We investigated the behavior of isoprothiolane and fipronil after nursery-box application and that of isoprothiolane after submerged application in an experimental paddy field. The concentrations of the pesticides and their metabolites were monitored in paddy water, soil, and rice plants. The distribution profile for isoprothiolane mass in the field differed greatly between the nursery-box and submerged applications. The nursery-box-applied pesticides were mostly distributed in soil near the transplanted rice seedlings (root zone), versus little distribution in paddy water and rice plants (<1.1 and <0.3% of the applied mass, respectively). The residual levels in rice plants were similar to those in the root-zone soil. To estimate the soil pesticide mass, we defined a key parameter: the ratio of the root-zone area to the total area of the paddy field estimated to be 0.1 to 0.15. This parameter is important when evaluating the concentrations of nursery-box-applied pesticides in soil and rice plants.
We developed an improved version of the PADDY model for predicting pesticide behavior in paddy fields, which includes pesticide uptake by rice roots. We applied the model to nursery-box and submerged pesticide applications. A paddy field was divided into root-zone and inter-plant areas, and paddy soil containing pesticides was vertically separated into three layers. Pesticide behavior was modeled with mass fractions of the pesticides in paddy water and the soil layers immediately after rice transplanting obtained from field experiments, and uptake by rice roots was described using the transpiration stream concentration factor. The improved model successfully simulated measured concentration changes in a paddy field, including rice plants, under nursery-box and submerged applications. The model evaluated the difference in the concentrations of nursery-box-applied pesticides between root-zone and inter-plant soil samples with several key parameters. Our study provides a useful solution for simulating the uptake of pesticides in soil by rice roots.
The agricultural fungicide procymidone can cause external genitalia abnormalities in rats but not monkeys or rabbits. To investigate the relevance of developmental findings in rats to humans, we conducted in vitro plasma protein binding studies, in vitro metabolism (biotransformation) studies using liver S9 fractions and hepatocytes, and in vivo metabolism and excretion studies using chimeric mice with humanized hepatocytes. On the basis of these results, we concluded that the metabolic and excretion profiles of procymidone in humans are similar to those in monkeys and rabbits but differ from those in rats. From the findings of this and previous studies, we judge the developmental toxicity potential of procymidone to be very low in humans.
While pcp genes are well known in Gram-negative bacteria to code for the enzymes responsible for pentachlorophenol (C6HCl5O; PCP) degradation, little is known about PCP-degrading genes in Gram-positive bacteria. Here we describe a novel gene operon possibly responsible for catalyzing the degradation of PCP in the Gram-positive bacterium Nocardioides sp. strain PD653, which is capable of mineralizing hexachlorobenzene (C6Cl6; HCB) via PCP. Transcriptome analysis based on RNA-Seq revealed overexpressed genes in strain PD653 following exposure to HCB. Based on in silico annotation, three open reading frames (ORFs) were selected as biodegrading enzyme candidates. Recombinant E. coli cells expressing candidate genes degraded approximately 9.4 µmol L－1 PCP in 2 hr. Therefore, we designated these genes as hcbB1, hcbB2, and hcbB3. Interestingly, PCP-degrading activity was recorded when hcbB3 was coexpressed with hcbB1 or hcbB2, and the function of HcbB3 was expected to be similar to chlorophenol 4-monooxygenase (TftD).
Strigolactones (SLs) are a series of sesquiterpene lactones that serve as plant hormones to regulate plant growth and development, such as shoot branching, lateral root formation, and root hair elongation. Recently, SLs have been reported to accelerate the leaf senescence, which is also regulated by sugar signals. In this study, we utilized segments of a bamboo leaf to observe leaf senescence and confirmed that SL accelerates leaf senescence and triggers cell death under a dark condition rather than under a light condition. Further studies showed that the co-treatment of sugars suppressed SL-induced leaf senescence and cell death under dark conditions, suggesting a crosstalk between SL and the sugar signal in regulating leaf senescence.
To clarify species differences in the developmental toxicity of procymidone (Sumilex®, a fungicide for agricultural use), placental transfer studies were conducted using 14C-labeled procymidone in pregnant rats, rabbits, and monkeys. These studies demonstrated that maternal-to-fetal transfer of the parent compound and its hydroxylated metabolite, which are both weak anti-androgenic agents, occurred more easily than that of other metabolites, with much higher absolute concentrations achieved in the fetal circulation of rats than of rabbits or monkeys. Notably, in rats, the fetal plasma concentration of the hydroxylated metabolite was higher than that of procymidone, especially after repeated oral administration of procymidone. These results suggest that the hydroxylated metabolite is the most relevant metabolite involved in teratogenic activity in rats.
Photodegradation is one of the most important abiotic transformations for pesticides in the aquatic environment, and the high energy of sunlight causes characteristic reactions such as bond scission, cyclization, and rearrangement, which are scarcely observed in hydrolysis and microbial degradation. This review deals with direct photolysis via excitation of a pesticide by absorbing natural or artificial sunlight in order to know its basic photochemistry, and indirect photolysis meaning either sensitization by dissolved organic matters or oxidation by reactive oxygen species is basically excluded. Several experimental approaches including spectroscopic techniques together with theoretical calculations are first discussed from the viewpoint of the reaction mechanisms in direct photolysis. Then, the typical photoreactions of pesticides are summarized by chemical classes and/or functional groups and discussed as far as possible in relation to their mechanisms.
Efficiency of caffeic acid (CA) on Spodoptera littoralis was investigated. CA was mixed with artificial diet, and feeding indices and allatostatin-A (AST-A) content of the midgut were measured 10 days later. α-Amylase and protease activities were evaluated for 10 days. CA significantly decreased feeding indices. Feeding on an artificial diet containing CA decreased protease and α-amylase activities in the midgut. The incubation of the dissected midgut with AST-A increased α-amylase and protease activities. The injection of AST-A into the hemolymph of larvae also increased protease and α-amylase activities. Competitive ELISA and immunohistochemistry results showed that starvation decreased the AST-A titer and AST-A immunoreactivity (AST-A-ir) cells in the midgut whereas refeeding increased it. Here, for the first time we showed that feeding on an artificial diet containing CA also caused the AST-A level to decrease in the midgut, which itself caused α-amylase and protease activities to decrease.
We performed uptake experiments with 12 different organic chemicals using 16 plant species and determined differences in the ability of plant species to take up and translocate these chemicals. There were differences among the plant species in the shoot and root concentrations of each organic chemical. The root concentration factor values increased with an increasing log of the n-octanol–water partition coefficient (log KOW) of organic chemicals. Thus, the concentrations in roots may be predicted to a certain extent because the root concentration factor values were related to the log KOW. The root-to-shoot translocation was related to the log KOW because the shoot-to-root concentration ratio decreased with an increasing log KOW; however, there was no clear relationship between the shoot concentration factor value and the log KOW, and this differed among plant species.
In view of the possibility that spent mushroom substrates (SMSs) may be used as agricultural materials to prevent crop diseases, we examined the effect of treatment with a hot water extract from the SMS of Lentinula edodes on plant resistance to pathogenic infection. The extract of Le. edodes SMS was sprayed onto the leaves of rice plants, followed by inoculation of the leaves with the conidia of rice blast fungus. The development of lesions was suppressed by treatment with the SMS extract. The extract markedly inhibited the germination of Pyricularia oryzae conidia. We purified compounds 1, 2, and 3, which showed inhibitory effects on conidial germination, from the Le. edodes SMS extract of by successive solvent extraction, column chromatography, and preparative HPLC. Spectroscopic analyses revealed that 1, 2, and 3 were phenolic acids with two carboxyl groups in common.
In our research, a series of 8-substituted coumarin derivatives were synthesized, and their structures were confirmed by FT-IR, 1H-NMR, and MS (or HRMS). In activity screening, the synthesized compounds exhibited potent antifungal activity against 4 phytopathogenic fungi: Botrytis cinerea, Colletotrichum gloeosporioides, Fusarium oxysporum, and Valsa mali. Notably, 8-chloro coumarin and ethyl 8-chloro-coumarin-3-carboxylate showed the strongest fungus inhibition with EC50 of 0.085 and 0.078 mmol/L against V. mali. Furthermore, 3D-QSAR models (CoMFA and CoMSIA) of the title compounds against V. mali were established on the basis of their antifungal activities. The results indicated that the appropriate small, hydrophilic and electron-withdrawing groups on coumarin’s C-3 and C-8, respectively, could enhance the antifungal activity. The information obtained will be very helpful for designing new derivatives with high antifungal activities.