Studies On The Mechanisms Of Growth Stimulation And Enhanced Stress Tolerance Induced By Carbon Ion Beams Irradiation In Arabidopsis Thaliana

Heavy ion beam has become an emerging mutagenesis breeding method due to its unique physical and biological characteristics.Compared with X-ray and gamma rays,heavy ion beam has the following characteristics:?1?Higher energy transfer per unit length track,higher Linear energy transfer density?LET?and higher biological efficiency.?2?Bragg peak leads to relatively dense damage in the center of the track of irradiated material,but has little effect on the parts beyond the irradiated position.The total mutation efficiency caused by relatively high Relative biological effectiveness?RBE?is about 20 times higher than that of the common electron beam.Apart this,the probability of chromosome fragment rearrangement and point mutation induced by heavy ion beam is 14 times and 13 times higher than that of the common electron beam.Studies have shown that plant cell structure,external morphology,physiology,biochemistry and molecular mechanism were all affected by ion irradiation in varying degrees.In addition,low-dose ionizing irradiation can stimulate organisms,namely radiation excitation effect,which has been proved in different biological species.In recent years,the stimulation effect of low-dose heavy ion irradiation on the growth and development of different organisms has been reported successively.In addition,a large number of studies also found that low-dose ionizing irradiation can alleviate the damage to plants caused by abiotic stress under adverse conditions,so as to improve the stress resistance of plants.However,the research on the growth stimulation effect and stress resistance enhancement mechanism of carbon ion beams irradiated plants is very limited.In this study,Arabidopsis thaliana seeds were irradiated with 0,50,100,150 and200 Gy doses of carbon ion beams irradiation.The germination index of seeds,growth and development of seedlings and plants,structure change of seed coat,physiological and biochemical indexes and expression of related genes were statistically analyzed under different doses of carbon ion beams irradiation treatment,to explore the physiological,biochemical,cytological and molecular mechanism of the stimulation effect of low doses of carbon ion beams irradiation on the growth and development of Arabidopsis thaliana.Transcriptome database was established by transcriptome sequencing analysis control and low dose irradiated samples,revealing the metabolic pathways and transcription factors that play an important role in the growth and development of plants with low dose carbon ion beams irradiation.The physiological indexes and gene expression of Arabidopsis thaliana treated with different doses of carbon ion beams irradiation were tested in response to temperature stress,so as to clarify the role of low dose carbon ion beams irradiation in enhancing the stress resistance of Arabidopsis thaliana.The following are the main contents and results of this study:1.Low dose of carbon ion beams irradiation?50 Gy?significantly stimulated the germination index,root length,fresh weight,rosette length and number of seeds per pod of arabidopsis thidopsis seedlings.Carbon ion beams irradiation of 100-200 Gy showed adverse effects.2.The content of hydrogen peroxide?H₂O₂?,the rate of producing superoxide anion(O₂^·-),the activity of hydroxyl radicals?OH^·?and the content of malondialdehyde?MDA?in Arabidopsis thaliana seedlings irradiated by low dose carbon ion beams irradiation?50 Gy?significantly increased compared with the control seedlings.The degree of seed coat etching is related to the dose of carbon ion beams irradiation.In addition,by further analyzing the antioxidant system activity of Arabidopsis thaliana seedlings irradiated at different doses,we found that low dose carbon ion beams irradiation enhanced the activity of peroxidase?POD?,superoxide dismutase?SOD?,catalase?CAT?and increased the content of ascorbic acid?AsA?and reduced glutathione?GSH?.Quantitative analysis of gene transcription expression showed that 50-Gy carbon ion beams irradiation significantly up-regulated the expression of antioxidant related genes.Our results suggested that enhancing the antioxidant system to relieve oxidative stress plays an important role in the stimulation of Arabidopsis growth by low dose carbon ion beams irradiation.3.The transcriptome database of Arabidopsis thaliana seedlings in the irradiated group and the control group was established by RNA-seq,and a total of 228differentially expressed genes were obtained.GO enrichment analysis showed that the genes induced by low dose carbon ion beams irradiation were mainly related to plant cell metabolism,catalytic activity and response to external stimuli.KEGG pathway showed that it was mainly concentrated in plant-pathogen interaction and plant hormone signal transduction metabolic pathway.AP2-EREBP and MYB are key transcription factors in Arabidopsis thaliana seedlings stimulated by carbon ion beams irradiation.4.Under cold stress,50-Gy carbon ion beams irradiation greatly enhanced the growth of Arabidopsis thaliana seedlings compared with the control,while high-dose?100-200 Gy?carbon ion beams irradiation inhibited the growth and development of arabidopsis thaliana.Under low temperature stress,low dose carbon ion beams irradiation significantly decreased ROS and MDA contents in arabidopsis thaliana seedlings,and significantly increased the activity of antioxidant system.50-Gy carbon ion beams irradiation regulated the expression of genes related to low temperature induction in Arabidopsis thaliana seedlings.Our study showed that low dose of carbon ion beams irradiation can improve the tolerance of Arabidopsis seedlings under low temperature.5.Under heat stress,GI,root length and fresh weight of 50-Gy irradiated seedlings were significantly higher than the control,while high-dose irradiation had significant inhibitory effect.ROS and MDA contents in 50-Gy carbon ion beams irradiated seedlings were significantly reduced compared with the control under high temperature stress.Antioxidant system activity was significantly higher than that of the control group.Moreover,the expression of genes related to high temperature stress were regulated by carbon ion beams irradiation.Our study showed that low dose of carbon ion beams irradiation can improve the tolerance of Arabidopsis seedlings under high temperature.In conclusion,low-dose carbon ion beams irradiation can significantly stimulate the growth and development of Arabidopsis thaliana seedlings by enhancing the antioxidant system activity.Plant-pathogen interaction and plant hormone signaling pathways play key roles.Transcription factors AP2-EREBP and MYB play major roles in the stimulation effect of low dose carbon ion beams irradiation.Low dose carbon ion beams irradiation can improve the resistance of Arabidopsis seedlings to temperature stress.