methods. 4,6,11,12) Cell growth was expressed as pcv/ml of the algae culture volume. Total chlorophyll content was determined spectroscopically in a methanolic extract.…”

“…[3][4][5][6] Recently, the protoporphyrinogen-IX oxidase (Protox) inhibition by these compounds has been included in the peroxidation assay. 7 In this paper, the peroxidizing activity of new diphenyl-ether type herbicides was investigated using Scenedesmus cells and cell-free Protox activity of maize.…”