| In recent decades,Atmospheric Pressure Low-Temperature Plasma(APLTP)has been widely used in many fields such as biomedicine,environment,material,and agriculture because of its atmospheric pressure,non-thermal and adjustable parameters.At present,due to the continuous growth of population and the continuous reduction of arable land,food shortage is becoming one of the most serious problems in the world in this century.Thus,the application of APLTP in seed decontamination,seed quality improvement,crop yield increase and plant disease control are gaining more and more attention.Although a large number of existing studies have shown that APLTP can promote plant seed germination and stimulate seedling growth,the mechanism of action of APLTP with plant cells remains unclear due to the complexity of APLTP components and the response of plant cells themselves.Therefore,this thesis takes the model plant Arabidopsis as the research object,and investigates the reactive oxygen and nitrogen species(RONS)in the gaseous and liquid state of the surface discharge plasma,and a series of biological effects of APLTP on Arabidopsis seed germination,seedling growth,cellular redox homeostasis and transcriptional level.The research work presented here can be categorized into four parts:(1)Diagnosis of the physical and chemical properties of along-plane discharge plasma and its effect on seed germination and seedling growth of Arabidopsis thaliana.In this study,the main active components of the along-surface plasma were examined by using optical emission spectroscopy(OES),high performance liquid chromatography(HPLC),attenuated total reflectance fourier transform infrared measurements(ATR-FTIR),and UV spectrophotometry.The OES results indicated that abundant excited nitrogen molecules and ion,atomic oxygen and NO existed in the air plasma,which cause an increase in the conductivity and redox potential(ORP)of the solution as well as a decrease in pH.Meanwhile,Arabidopsis seeds and seedlings(4 d)were treated with APLTP for 0.5,1,3,5,and 10 minutes,respectively,and the results of growth parameters(germination rate,primary root length,fresh weight,leaf area,number of lateral roots,number of leaves,etc.)showed a dual effect on Arabidopsis seedlings growth dependent on the treatment time.The short-time(≤3 min)APLTP treatment can enhance seedling growth and 1-min APLTP treatment shows the best stimulatory effects,while the long-time(5 and 10 min)APLTP treatment results in the growth inhibition of Arabidopsis seedlings.In addition,the SEM-EDX results indicated that the etching effects of plasma on seeds surface were dose-dependent,spanning from slight shrinkages to detached epidermis,which also significantly increased the oxidation degree of seed surface.The present results visualize the effects of APLTP treatment on germination and growth of Arabidopsis from the plant phenotype.While verifying the results of previous studies,it provides a basis for further research at the cellular level and molecular transcription level.(2)Regulation of cellular redox homeostasis in Arabidopsis seedling by APLTPgenerated reactive oxygen/nitrogen species.Research on the diagnosis and detection of APLTP active ingredients has confirmed that a large number of abundant active species are produced during the surface plasma treatment.In this thesis,the cellular redox homeostasis of Arabidopsis seedlings were investigated by measuring the active species(O2·-,·OH,H2O2,ONOO-,NO2-and NO3-)and antioxidants(GSH,AsA,GR,APX,AAO,CAT,POD and SOD)in Arabidopsis seedlings,combined with the active ingredients in the APLTP treatment solution.The results show that APLTP caused an enrichment of intracellular RONS and most of them increased with APLTP treatment time.Meanwhile,APLTP treatment accelerated MDA generation and the level of intracellular antioxidants(GSH,AsA,GR,APX,AAO,CAT,POD and SOD)were enhanced by low-dose APLTP treatment while decreased at high doses.Additionally,APLTP treatment could also evoke the accumulation of intracellular Ca2+.These results indicated that the moderate RONS generated by short-time APLTP treatment could be regarded as oxidative stimuli to improve the activities of antioxidant system and promote Arabidopsis seedling growth,while the long-time APLTP treatment would generate excessive RONS and destroy the cellular redox balance,ultimately causing oxidative stress and inhibiting seedling growth.This study systematically investigates the regulation mechanism of APLTP-generated RONS on intracellular redox homeostasis in Arabidopsis seedlings by measuring the RONS compositions in APLTPtreated solutions and intracellular RONS and antioxidants in Arabidopsis seedlings.(3)Comparative transcriptome analysis of Atmospheric pressure low-temperature plasma enhanced early seedling growth in Arabidopsis.Based on the above results,1min APLTP treatment apparently exhibited the maximal beneficial effects on the early growth of Arabidopsis seedlings.Thus,1-min APLTP treatment was chosen as the optimum regime to investigate the transcriptome changes of APLTP-induced stimulatory effects on seedling growth.The RNA-Seq analysis showed that a total of 218 differentially expressed genes(DEGs)were identified in 1-min APLTP-treated seedlings vs.the control,including 20 up-regulated and 198 down-regulated genes.The DEGs were enriched in pathways related to glutathione(GSH)metabolism,mitogenactivated protein kinase(MAPK)signaling transduction and plant resistance against pathogens.The metabolic analysis of amino acid,GSH and phytohormone demonstrated that 1-min APLTP treatment decreased most amino acids concentrations in Arabidopsis seedling,while the accumulation of GSH,gibberellins and cytokinin were significantly increased.These results indicated that the moderate APLTP treatment may regulate the expression of stimuli/stress-responsive genes involved in GSH,phytohormone/amino metabolism and plant defense against pathogens via MAPK signal transduction pathway,accordingly enhance Arabidopsis seedling growth.The above research results will provide theoretical support for the study of the biological effects of low-temperature plasma on other complex crops,and provide a scientific basis for improving the mechanism of low-temperature plasma and plant cells,thereby promoting the popularization and application of APLTP in agricultural production. |
