The effects of some commercial herbicides and N-heterocyclic compounds structurally related to corn root constituents on N₂O-emitting soil bacteria were examined. In the N₂O emission assay, two N₂O-emitting eubacteria, the incomplete denitrifier Pseudomonas sp. 10CFM5-1B and Pseudomonas sp. 10CFM5-2D (both isolated from Andisol corn farmland in Hokkaido), were used. We found that methyl viologen dichloride (Paraquat®) at 2 µM significantly repressed N₂O emission by the active denitrifying bacteria. A corn antifungal secondary metabolite, 6-methoxy-2-benzoxazolone (MBOA), also repressed pseudomonad denitrifiers at a concentration of 10 µM. Other herbicides such as simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) and amitrole (3-amino-1,2,4-triazole) accelerated N₂O emission by Pseudomonas sp. 10CFM5-1B at 2 or 10 µM. It was thus shown that methyl viologen dichloride may have somewhat contributed to the repression of global warming by suppressing N₂O production in farmland soils. Some herbicides, including amitrole and other triazole-type chemicals, may instead have the potential to activate soil N₂O emission.

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Cucumber (Cucumis sativus) plants were found to exude at least 12 germination stimulants for root parasitic weeds including 5 known strigolactones, 7-oxoorobanchol, 7-oxoorobanchyl acetate, orobanchol, orobanchyl acetate, and 4-deoxyorobanchol. Two novel germination stimulants were purified from cucumber root exudates and their structures were determined to be 7α- and 7β-hydroxyorobanchyl acetate by 1D and 2D NMR spectroscopy, and ESI- and EI-MS spectrometry. The stereochemistry was determined by NOE measurement and by comparing the CD spectra with those of the synthetic standards of four stereoisomers of orobanchol. 7α- and 7β-Hydroxyorobanchol were detected by LC-MS/MS, and GC-MS analysis of purified sample confirmed their structures. The germination stimulation activities of 7α- and 7β-hydroxyorobanchyl acetate on Orobanche minor were comparable to those of orobanchyl acetate and 7-oxoorobanchyl acetate. By contrast, 7β-hydroxyorobanchyl acetate was a highly potent germination stimulant for Phelipanche ramosa inducing more than 50% germination at 10 pM.

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Many entomopathogenic fungi have been demonstrated to be potential agents for efficiently controlling mosquito populations. In the present study, we investigated a bioreactor system to produce metabolites and conidia by combining technological advantages of submerged and solid-state fermentations. The efficiency of fungal products was tested toward mosquitoes. Aspergillus clavatus (Eurotiales: Trichocomaceae) was grown by semi-solid-state fermentation in a bioreactor for up to 7 days. Depending on conidial doses (2.5×10⁷, 5×10⁷, 7.5×10⁷, 10×10⁷ and 12.5×10⁷ conidia/mL), mortality ranged from 37.2±15.0 to 86.3±5.0% toward larvae and from 35.8±2.0 to 85.2±1.5% toward adults. The metabolites (10, 20, 40, 60, 80 and 100% v/v) yielded mortality from 23.7±15.0 to 100.0±0.1% toward larvae, and two sprayed volumes (5 and 10 mL) reached 45.5±1.4 and 75.6±2.6% mortality, respectively, toward adults.

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Insect GABA receptors (GABARs) represent important targets for insecticides. Thirteen iminopyridazine GABA analogs were synthesized and evaluated for their antagonism of three cloned insect GABARs. Of the synthesized analogs, 4-[4-cyclobutyl-1,6-dihydro-6-imino-3-(2-naphthyl)pyridazin-1-yl]butyronitrile greatly reduced GABA-activated responses in small brown planthopper (SBP) and common cutworm (CC) GABARs at 100 µM. Removal of the cyclobutyl group did not affect the levels of inhibition in both GABARs, whereas it increased the inhibition levels in housefly (HF) GABARs to afford an analog with an IC₅₀ of 75.5 µM. 4-[3-(4-Biphenylyl)-1,6-dihydro-6-iminopyridazin-1-yl]butyronitrile and the 3-(2-fluoro-4-biphenylyl) congener exhibited >80% inhibition in SBP and CC GABARs at 100 µM. These analogs showed relatively potent antagonism of HF GABARs, with IC₅₀s of 37.9 µM and 42.3 µM, respectively. Ethyl 3-[3-(4-biphenylyl)-1,6-dihydro-6-iminopyridazin-1-yl]propylphosphonate was the most potent inhibitor of GABA-induced currents in HF GABARs, with an IC₅₀ of 18.8 µM. These findings suggest that the iminopyridazine analogs could be leads for the development of insecticides.

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Novel meta-diamide insecticides [3-benzamido-N-(4-(perfluoropropan-2-yl)phenyl)benzamides] are a distinct class of insect RDL GABA receptor antagonists that have been suggested to act at or near G336 in the M3 region of the Drosophila RDL GABA receptor. Here, we demonstrate the low-level antagonist activities of novel meta-diamides against the human GABA type A receptor (GABA_AR) α1β2γ2S, mammalian GABA_AR α1β3γ2S, and the human glycine receptor (GlyR) α1β. The Gly residue at position 336 in the M3 region of the Drosophila RDL GABA receptor is essential for its high sensitivity to meta-diamides. Therefore, the effects of an equivalent mutation (A288G) in human GlyR α1 on the antagonist activities of meta-diamides were studied. The A288G mutation dramatically increased the antagonist activities of meta-diamides against GlyR α1. Thus, A288 in GlyR α1 is important for this receptor’s sensitivity to meta-diamide insecticides. Our study is useful for understanding the mechanisms underlying meta-diamide selectivity.

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The target site of tolprocarb, a novel systemic fungicide used for controlling rice blast, was investigated. Tolprocarb decolorized the mycelia of Magnaporthe grisea; the decolorization was reversed by adding scytalone or 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN). This result suggested that the target site of tolprocarb was polyketide synthase (PKS), which regulated polyketide synthesis and pentaketide cyclization in melanin biosynthesis. Further, we produced a transgenic Aspergillus oryzae, which possessed the PKS gene of M. grisea, and performed in vitro assays of PKS using membrane fractions from the transgenic A. oryzae. Compared with some conventional melanin biosynthesis inhibitors (cMBIs), tolprocarb only inhibited PKS activity in vitro. These results indicated that tolprocarb’s target protein in M. grisea was PKS, which differentiates this fungicide from other cMBIs.

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We screened a compound library to identify chemicals that retarded plant growth. From a chemical library of 9,600 compounds, one compound (BSA-1) inhibited the hypocotyls length of Arabidopsis seedlings grown in the dark with an IC₅₀ of approximately 0.35±0.05 µM. Investigation of the mechanisms underlying the action of BSA-1 suggested that this compound inhibits neither gibberellin biosynthesis nor brassinosteroid biosynthesis. Analysis of BSA-1 analogues provided clues about structurally important features for the development of new plant growth retardants.

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The solubilization of hydrophobic organic pollutants from soil is important for the phytoremediation of contaminated soil. In this study, we used perylene as a model pollutant to evaluate the abilities of 11 organic acids to solubilize hydrophobic compounds from soil. Oxalic acid and citric acid showed high solubilization abilities, and when added to soil, they enhanced perylene uptake into Cucurbita pepo, likely owing to the chelating ability of these acids.

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Pyroxasulfone is a new herbicide developed by Kumiai Chemical Industry Co., Ltd. It has been registered in several countries for use in corn, soybeans, cotton, and wheat. Growth inhibition tests, greenhouse tests, and a field trial were conducted to evaluate the herbicidal efficacy of pyroxasulfone. Pyroxasulfone exhibited an excellent herbicidal activity at lower application rates as compared to S-metolachlor and has shown sufficient residual activity. Pyroxasulfone is one effective tool for the weed management programs.

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Strigolactones (SLs) are plant hormones that regulate various developmental phenomena over the plant life cycle. In this study, we screened the chemical library of triazole derivatives to find SL biosynthetic inhibitors and developed novel SL biosynthetic inhibitors. One of the SL biosynthetic inhibitors, TIS108, was particularly potent and reduced SL levels in planta and induced SL biosynthetic mutant-like morphology in Arabidopsis.

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Our knowledge of the ecological impact of insecticides on aquatic organisms is lacking at a community level because it requires high research skills, due to the complexity of community interactions. Here, the aquatic community’s response to the residues of two systemic insecticides, imidacloprid and fipronil, with different physicochemical properties was monitored for three years. In this study, four key points are considered for evaluating the ecological impact of the insecticides in relation to biodiversity conservation. These are as follows: (1) environmental fates as explained by their different physicochemical properties, (2) life cycles and habitats of each taxonomic and functional group, (3) indirect effects through the food chain, and (4) long-term field monitoring over the course of a year.

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Ecological properties of microorganisms involved in aerobic degradation of 2,4-D, 2,4,5-T and salithion and in anaerobic degradation of chlorophenols were examined based on their phylogenetic classification, identification and characterization of genes and enzymes, and/or distribution, diversity and succession in the soil or sediment environment by culture- and molecular-based methods. Side effects of pesticides were evaluated on the soil microbial community by analyzing community-level physiological profiles, on duckweed proliferation considering long-term exposure, recovery potential from the damage and mixture effects of the pesticides, and on river biofilm by assembling a model river biofilm.

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Pyribencarb is a novel benzylcarbamate-type fungicide against a wide range of plant pathogenic fungi, especially gray mold caused by Botrytis cinerea and stem rot caused by Sclerotinia sclerotirum. The target site of pyribencarb is cytochrome b of complex III in the electron transport system of the respiratory chain. On the other hand, the inhibitory potency of pyribencarb to the succinate-cytochrome c reductase activities of plants, rats and carp was relatively weak compared with those of strobilurin fungicides, indicating that pyribencarb is a novel Qo inhibitor of cytochrome b, whose properties are superior to the well-known Qo inhibitor fungicides in terms of selectivity and selective toxicity in the target. The inhibitory effects of pyribencarb to the cytochrome b enzyme on the transfer system of a QoI-resistant strain of B. cinerea are stronger than those of other QoI fungicides. Pyribencarb exhibited adequate control in the field experiments where QoI-resistant strains existed. This indicated that, although QoI-resistant strains develop cross-resistance against pyribencarb, as well, the extent of sensitivity reduction in QoI-resistant strains to pyribencarb was clearly lower than to other QoI fungicides. Among the QoI fungicides, pyribencarb is assumed to have unique properties. Pyribencarb belongs to the benzylcarbamate-analogue class, not the strobilurin-analogue class. Therefore, pyribencarb is thought to be a new type of QoI fungicide (BC-QoI).

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Flonicamid, a novel class insecticide possessing a unique chemical structure, was discovered in 1992, developed by Ishihara Sangyo Kaisha, Ltd., and registered in Japan in 2006 under the trade name of Ulala DF. This compound is very active against a wide range of aphid species and also is effective against some other species of sucking insects. It rapidly inhibits the feeding behavior of aphids and provides long-lasting control. Flonicamid shows no cross-resistance to conventional insecticides and exhibits excellent systemic and translaminar activity. It has no negative impact on beneficial insects and mites. Furthermore, it has a favorable toxicological, environmental and ecotoxicological profile. These characteristics make flonicamid well suited for resistant management strategies and integrated pest-management programs.

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