Study On The Absorption And Transport Mechanisms Of Typical Pesticides In Rice

With the improvement of people’s quality of life requirements,the quality and safety of agricultural products are receiving increasing attention.The residual pesticides in the environment were absorbed by crops and enriched in various tissues,and even accumulated in large quantities in the edible parts,leading to a decline in the quality of agricultural products and a threat to their safety.The direct absorption of pesticides by crops from the environment is one of the main sources of pesticide residues in agricultural products.Therefore,analyzing the absorption and transport mechanisms of pesticides by crops is of great significance for controlling pesticide residues and ensuring the safety of agricultural products.Starting from the concept of pesticide residue control,this study focuses on the widely planted crop rice.Through indoor hydroponic experiments,explored the enrichment dynamics,subcellular distribution,and transmembrane absorption patterns of different classes of pesticides in rice roots,stems,and leaves,clarified the residual behavior and influencing factors of pesticides in various tissues of rice,and provided a theoretical basis for controlling the absorption and transfer process of pesticides to ensure the quality and safety of agricultural products.In this paper,three classes of typical pesticides were selected:neonicotinoids(thiamethoxam,imidacloprid,acetamiprid,nitenpyram,thiacloprid,clothianidin,and dinotefuran,-0.66<log K_ow<1.26);triazole fungicides(triadimefon,myclobutanil,propiconazole,flusilazole,epoxiconazole,difenoconazole,and hexaconazole,2.77<log K_ow<4.4)and sulfonylurea herbicides(tribenuron-methyl,chlorsulfuron,nicosulfuron,pyrazosulfuron-ethyl,chlorimuron-ethyl,ethoxysulfuron,and rimsulfuron,-1.47<log K_ow<2.89)were studied,and the main results are as follows:（1）Through indoor hydroponic experiments and quantitative analysis of pesticide content in rice roots,stems,leaves,and nutrient solutions using HPLC-MS/MS,it was found that rice accelerated the degradation of pesticides in nutrient solutions,with significant differences in the half-life of different classes of pesticides.The half-life of all neonicotinoids were smaller than that of triazoles,and the half-life of different sulfonylureas varies greatly.The time for pesticides to reach absorption equilibrium increased with the enhancement of hydrophobicity.Neonicotinoids were mainly concentrated in the leaves of rice,while triazoles were mainly concentrated in the roots of rice.The octanol coefficient(log K_ow),molecular weight（MW）,solubility（SW）and molecular structure of pesticides were the key factors affecting the absorption and transport of different classes of pesticides.The enrichment and transport of neonicotinoids in rice roots,stems,and leaves were mainly influenced by log K_ow and SW,and were not related to MW.The enrichment and transport of triazole pesticides in roots,stems,and leaves were mainly influenced by log K_ow and MW,and were not related to SW.In the design and development of new pesticides,the enrichment efficiency of pesticides in plants is improved by enhancing the electronegativity of atoms and van der Waals volume,and the transfer efficiency of pesticides from underground to above is improved by enhancing the sum of heteroatom topological state index and the maximum positive charge on nitrogen atoms,so as to reduce pesticide residues in the environment,avoid secondary enrichment,and thus reduce residues in rice grains.（2）The subcellular distribution trend of the same class of pesticide in rice root,stem and leaf is the same,and the distribution proportion of cell wall,organelle,cell soluble fraction and apoplast component was highly positive correlation between two tissues（root and stem,stem and leaf,root and leaf）.Neonicotinoids were more concentrated in symplasts,intracellular and liquid components,especially in soluble fractions;Triazoles were mainly concentrated in the symplasts,extracellular and solid phase components,mainly in the cell walls;Sulfonylureas were more concentrated in the apoplasts of extracellular space.The enrichment and transport of pesticides were correlated with the proportion of subcellular distribution:the enrichment in roots was positively correlated with the enrichment coefficient of cell walls,and the enrichment in stems was positively correlated with the enrichment coefficient of organelles.The transfer coefficient of pesticides from stems to leaves decreases with the increase of the enrichment coefficient of organelles in roots,stems and leaves.（3）Through indoor hydroponic culture combined with different inhibitor experiments,it was found that different classes of pesticides have different transmembrane absorption patterns:the absorption of neonicotinoids by rice was a process mediated by water channel proteins and anion channels,and most of it was an active process that required energy consumption.The absorption of triazole pesticides by rice was a passive process that does not require the participation of aquaporins and anion channels.