Modeling And Experimental Study On Force Regulating The Growth Process Of Cells And Root Organs In Arabidopsis Thaliana

The plant growth and develoment not noly rely on the complex network of genetic regulations but also can be interpreted by the the physical environment.The interdisciplinary researches in microenvironment regulating plant growth and development field have fascinated associating biologists and physicists for many years.Motion in plants is driven by the variation of water content within the tissue to achieve anisotropic swelling and shrinkage.Some species use mechanical instabilities,to speed up their movements,such as fracture,buckling,and snapping.At the molecular level,the four original Arabidopsis TCH genes have been demonstrated that the expression of a vast collection of Arabidopsis genes can be significantly influenced by mechanostimuli.However,the important basic problems like “Does the internal law of the force microenvironment is existed in plant growth and development?” and “How do stresses adjust and control plant growth and development quantificationally?”,have lagged our understanding from plant biomechanics perspective.This paper researches two scales of cell and organ in the Arabidopsis thaliana.The models which base on the Eshelby equivalent inclusion approach,Kirchhoff's dynamic analogy theory and Lyapunov theory on stability of the motion,is established to analyze varying pattern of plant growth behavior.The models was demonstrated by the validation experimentation.This study enriches theoretical basis of vegetable physiology and development,also provides a new approach for the application of mechanobiology.Following are the main studies of the present thesis:At the cell scale,a protoplast can be treated as a inclusion in the agar gel.The cell shapes change is occurred while turgor presssure altered.On account of Eshelby equivalent inclusion theroy,the mechanical response of plant cells in the turgor pressure change process can be evaluated by the eigenstrain.In this paper,a composite model of the Arabidopsis thaliana single cell embedding in the agar gel can predict the change of rigidity of plant cell,and the influence of living cells growth behaviors.The variation of cellular bulk modulus and shear modulus can be adjusted by the volume fraction of the composite system and the mediumPoisson's ratio.In short,with the external mechanical stimuli,the comprehensive system is always keeping decrease trend of free energy.At the organ scale,the Arabidopsis thaliana primary root is treated as an isotropic cantilever beam with equal cross section.Based on Euler-Bernoulli beam theory,their kinematics and deform can be discussed without shear deformation.This dissertation presents a formula for the large deflection deformation between the primary root and the culture medium,as well the model can speculate the root tip motion trail under the terminal load(force load and bending load).While the number of elliptic integral inflection points increases,the model shows that the force and bending on the root tip enlarge.Experimental observations have shown that,when primary roots are cultured on tilted agar surfaces,their skewing growth and waving growth phenotypes are significant impacted by the skewing angle and density of agar medium.The skewing and waving phenotype while Arabidopsis thaliana root growth in the agar medium,is interpreted as a combination of mechanical buckling induced by circumnutation and thigmomorphogenesis.Arabidopsis primary root is assumed to have an isotropic circular cross-section of equivalent radius.By using Euler angles to describ the rod tip kinestate,based on Kirchhoff dynamic analogy method,the elastic rod is transformed to discrete systems.Moreover,the equilibrium issue can be discussed by Lyapunov stability theory of discrete dynamic systems.To model the stability of primary root under the axial stress,we used a nonlinear theory describing the Arabidopsis root organs morphology modulated by continuous mechanical disturbance as observed in our experiment.This investigation has translated cell shape changes and root organ kinematics into a quantified mechanical and geometrical output.By discussing the contribution of mechanical forces in plant growth,it can provid theoretical support for screening of germplasm resources in controlled environment,expanding the study of agricultural resources utilization efficiency.