Absorption,Translocation,Accumulation And Metabolism Of ¹⁴C-Benzene Kresoxim-methyl In The Cucumber (Cucumis Sativus.L)

Based on the active group?-methoxyacrylate,Strobilurin fungicide is one kind of respiratory inhibitors.Strobilurin has a unique mechanism of action compared to other commercial fungicides.Consequently,strobilurin shows highly efficient and broad-spectrum antifungal activity that can prevent many diseases.However,the long-term worldwide use of strobilurin has resulted in the emergence of several pathogens with resistance to the fungicide.Moreover,strobilurin has potential adverse effects on the ecosystem,non-target organisms,and human health.Thus,there is an extremely urgent need to develop new chemicals to permit extending the application life of strobilurin,while delaying the development of drug resistance in the target pathogens and minimizing non-target effects.Field experiments showed that benzene kresoxim-methyl(BKM)had high fungicidal activity to against a variety of plant diseases,and the required field application amount was significantly less than that of similar fungicides,which had a good market foreground and development prospect.However,its behavior and fate in the registered crop plant cucumber remains unknown.This research took the BKM as the research object and comprehensively used the isotope tracer technology and advanced instrument analysis technology.This study focused on the absorption,translocation,accumulation and metabolism of the BKM in cucumber plants.This research is aim to provide a theoretical basis and data support for more objective assessment and scientific understanding of the environmental safety of BKM.Our results can be incorporated into regular assessments of BKM in food safety and help guide agricultural use.It also provides a reference research ideas and technology systems for other innovative drug research with independent intellectual property rights in China.The main results obtained were as follows:(1)The absorption,translocation and accumulation of two formulations ¹⁴C-BKM in the cucumber plants at three leaf stage.After 480 h of the application,28.2%(SC)and 31.2%(EC)of ¹⁴C-BKM were absorbed into the three leaf stage cucumber plants,and the majority of ¹⁴C-BKM was accumulated in labeled leaves.The subcellular distribution experiment of the labeled leaves showed that cell wall was the main storage site of ¹⁴C-BKM.The results showed that the uptake of difenoconate in the two formulations could be translocated in both directions and distributed in all parts of the plant systematically.The accumulation of¹⁴C-BKM in the leaves above the labeled leaves was significantly higher than that in the leaves below the labeled leaves,indicating that ¹⁴C-BKM was more easily transported to the top.The residue and concentration of SC BKM in all parts of the plant were significantly higher than that in EC BKM,which shows that SC BKM was more environmentally safe and friendly.(2)The absorption,translocation and accumulation of ¹⁴C-BKM in the mature cucumber plants.In the vegetative organs of mature cucumber plants,more than 80%of the ¹⁴C-BKM accumulated in the labeled leaves and was not easy to be transported to other plant organs.The order of residual concentration in each vegetative organ was:the labeled leaves>the lower part of the stems>newborn leaves>the upper part of the stems>roots.The total accumulation of ¹⁴C-BKM in the reproductive organs was significantly lower than that in the vegetative organs,and mainly distributed in labeled fruits.The highest residue concentration of ¹⁴C-BKM in the pericarp of the labeled fruit was 1.3 mg kg^-1,while the residue concentration in the sarcocarp of the labeled fruit was not higher than 0.027 mg kg^-1;the accumulation of ¹⁴C-BKM in the newborn fruits were extremely low,that the highest residual concentration was only 0.005 mg kg^-1.The EDI of BKM in the cucumber fruit was 0.0017 mg(kg bw)^-1 day^-1,which was far below its ADI(0.1 mg(kg bw)^-1 day^-1),indicating that the dietary risk of cucumber fruit treated with BKM at the recommended application dose was low.(3)The residue,product composition and metabolic pathway of ¹⁴C-BKM in the mature cucumber plants.The bound residues(BR)of ¹⁴C-BKM in the labeled leaves,pericarp and sarcocarp of the labeled fruits in the mature cucumber plants increased with time,while the extractable residues(ER)decreased with time,and the final ER in these parts followed the order of the pericarp of the labeled fruits>the labeled leaves>the sarcocarp of the labeled fruits.The half-life of BKM in labeled leaves,pericarp and sarcocarp were 14days,11 days and 10 days,respectively.Seven metabolites were identified by analyzing the ER composition of ¹⁴C-BKM:the partent BKM,acid BKM(BKM-M1),hydroxylated BKM(BKM-M2),ethylated BKM(BKM-M3),demethylated hydroxylated BKM(BKM-M4),glucose and BKM glycoconjugate(BKM-M5),hydroxyacetylation BKM(BKM-M6).Five metabolites were found in the sarcarp of the labeled fruits:the partent BKM,BKM-M1,BKM-M2,BKM-M5 and BKM-M6,and the maximum residue concentration of the metabolites was only 0.012?g g^-1,which was far lower than the residue limit standard.And all seven metabolites were found in the labeled leaves and the pericarp of the labeled fruits.According to the proportion of residue amount and the highest residue concentration,the residue of BKM in labeled leaves of the mature cucumber plants was defined as the parent,and the residue of BKM in pericarp of the labeled fruits of the mature cucumber plants was defined as the parent,BKM-M1 and BKM-M2.According to the dynamic amounts of the metabolites and the chemical structures,the possible metabolic pathways of BKM in cucumber plant were speculated,including the phase I metabolism and the phase II metabolism.Metabolic pathway 1:first,parent BKM can form metabolite BKM-M1 by demethylation;then,BKM-M1 reacts with ethanol to form the metabolite BKM-M3,finally,BKM-M3 can demethylate to form metabolite BKM-M4.Metabolic pathway 2:first,parent BKM can form metabolite BKM-M2 by hydroxylation reaction;then,the conjugation reaction of BKM-M2 with a molecule of glucose forms the metabolite BKM-M5.Metabolic pathway 3:the hydroxyl group of BKM-M2 can be acetylated and demethylated to form the metabolite BKM-M6.