Uptake,Translocation,Subcellular Distribution And Relevant Molecular Docking Of Mecopron Enantiomers In Arabidopsis Thaliana

Mecoprop(MCPP)is a kind of commonly used chiral auxin herbicide.With the increased recognition of chiral pesticides and relevant mechanism,some research reported that the enantiomers of chiral MCPP exhibits significant herbicidal enantioselectivity in target dicotyledon,R-structure of MCPP possess significant herbicidal activity which S-structure cannot catch up with.In order to figure out the main reason of the disparity,we built the method and carried on experiments with two perspectives:Firstly we explored the absorption,transportation and distribution on the subcellular level of MCPP enantiomers in Arabidopsis thaliana,and then we utilized molecular docking method and homology modeling(way of constructing new protein structure)included in Computer-aided Drug Design to research and predict the binding strength and states about target proteins and corresponding MCPP enantiomers with the aim of exploring the enantioselective disparity on the combining level of ligand-receptor interaction.We carried on this with experiments about absorption and transportation for the sake of probing the disparity of drug metabolism and bio-signal transduction that stereo-structure of chiral pesticides conducts,thus we can provide reference for the development of new herbicides and recognition of related herbicidal metabolism.The results are presented as follow:i.Research about absorption,transportation,subcellular distribution of 14C-MCPP enantiomers with the support of 14C tracing method in Arabidopsis thaliana reveal that:The absorption of MCPP enantiomers in Arabidopsis thaliana are listed as follow:R-MCPP(90.45±0.25)%,S-MCPP(85.75±0.74)%.The difference is significant.After application,both enantiomers of MCPP tend to transport downward,and R-MCPP is inclined to translocate slower and more persistent than S-MCPP.Compared with S-MCPP,the transportation ratio of R-MCPP tends to rank higher.Once being transported downward from the labeled leaves,the ratio of R-MCPP(6.00%±0.56%)is 1.5 times higher than that of S-DCPP(2.14%±0.13%).As for subcellular distribution,the ratio of MCPP in cytoplasm ranks top among the distribution ratio of two MCPP enantiomers,then goes the ratio in cytoderm and the ratio in organelle is lowest.When approaching to equilibrium state,the distribution ratio of S-MCPP in cytoderm(39.60%±0.62%)is higher than that in R-MCPP(28.74%±0.88%),elucidating that the cytoderm keeps better fixation of S-MCPP than R-MCPP.While in organelle,the distribution ratio of R-MCPP(10.55%±0.50%)comes higher than that in S-MCPP(4.11%±0.46%).According to the fact that target proteins of MCPP are usually located in the organelle,R-MCPP is easier to get access with target proteins than S-MCPP.ii.The relevant protein receptors of auxin herbicides,including MCPP are TIR1 and AFBs.So we select TIR1(the main receptor of IAA)and AFB2(collateral homologous protein of TIR1,main receptor of IAA as well)as subjects for molecular docking experiment.First of all,we built the structure of AFB2 with homology modeling method.Some modeling assess tools,like Ramanchandran Plot and ERRAT reveal that the structure is reasonable and stable.Then we dock R/S-MCPP separately with TIR1 and AFB2 for predicting both binding strength and binding states with Glide mode and Docking Score/Glide Emodel as the marking criterion.The docking result indicates that in the docking procedure of S-MCPP and TIR1,the methyl on the chiral carbon atom meets hindrance formed by Leucine-rich hydrophobic walls,leading to the result that the rotation penalty of S-MCPP is higher than that of R-MCPP.The hydrophobic enclosure and H-bond affinity of R-MCPP are better than that of S-MCPP,so in general the docking score of S-MCPP is lower than the score of R-MCPP.As for the result of binding to AFB2,the gap of docking results are more significant,both in Glide Emodel and in Docking Score.R-MCPP gets higher score both in Docking Score and Glide Emodel,reflected in the result that R-MCPP gets more score in the evaluation event of lipotropism and Van der Waal interaction.