Establishment And Evaluation Of Mechanical Model For The Regulation Of Roots' Growth In Arabidopsis Thaliana

The influence of mechanical environment on the growth and morphological structure of plant roots has attracted more and more attention from researchers.However,current research focuses on physiological changes in roots under mechanical stimulation,research on quantitative mechanical regulation of roots'growth and development is still lacking.At the same time,the mechanical stimulation of soil's compaction directly affects the development of roots.Different types of soil,such as clay,loam,sandy soil and slab soil,exhibit different rigidity due to the size of medium particles,the force between particles and other factors,eventually it will affect the growth and development of crops and their yield.Therefore,a model with controllable mechanical strength is established to simulate conditions of soil,which is meaningful for studying the penetrated growth of roots in soil.In this project,Agar and Phytagel were selected as two media to analyze mechanical properties,which are often used to cultivate plants.The medium with good linear relationship between concentration and its Young's modulus is selected to establish the experimental model,and the Young's modulus is used to characterize the rigidity.Phenotype of the root,distribution of auxin in root's apex,penetrated growth of Pin1 Arabidopsis thaliana and the expression of ATPase in roots were studied by using the experimental model,whose aim is to evaluate the effect of Young's modulus on roots'growth of Arabidopsis thaliana.This research can provide a new idea for solving the mechanical problem during the growth of plants'roots.Main content and conclusions are as followings:?1?Measurement of mechanical properties about two kinds of media?Agar and Phytagel?and construction of the experimental modelDifferent concentration of Agar or Phytagel and their corresponding Young's modulus were analyzed by the test of uniaxial compression.Experimental model was established by selecting a kind of media with a good linear relationship between the concentration and its corresponding Young's modulus.Results of the experiment about uniaxial compression show:When the concentration is in the range of 0.6%to 1.8%,the relationship between the concentration of Agar and its corresponding Young's modulus is Y=0.0552X-0.0073?R²=0.9448?,and the relationship between the concentration of Phytagel and its corresponding Young's modulus is Y=0.0813X-0.0234?R²=0.9908?.Obviously,the linear relationship between the concentration of Phytagel and its corresponding Young's modulus is more significant?The value of R² is more than 0.99?,which can be used to construct the experimental model.Therefore,according to the linear relationship between the concentration of Phytagel and its corresponding Young's modulus,the required concentration of Phytagel for Young's modulus of 0.03MPa to 0.12 MPa can be calculated,and the experimental model can be finally constructed with the calculated concentration of Phytagel.?2?Exploring the effect of Young's modulus on roots'penetrated growth of Arabidopsis thalianaThe experimental model was used to cultivate Arabidopsis thaliana.When Arabidopsis thaliana grew up to 11 days,the data related to roots'growth were collected and analyzed.For example,the effect of Young's modulus on roots'growth of Arabidopsis thaliana were evaluated by primary roots'average length,curvature of primary roots,number of lateral roots and average length of lateral roots.The results showed that the average length of primary roots in Arabidopsis thaliana was more than25 mm in the range of 0.03 to 0.06 MPa,the curvature of primary roots was kept in the range of 0.88-0.92,the average number of lateral roots was more than 6,and the average length of lateral roots was more than 9 mm and so on.Which means the penetrated growth of primary roots in Arabidopsis thaliana was not affected by the change of mechanical environment.Starting from 0.07 MPa,with Young's modulus increasing,the roots'average penetrated length in Arabidopsis thaliana decreased significantly,curvature of primary roots increased significantly,and the number and average length of lateral roots decreased significantly.Which indicated that roots'growth and development of Arabidopsis thaliana is well when Young's modulus was0.03 to 0.06 MPa.After 0.07 MPa,the roots'growth and development of Arabidopsis thaliana was inhibited obviously with Young's modulus increasing.?3?To explore the effect of Young's modulus on polar transport of auxin in roots'tipsThe expression of apical auxin of 11-day-old DR5-GUS Arabidopsis thaliana cultured in experimental model was analyzed by GUS staining method,and the penetrated growth of primary roots of pin1 mutant which auxin could not be transported normally was also analyzed.GUS staining results showed that expression of apical auxin in DR5-GUS Arabidopsis thaliana was more and more in the range of 0.03 to0.06 MPa.After 0.07 MPa,with Young's modulus increasing,the expression of apical auxin in DR5-GUS Arabidopsis thaliana was less and less.At the same time,when Young's modulus was 0.03 to 0.07 MPa,the ability of penetrated growth in pin1Arabidopsis thaliana,which could not normally transport auxin,was significantly weaker than the wild-type Arabidopsis thaliana.?4?To explore the effect of Young's modulus on expression of ATPase in roots of Arabidopsis thalianaThe expression of ATPase in roots was analyzed by ELISA.The results showed that the expression of ATPase in Arabidopsis roots decreased regularly with the Young's modulus increasing,but this relationship was not linear.Analysis of Origin showed that there is a power function between the Young's modulus of Phytagel and expression of ATPase in Arabidopsis roots,which is Y=0.0051X^-2.775?0.03 MPa?X?0.12 MPa?.Specially,expression of ATPase decreased with Young's modulus increasing,however roots'growth and development were not affected when Young's modulus was 0.03 to0.06 MPa.Which indicated that appropriate amount of ATPase could promote roots'growth and development,and excessive ATPase had no significant effect on roots'growth and development.In conclusion,the experimental model based on Phytagel can significantly regulate the growth and development of Arabidopsis roots,and in a certain range of Young's modulus?0.03-0.12 MPa?,the growth of Arabidopsis roots can be predicted according to the Young's modulus of mechanical environment.At the same time,under the Young's modulus of 0.03 to 0.12 MPa,the roots'growth and development were not strictly inhibited with the Young's modulus increasing,which is contrary to our imagination.When Young's modulus is 0.03 to 0.06 MPa,roots'growth of Arabidopsis thaliana is better,and 0.06 MPa is the most suitable Young's modulus for roots'growth of Arabidopsis thaliana.When Young's modulus is more than 0.06 MPa,roots'growth and development are inhibited with the increase of Young's modulus,and when Young's modulus reaches 0.11 MPa,roots of Arabidopsis thaliana can not penetrate the medium to grow.