Mechanisms Of The Responses Of ’Micro-Tom’ Tomato To Microgravity Treatment

Microgravity（much less than the gravity of the earth）affects the growth and development of plants,but its physiological and molecular mechanisms,as well as the application value of microgravity in the cultivation of horticultural plants are not fully understood.In this thesis,the 2-D cyclotron is used to simulate the microgravity environment.First,through transcriptomics analysis of the genes differentially expressed in the model plant Arabidopsis thaliana under microgravity treatment,the effect of microgravity treatment on plant gene expression profile is preliminary understood..On this basis,Micro-Tom tomato was selected as the material,and the germination rate of seeds and the fresh weight of the above-ground part of 25-day tomato seedlings,antioxidant enzymes,soluble protein,etc.and tomato fruit related indicators were determined,combined with q RT-PCR technology Analyze the expression level of tomato stress response genes.At the same time,in order to preliminarily find out whether microgravity affects the level of auxin,thereby changing the growth and development of plants,using Arabidopsis auxin response and transporter transgenic lines as materials,the effect of microgravity on root tip auxin levels was analyzed.The research aims to explore the effects of microgravity treatment on the physiology and molecular mechanism of early plant seedlings.The following experimental results were obtained in this research:（1）The wild-type Arabidopsis Columbia（Col-0）was used as the material to perform transcriptomics analysis under microgravity processing.The GO function classification showed that a total of 1018 differential genes were annotated into 42 functional groups in the three GO function classifications.KEGG enrichment analysis showed that 257 up-regulated genes involved a total of 104 pathways.The significantly enriched pathways were mainly pathways such as linoleic acid metabolism and tryptophan metabolism,and 140 down-regulated genes involved 76 pathways.The significantly enriched pathways were mainly For the photosynthesis pathway,etc.These results indicate that microgravity significantly affects the auxin signal and the response process of plant stress and antioxidant stress,thus affecting plant growth and development.（2）Using Arabidopsis auxin-responsive transgenic marker lines DR5:GFP and DR5:GUS as materials,the effect of microgravity on root tip auxin levels was analyzed.The study found that microgravity treatment inhibited the expression of auxin transporter in the root tip,which showed that the GUS staining process became lighter and the green fluorescence intensity of GFP decreased,and the inhibitory effect of microgravity treatment on auxin transporter was observed at 5 days of treatment.The most obvious.Then select the Arabidopsis auxin transporter transgenic lines AUXI:YFP,PIN1:GFP,PIN2:GFP to study the effect of microgravity treatment on the level of auxin transporter in root tip.The study found that microgravity treatment also inhibited the abundance of auxin transport proteins PIN1 and PIN2,which showed that the green fluorescence intensity of GFP fusion protein decreased,while microgravity had no significant effect on the protein abundance of auxin internal flow carrier AUX1.These results indicate that microgravity treatment affects auxin transport and root tip auxin distribution,thus changing plant growth.（3）Microgravity can significantly increase the germination rate of tomato seeds,with obvious promotion effects at 24 h,56 h,72 h and 80 h;microgravity can increase the fresh weight of the seedlings above the ground,and the increase is the largest under the condition of 7 days of treatment.The effect of microgravity on antioxidant enzyme activity in tomato seedlings was further analyzed.The results showed that the SOD activity in the treatment group was significantly higher than that in the control group（P<0.01）,and it gradually increased with the increase of microgravity treatment time.The activity of POD increased first and then decreased.The highest activity was 36.59 μg·g^-1·FW^-1 at 3 days of treatment,which was significantly higher than that of the control group（P<0.01）.The CAT activity showed a trend of increasing first and then decreasing,reaching the highest value of 1790.75 U·g^-1·FW^-1 after 5 days of treatment.In summary,it can be proved that the treatment of tomato seeds by microgravity increases the activity of antioxidant enzymes in seedlings.（4）The results of the analysis of the influence of the physiological and biochemical indexes of tomato seedlings under microgravity treatment showed that the soluble protein content in different treatments showed an increasing trend,and the content in the experimental group treated for 7 days reached the highest value of 0.19 mg · g^-1 · FW^-1,and it was extremely Significantly higher than the control group（P<0.01）.The soluble sugar content increased with the increase of the microgravity treatment time,and the soluble sugar content was significantly higher than that of the control group under 5 and 7 days of treatment（P<0.01）.The malondialdehyde content of tomato seedlings decreased with the increase of treatment time,and it was significantly lower than the control group by 35.1%（P<0.01）under the condition of microgravity treatment for 7 days.Microgravity reduces the SPAD value of tomato leaves.Microgravity treatment increased the total amino acid content in tomato seedlings,especially the proline content.Microgravity environment is a kind of abiotic stress to plants.Therefore,plants adapt to changes in gravity by adjusting related mechanisms to ensure normal growth and development.（5）Microgravity has varying degrees of influence on the expression of five related resistance genes:Sl MCP2 f and SIMAPK6 negatively regulate the expression of plant stress resistance genes,and SIETR6,Sl DEAD31 and ASR1 positively regulate plant stress resistance.The gene of ability showed an upward-regulated trend as a whole.