Journal of Pesticide Science最新文献

Plants synthesize and accumulate a wide variety of compounds called secondary metabolites. Secondary metabolites serve as chemical barriers to protect plants from pathogens and herbivores. Antimicrobial secondary metabolites are accumulated to prevent pathogen infection. These metabolites are classified into phytoalexins (induced in response to pathogen attack) and phytoanticipins (present prior to pathogen infection). The antimicrobial compounds in the grass family (Poaceae) were studied from the viewpoint of evolution. The studies were performed at three hierarchies, families, genera, and species and include the following: 1) the distribution of benzoxazinoids (Bxs) in the grass family, 2) evolutionary replacement of phytoanticipins from Bxs to hydroxycinnamic acid amide dimers in the genus Hordeum, and 3) chemodiversity of flavonoid and diterpenoid phytoalexins in rice. These studies demonstrated dynamic changes in secondary metabolism during evolution, indicating the adaptation of plants to their environment by repeating scrap-and-build cycles.

Some agrochemicals have unique activities on plant, which modes of actions differ from those of herbicides and plant growth regulators. Because these induce useful and important phenotypic characteristics by activating physiological mechanisms in plant cell, understanding the underlying mechanism of their activities should be crucial for plant physiology and agriculture. As examples of such agrochemicals, studies on agrochemicals that activate the plant immune systems or root elongation, are described. Plant activators, inducers of systemic acquired resistance, were divided into two types, acting on upstream and downstream of salicylic acid (SA) biosynthesis, respectively. They have been useful research tools to clarify the regulation mechanism of SA-mediated disease resistance and to investigate another type of disease resistance mechanism mediated by brassinosteroids. By analyzing the roles of phytohormones in the isoprothiolane-induced root elongation indicated a positive effect of jasmonic acid and ethylene on primary root elongation. These types of research, categorized to one of chemical biology, would provide novel insight into plant physiology, which also contribute to control of crops.

Crop field trials were conducted to investigate the residues of sprayed pesticides on the different sizes of tomatoes. Pesticide residue data in tomatoes varied due to different locations of the three crop fields selected and/or physicochemical properties of the three pesticides tested. The pesticide residue levels in the medium- and small-sized tomatoes were 1.5 and 2.4 times higher than the level in large-sized tomatoes under similar spray conditions, whereas amount of pesticides adhered per unit surface area were approximately equal among all three sizes of tomatoes. The results of this study suggested that the differences in pesticide residue levels were due to differences in the degree of specific surface area of each tomato size. Resultant residue data of medium-sized tomatoes demonstrated a proportional relationship between pesticide residue levels and the specific surface area of tomatoes.

The median lethal dose of pesticide in acute oral toxicity, used as a conservative index in avian risk assessment, varies by the species with differences of less than one order of magnitude, depending on body size, feeding habit, and metabolic enzyme activity. The profiles of pesticide metabolism in birds with characteristic conjugations are basically common to those in mammals, but less information is available on their relevant enzymes. The higher toxicity of some pesticides in birds than in mammals is due to the lower activity of avian metabolic enzymes. The bioaccumulation in birds is limited for very hydrophobic pesticides resistant to metabolic degradation. Several in silico approaches using the descriptors of a pesticide molecule have recently been employed to estimate the profiles of acute oral toxicity and bioaccumulation.

In order to understand the degradation of different residual pesticides of white clover silage and their influence on silage quality, three commonly used orchard pesticides with different concentrations were added to the white clover and fermented for 90 days. The results showed that the degradation rate of cypermethrin and its toxic degradation product 3-phenoxybenzoic acid (3-PBA) was the highest after silage, at different concentrations, both were 100%. The degradation rate of Tebuconazole and chloropyridine was 72.47-80.27% and 47.76-64.82%, of which 3,5,6-trichloro-2-pyridinol (TCP) content, poisonous toxic degradation product, increased 0.0525-0.253 mg·kg^-1. The residues of beta-cypermethrin and tebuconazole had reached safety standards after silage. As compared with the control, the contents of lactic acid, acetic acid, and propionic acid increased in the treated samples. The higher concentrations of three pesticides all significantly reduced the lactic acid content of silage (p<0.05). Pesticides had different effects on the nutritional components of white clover silage. Conclusively, silage is a potential way to expand the utilization of covering plants in orchards.

A new herbicide, epyrifenacil (S-3100), inhibits protoporphyrinogen oxidase (PPO) in plants. Repeated administration of epyrifenacil in laboratory animals led to some toxicological changes related to PPO inhibition, e.g., hepatotoxicity caused by porphyrin accumulation and anemia caused by the inhibition of heme biosynthesis. In vitro studies revealed that an ester-cleaved metabolite, S-3100-CA, is predominant in mammals, exhibits PPO-inhibitory activity, and thus is the cause of epyrifenacil-induced toxicity. To assess the human risk, the effects of species differences on the dynamics (PPO inhibition) and kinetics (liver uptake) of epyrifenacil were evaluated separately. The results of in vitro assays revealed an approximately tenfold weaker inhibition of PPO by S-3100-CA in humans than in rodents and six- to thirteen-fold less hepatic uptake of S-3100-CA in humans than in mice. Finally, it was suggested that humans are less sensitive to the toxicity of epyrifenacil than are rodents, although further mechanistic research is highly anticipated.

Suitable postharvest treatment methods were investigated to improve the color of grape berries. Culture solutions containing jasmonic acid (JA), methyl jasmonate (MeJA), and prohydrojasmon (PDJ) enhanced the skin coloration of grape berries ('Pione') harvested at the initial stage of coloration. MeJA vapor treatment under sealed conditions increased anthocyanin accumulation in grape berries ('AkiQueen' and 'Pione') harvested at the early stage of skin coloration. Furthermore, promoting skin coloration by MeJA vapor treatment was as effective in mature clusters as it was in detached berries. These effects were confirmed in light conditions but not in constant darkness. Our results showed that postharvest MeJA vapor treatment improved skin coloration in grapes. In addition, postharvest treatment with MeJA was found to have no effect on the endogenous abscisic acid content of grape berry skins. Therefore, we suggest that MeJA vapor treatment can be a useful and labor-saving method for the horticultural industry.

Brassinosteroids are plant steroid hormones that are essential for plant growth. When germinated rice seeds were treated with brassinolide (BL), stems were elongated and root spiral formation was observed at 5 nM of BL. Such root spiral formation was not induced by other plant hormones such as auxin and gibberellin. Since weak non-steroidal brassinolide-like compound (NSBR1) also induced spiral formation, this root spiral induction can be used as the index in the search for BL-like compounds.

We investigated the synthesis and herbicidal activity of 23 toxoflavin analogs, 1a-w, in which aromatic rings (R) were introduced into the C-3 position. In paddy field conditions, 1k (R=2-CF₃-C₆H₄) and 1w (R=2-thienyl) showed excellent herbicidal activity. Under upland field conditions, we found that toxoflavin analogs 1a (R=C₆H₅), 1n (R=2-CH₃O-C₆H₄), and 1p (R=4-CH₃O-C₆H₄) exhibited wide herbicidal spectrum against Echinochloa crus-galli (L) var. crus-galli (ECHCG), Chenopodium album, and Amaranthus viridis (AMAVI). The analog with the 2-fluoro group on benzene ring 1b also showed high herbicidal activity against both ECHCG and AMAVI.