Nocardioides sp. PD653 genes hcbA1, hcbA2, and hcbA3 encode enzymes that catalyze the oxidative dehalogenation of hexachlorobenzene (HCB), which is one of the most recalcitrant persistent organic pollutants (POPs). In this study, HcbA1, HcbA2, and HcbA3 were heterologously expressed and characterized. Among the flavin species tested, HcbA3 showed the highest affinity for FMN with a Kd value of 0.75±0.17 µM. Kinetic assays revealed that HcbA3 followed a ping-pong bi–bi mechanism for the reduction of flavins. The Km for NADH and FMN was 51.66±11.58 µM and 4.43±0.69 µM, respectively. For both NADH and FMN, the Vmax and kcat were 2.21±0.86 µM and 66.74±5.91 sec−1, respectively. We also successfully reconstituted the oxidative dehalogenase reaction in vitro, which consisted of HcbA1, HcbA3, FMN, and NADH, suggesting that HcbA3 may be the partner reductase component for HcbA1 in Nocardioides sp. PD653.
Mandestrobin is a novel and potent fungicide with a methoxyacetamide structure, and inhibits complex III on the mitochondrial respiratory chain of fungi. It is widely accepted that some fungicides, including QOIs and SDHIs, have additional physiological effects on treated plants. In this study, we evaluated the physiological effects of mandestrobin both in the field and the laboratory. Mandestrobin treatment increased the yield of Brassica napus by an average of 6.3% in the field under disease-free conditions. Mandestrobin treatment delayed chlorophyll degradation and the senescence of B. napus leaf discs, and excised Arabidopsis thaliana leaves in darkness. Analyses of transcriptome and gene ontology enrichment of mandestrobin-upregulated genes showed that chlorophyll degradation genes and jasmonate-related genes were downregulated while salicylate-related genes were upregulated by mandestrobin treatment. A possible mechanism by which mandestrobin triggered the physiological effects observed in the field and the laboratory was discussed.
The metabolic fate of esfenvalerate (1), 14C-labeled at the chlorophenyl or phenoxyphenyl ring, in tomato plants was investigated by spraying it three times at 15 g/ha. The overall metabolic trend of 1 was similar in foliage and fruit. The applied 1 gradually penetrated into the foliage/fruit, and approximately 30% of the total radioactive residue (TRR) distributed within the plant. The applied radioactivity remained mostly intact on the plant surface, while its degradation proceeded via ester cleavage to produce two corresponding acids derived from the chlorophenyl and phenoxyphenyl moieties, followed by saccharide conjugation at the inner tissues (each <5%TRR). While 1 retained its optical configuration (2S,αS) on the plant surface and in the fruit, a very slight isomerization at the α-cyanobenzyl carbon occurred to form a (2S,αR) isomer in the foliage (≤1%TRR). The isomerization at another asymmetric carbon C2 in the isovaleric acid moiety did not proceed on/in the plant for 1 or its metabolite.
Increasing numbers of azole-resistant Aspergillus fumigatus (ARAf) in the environment have become a global public health issue. We surveyed tulip bulbs that were imported from the Netherlands and found that 6.3–15.8% of bulbs were contaminated by ARAf with a tandem-repeat mutation in the promoter region of the cyp51A gene. We also showed that fungicide treatment of the tulip bulbs by benomyl or prochloraz effectively reduced the rate of isolation. This is the first report demonstrating a method of eliminating human fungal pathogens from plant bulbs.
Water milfoil is a sediment-rooted macrophyte contributing to the aquatic ecosystem, and the risk evaluation of pesticides on this new assessment species has attracted much attention. Knowledge of the shoot/root uptake, inner-plant translocation, and the metabolism of pesticides in water milfoil is essential for a detailed risk assessment and understanding toxicological mechanisms thereof; however, the behaviors have not been studied in detail. Using model studies, the author clarified shoot and root uptake dynamics of 3-phenoxybenzoic acid via water and sediment exposure, respectively, followed by transportation and metabolism at each plant portion; uptake and metabolism kinetics of simple phenols amended with regression analysis on physico-chemical parameters of the compounds; detailed metabolic fate of flumioxazin in various aquatic plants/phytoplankton, and an interspecies comparison. Similar approaches are fully applicable to clarifying the fate of pesticides in water milfoil and are expected to be useful for implementing advanced risk characterizations.
To estimate pesticide residue levels in succeeding crops based on those in soils, the relationship between pesticide concentrations in komatsuna (Brassica rapa var. perviridis) and the concentrations extracted sequentially from soils using water and acetone was investigated. The concentrations of many pesticides in komatsuna shoots showed higher positive correlation with water-extractable concentrations (CW) than total-extractable concentrations in soils, so that the CW was available for evaluating the phytoavailability of pesticides in the soil. As a result of examining the dissipation behavior of the CW, the dissipation of the CW was able to be predicted by considering time-dependent soil sorption, which could be estimated using the sorption coefficients (Kd) measured by a standard batch method. Furthermore, the present study showed that the properties of soil organic carbon such as black carbon content and the molecular structure of pesticides were important for estimating the Kd values more accurately.
Investigation of the dissipation and transformation of pesticide through laboratory experiments, conducted in accordance with standard and newly developed designs, gives us valuable information to understand their environmental behavior. We have also been investigating the mechanisms of partition and transformation reactions of pesticides, not only through kinetic analyses, but also through theoretical approaches based on their molecular properties estimated using various spectroscopies and molecular orbital calculations. Furthermore, synthetic iron porphyrin with a peroxide was shown to be a good model to simulate the P450-catalyzed oxidation in the metabolism of pesticides. Through these investigations, the knowledge of surface water, soil, sediment, and plants, such as their properties and constituents, was found indispensable to a deep understanding of the mechanism in the hydrolysis, photolysis, and metabolism of pesticides.
Natural product research, including total synthesis, is becoming increasingly important for the discovery of pesticide seeds and leads. Synthetic studies of biologically active compounds such as antibiotics (enacyloxins, polynactin, pamamycins, spirofungin A and B, glutarimides and antimycins), phytopathogenic toxins (pyricuol, pyriculariol, tabtoxinine-β-lactam, gigantenone, phomenone and phaseolinone), marine derived products (pteroenone, β-D-Asp-Gly, didemniselinolipid B, cortistatin A, sanctolide A and gizzerosine), POPs (dieldrin, endosulfan, HCB), plant hormones (abscisic acid and jasmonic acid), insect pheromones (endo-brevicomin etc.), especially using a variety of biotransformation are described.
Pyraziflumid is a novel succinate dehydrogenase inhibitor (SDHI) fungicide discovered and developed by Nihon Nohyaku Co., Ltd. It exhibits excellent fungicidal activities against a broad range of plant diseases and has a favorable safety profile for the Integrated Pest Management (IPM) program. This compound was found by researching the unique chemical derivatives, 3-(trifluoromethyl)pyrazine-2-carboxamides, and has good biological properties, such as preventive, residual and curative activity, and rain-fastness. Pyraziflumid was registered and launched in Japan in 2018. It was registered in South Korea in 2018 and is now under development in other countries. This paper describes the discovery, synthesis, biological activity, safety profile and mode of action of pyraziflumid.