Rhodanine (2-thioxo-4-thiazolidinone) and 2(5H)-thiophenone inhibit germination and root growth of several plants. Using Scenedesmus acutus and Marchantia polymorpha L., these compounds were assayed with respect to degradation of chlorophyll, light-induced ethane formation and growth inhibition to determine the action mechanism. Chlorophyll reduction and growth inhibition of liverwort cells were quantitatively correlated with light-induced ethane formation of Scenedesmus in the presence of these compounds. Furthermore, we found that rhodanine itself decreased the chlorophyll content in liverwort cells and produced ethane with Scenedesmus cells in the light although no protoporphyrin IX (PPIX) accumulated. Diuron did not influence ethane formation with these two compounds as is observed with peroxidizing herbicides like oxyfluorfen. Apparently, rhodanine prevents PPIX accumulation by AFM.

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Safening effects of 1, 8-naphthalic anhydride (NA) on corn (Zea mays L.) plants treated with bensulfuron-methyl [BEN; methyl-2-[[[[{(4, 6-dimethoxy-2-pyrimidinyl)amino}carbonyl]amino]sulfonyl]methyl]benzoic acid] or imazaquin [IMA; 2-{4, 5-dihydro-4-methyl-4-(1-methyl ethyl)-5-oxo-1H-imidazol-2-yl}-3-quinolinecarboxylic acid] were investigated. NA safened the plants treated with BEN or IMA with a safening index of 10.2 or 5.1, respectively. Optimum application of NA was achieved by seed dressing at 0.2% (w/w) by seed weight. The safening effect of NA tended to be increased with an earlier application of the herbicides. NA stimulated the activities of acetolactate synthase (ALS) and acetyl CoA carboxylase (ACCase) by 32 and 216%, respectively. The herbicides had no inhibitory effect on ACCase activity either from control or from NA-treated plants. However, the herbicides greatly inhibited ALS activity. The herbicidal inhibition of ALS was alleviated by NA treatment. The herbicides induced the accumulation of pyruvate in treated tissues, but no pyruvate accumulation occurred in NA-treated plants. Therefore, it can be concluded that NA protects plants from the herbicide injury at least partly through the enhancement of ALS and ACCase activities, and the reduction of pyruvate accumulation.

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Thirty-seven strains of bacteria belonging to various taxonomic positions were examined for the degrading ability of a fungicide chlorothalonil, 2, 4, 5, 6-tetrachloroisophthalonitrile, in nutrient broth. All of the bacteria degraded chlorothalonil, except Pimelobacter sp. A3. On the chlorothalonil-suspended agar, most of the Gram-negative bacteria grew but many Gram-positive bacteria did not grow. No production of ¹⁴CO₂ was observed in the degradation of [1-nitrile-¹⁴C]-chlorothalonil. The degradation of chlorothalonil was mainly observed in the exponential growth stage of bacteria. Methylthiotrichloroisophthalonitrile and hydroxytrichloroisophthalonitrile were major metabolites. Trichloroisophthalonitrile was detected as a minor metabolite. These findings suggested that the capability to degrade chlorothalonil by the substitution reaction of chlorine atoms on aromatic ring with methylthio group, hydroxyl group or hydrogen is ubiquitous in bacteria.

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A rapid multiresidue method of pesticides using macroporous diatomaceous earth (MDE) column and silica gel cartridge for cleanup procedure was developed. The method was based on the experimental elution profiles of 174 compounds. The majority of pesticides were eluted with hexane and 15% acetone in hexane from the MDE column and the silica gel cartridge, respectively. Recoveries of a large number of pesticides from each column were satisfactory except for a few easy hydrolyzed compounds or high polar compounds. Synthetic pyrethroids were eluted into several fractions from the MDE column. The availability of the method was evaluated on recoveries from tomato fortified with 49 compounds. Mean recoveries were ranged from 48% for acephate to 133% for fenitrothion and limits of detection (LOD) were between 0.003 and 0.01ppm.

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The effects of trichloromethyl-1, 3, 5-triazines on the ammonia oxidizing activity of the nitrifying bacteria Nitrosomonas europaea ATCC 25978 and Nitrosomonas sp. TK 794 were investigated. Trichloromethyl-1, 3, 5-triazines inhibited nitrite production in the ammonia oxidation step, but showed no inhibition to the hydroxylamine oxidation step of both ATCC 25978 and TK 794. The ammonium oxidation by ATCC 25978 was affected more strongly than that by TK 794. These results suggest that the trichloromethyl-1, 3, 5-triazines may inhibit the ammonia monooxygenase of Nitrosomonas spp. Quantitative structure activity relations (QSAR) studies were carried out between the nitrification inhibitory activity (pI₅₀) values on both strains and a hydrophobic parameter (log octanol-water partition coefficient, logP) by means of regression analysis. The optimum logP of trichloromethyl-1, 3, 5-triazines for both ATCC 25978 and TK 794 was calculated as about 4.

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A herbicidal peroxidizer, N-(4-bromophenyl)-3, 4, 5, 6-tetrahydroisophthalimide was isomerized to N-(4-bromophenyl)-3, 4, 5, 6-tetrahydrophthalimide directly and rapidly in the presence of equine glutathione S-transferase (GST) with reduced glutathione (GSH), and was also converted into the imide via 4-bromophenyl-3, 4, 5, 6-tetrahydrophthalamic acid by hydrolysis. GST converts 5-(4-bromophenylimino)-3, 4-tetramethylene-1, 3, 4-thiadiazolidin-2-one into its isomer, 4-bromophenyl-1, 2-tetramethylene-1, 2, 4-triazolidin-3-one-5-thione, but hardly converts 5-(4-bromophenylimino)-3, 4-tetramethylene-1, 3, 4-thiadiazolidine-2-thione into 4-bromophenyl-1, 2-tetramethylene-1, 2, 4-triazolidine-3, 5-dithione. N-(4-Bromophenyl)-3, 4, 5, 6-tetrahydroisophthalimide and 5-(4-bromophenylimino)-3, 4-tetramethylene-1, 3, 4-thiadiazolidin-2-one strongly inhibit protoporphyrinogen oxidase activity after isomerization to their isomers. This finding, together with our previous results, reveals that GST catalyzes a quick activation of N-aryl-3, 4, 5, 6-tetrahydroisophthalimides and 5-arylimino-3, 4-tetramethylene-1, 3, 4-thiadiazolidin-2-ones in the presence of GSH by isomerization. Although GST has generally been described as a detoxifying enzyme in pesticide toxicology, the herbicide activation by the metabolic isomerization shown in this study is a new function of GST and GSH.

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[in Japanese]

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[in Japanese]

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