Effect Of Chemical Pesticides On Plant Tissues And Rhizospheric Environment

Pesticides are an important means to ensure a good agricultural harvest.Long-term repeated use causes a large amount of pesticides to remain in the farmland environment.The pesticides remaining in the soil and water are easy to migrate to non-target crops,which further affects the physiological metabolism of plants and the rhizosphere environment.However,the research on the mechanism of pesticide-plant-rhizosphere interaction is relatively scarce.Metabolomics is a discipline that studies the types and quantities of endogenous metabolites in organisms and their changing laws under the action of internal and external factors.Metabolomics has become a powerful tool for studying unpredictable metabolism.It can clarify the differences in biological tissues at the molecular level under different processes kind of reaction.Therefore,this project aimed at the research on the effect of chemical pesticides on plant tissues and rhizosphere microorganisms based on metabonomics and microbiology.The research results will provide an important basis for assessing the potential impact of pesticides on the environment.The main content and results are as follows:(1)In the second chapter,the effects of three pesticide on plant shoots were investigated using the non-targeted metabonomics technology.The pesticides being sprayed on plant tissues included insecticide thiamethoxam,fungicide tebuconazole and herbicide acetochlor,and the recommended dosage of the three pesticides for vegetables was chosen.The experimental results show that the spraying of three different pesticides has a certain effect on the physiological metabolism of vegetables;however,there are certain differences in the effects of different pesticides on plants.When treated with the insecticide thiamethoxam,the amino acids,nucleic acids,flavonoids and phenolic acids in the leaves of the vegetable were significantly accumulated.The metabolic pathway of C5-branched dibasic acid was significantly affected by thiamethoxam.Under the tebuconazole treatment,the content of amino acids,sugars and phenolic acids in the plant were down-regulated.Under acetochlor treatment,the content of sugars and flavonoids in the vegetable leaves was significantly down-regulated,and fatty acids were significantly up-regulated.Metabolic pathway of glyoxylic acid and dicarboxylic acid esters was significantly affected by acetochlor.In addition,Three different pesticides also significantly affected the pathways of tricarboxylic acid cycle(TCA cycle),and nicotinic acid ester and nicotinamide metabolism.(2)In the third chapter,liquid chromatography-tandem quadrupole mass spectrometry(LC-QTOF/MS)was used to investigat the effect of dinotefuran on root exudates of Chinese cabbage(Brassica rapa var.chinensis).The physiological activities revealed that dinotefuran uptake caused oxidative stress in vegetable tissues even at low dinotefuran exposure levels.The metabolic profile of plant root exudates acquired by LC-QTOF/MS was clearly changed by dinotefuran,where the numbers of both up-and down-regulated MS peaks increased with increasing dinotefuran concentration.Under dinotefuran stress,some osmotic adjustment substances(proline and betaine)and defence-related metabolites(spermidine,phenylalanine and some phenolic acids)were significantly upregulated,which may help plants adapt to adverse environmental conditions.Specifically,the contents of some phenylalanine-derived secondary metabolites increased with increasing of dinotefuran concentration,which may increase the external detoxification ability of plants.Moreover,respiration metabolism was significantly affected,where some intermediates in the TCA cycle(succinic acid and malic acid)were upregulated with low-level dinotefuran exposure;however,anaerobic respiration products(lactic acid and 3-phenyllactic acid)were accumulated at high exposure levels.In addition,the release of glucosinolates was significantly inhibited in both dinotefuran treatment groups.(3)In the fourth chapter,the effect of imidacloprid on the plant root exudates and rhizosphere soil microflora was studied based on metabolomics combined with microbiology.Metabolomics analysis found that imidacloprid can significantly affect the secretions of vegetable root exudates,59 different metabolites were detected,most of the metabolites were up-regulated(23.4% up-regulation for low-concentration treatment,26.1% up-regulation for high-concentration treatment),in which the content of amino acids and organic acids both increased with increasing of imidacloprid.The analysis of the bacterial diversity of rhizosphere soil by 16 S r RNA gene sequencing technology found that the Shanno index and ACE index of rhizosphere soil bacteria increased with increasing of the imidacloprid concentration,indicating that imidacloprid could affect the abundance and diversity of rhizosphere bacteria.The abundance of bacteria associated with the nitrogen cycle,has increased significantly under imidacloprid treatments.Correlation analysis showed that most of the microbial OUT in the rhizosphere was significantly related to various substances in root exudates,especially amino acids,organic acids and lipids.The abundance of imidacloprid degrading bacteria Ramlibacter in rhizosphere soil increased with the increase of imidacloprid concentration.The function prediction using Tax4 Fun shows that the amino acid metabolism of rhizosphere bacteria,the biosynthesis of other secondary metabolites and the metabolism of cofactors and vitamins are also significantly positively correlated with related substances in root exudates.