Quantitative Study Of Mechanical Stimulation And Exogenous ATP On The Regulation Of Arabidopsis Root Growth

Roots are the most important nutrient-absorbing organs of plants.Previous botanists have done a lot of research on the regulation of root growth by mechanical stimulation.These studies focus on physiological and biochemical reactions and regulatory mechanisms within plants,but are there quantitative relationships between mechanical stimulation and plant root growth?This question has not been answered very well.In order to study the quantitative relationship between force and plant root growth,Arabidopsis thaliana was used as a model to study the growth length,horizontal growth index,straightness and 7 proteins of Arabidopsis thaliana that respond to mechanical stimulation.We design experimental models of plant roots grow in two quantitative mechanical environments by adjusting the tilt angle of the medium and changing the concentration of agar in the medium and study the intrinsic relationship among the controllable mechanical environment stimulation and the root growth,auxin transport and ATP release of Arabidopsis thaliana.The quantitative relationship between mechanical stimulation and ATP affecting plant root growth was explored from the organ,tissue,and protein levels.This topic is conducive to the promotion of quantitative biological research on plant root growth,deepen the theoretical understanding of plant growth and development,and has practical significance for guiding agricultural production.The main contents and results of this paper are as follows:(1)In order to establish an experimental model in which the Arabidopsis roots were subjected to a gradient controllability of 0-0.8 G in the direction of the vertical agar surface,we adjusted the tilt angle of the medium:0°-53°,in this experimental model of controlled mechanical environment.Quantitative study of Arabidopsis root growth length,main root skew and wave growth,ATP and auxin-related protein expression.After statistical analysis,we find that with the increase of mechanical stimulation:a).the length of the main root increased at 0 G-0.4 G,reached the maximum length at 0.4 G,increased by 18.36%,and gradually decreased at 0.4 G-0.8 G;b).The HGI value increases linearly,and the HGI value increases by 38.5%at 0.8 G;c).The straightness value decreases linearly:y=-0.0496x+0.9433,where y is the straightness value and x is the external force(G).R~2=0.979,the straightness decreased by 9.4%at 0.8 G;d).The distribution of auxin in root tissues changed,apical auxin accumulation;e).The expression of AtAPY,AtPGP and AtPIN closely related to ATP and auxin.There was a significant difference,in which AtPIN1/AtPIN2 increased linearly,AtAPY1/AtAPY2At/PGP4 protein expression increased,and AtPGP1/AtPGP19expression decreased.Quantitative analysis of protein expression showed that these proteins had obvious responses to mechanical environment changes.This part of the experiment verified the changes in the induction mechanical environment of Arabidopsis thaliana grown on the surface of inclined medium,regulated root growth,changed the concentration of ATP and auxin in the cells,and there was a quantitative relationship between them.(2)The agar concentration in the medium was adjusted in the range of 0.6%-2.4%(w/v),and the experimental model of the surface mechanical environment of the culture medium was designed.The surface structure of the medium was observe by uniaxial compression,uniaxial stretching and scanning electron microscopy.We calculate the medium breaking load and elastic modulus.The breaking load and elastic modulus increased linearly in the medium at 0.6%-2.4%agar concentration.Scanning electron microscopy showed that the surface roughness of the medium increased with the increase of agar concentration,and the resistance of Arabidopsis roots will rise,indicating a mechanical environment with a gradient difference between the culture media at this concentration.In this model,the intrinsic relationship between culture medium differences and Arabidopsis root growth and ATP and auxin-related protein expression was investigated.With the increase of agar concentration:a).the main root showed a decreasing trend,at 2.4%concentration,the length of the main root decreased by 25.17%;b).the length and density of root hair increased;the HGI value increased by the trend of the quadratic function curve,in agar.At a concentration of 2.4%,the HGI value increased by 60.5%;c).The Straightness decreased linearly:y=-3.09x+0.9731,R~2=0.9778,where y is the Straightness value,x is the agar concentration(w/v).At agar concentration of 2.4%,the Straightness value decreased by 9.9%;d).After curve fitting,the relationship between AtAPY,AtPGP,AtPIN expression and agar concentration is a power function.These results indicate that a controlled mechanical environment plays an important role in the regulation of Arabidopsis growth and that there is a quantitative relationship between them.(3)In the third part of this paper,we designed an experimental model of gradient exogenous ATP(0-3 mM ATP)culture conditions to explore the quantitative relationship between ATP and plant root growth,with the increase of exogenous ATP concentration:a).The length of Arabidopsis root decreased linearly,the HGI value increased linearly,the straightness value decreased linearly,b).The auxin accumulation gradually increased;c).The APY protein expression increased linearly which is the most directly related to ATP decomposition,and the relative expression of exogenous ATP concentration(x)and AtAPY1(y)In accordance with the equation:y=1.1606x+1.159,R~2=0.9769,the relative expression of exogenous ATP concentration(x)and AtAPY2(y)accords with the equation:y=1.2046x+0.8505,R2=0.9782.In addition,the expression of PGP protein decreased linearly,and the trend of the PIN protein expression quadratic function curve increased.These results demonstrate that the exogenous ATP inhibits the growth-promoting of of Arabidopsis root skew,and this process is directly related to the transport of auxin.The conclusion also indicates that there is a direct relationship between ATP and plant-induced external mechanical environment changes.In summary,we obtain similar growth phenotypes and the protein expression trends of Arabidopsis thaliana in two mechanical environments,which are affected by external forces to alter the growth morphology of Arabidopsis roots.This is due to the changes of auxin sexually transported and the tissue distributed by the release of ATP from root cells.A similar root phenotype appear under the treatment of exogenous ATP.Protein expression analysis further prove the relationship between the mechanical stimulation and ATP.The intrinsic relationship between mechanical stimulation and the plants growth is inversely studied through the third part of experiments,and the theoretical system is enriched.The conclusions of this paper can further improve the theory of mechanical environment affecting plant growth,and we have obtained the quantitative relationship between Arabidopsis root growth and the single mechanical environment,which provides experimental reference for future quantitative biology research in this aspect.