Functions Of Polar Auxin Transport In Root Mechanoresponses In Arabidopsis

Plant root system is essential for acquisition of growth-and development-sustainingwater and nutrients from soil environment. Mechanical stimulations, including physicalimpedance, later pressure and frictions by soil particles, are experienced by root systemthroughout development, and can substantially influence root system architecture.However, it is still unclear how plant roots sense mechanical stimulations in soilenvironment and response appropriately in order to establish adaptive growth in localsoil environment[1]. Beside root system, mechanically-induced plastic growth anddevelopment also occur in plant green tissue. It is proposed that similar cellular andmolecular mechanisms may be employed by different parts of plant seedlings inmechano-transduction and–response[2-3]. Therefore, investigation of plant root systemmechano-response and the underlying physiological mechanisms is fundamental fordevelopment of plant mechanobiology and important for application of mechanicalstimulation in agricultural practice.Plants use endogenous signal transduction systems to percept and transmit externalenvironmental stimulations, and employ hormone crosstalk and gene expressionnetwork regulation to integrate environmental stimulations with endogenousdevelopmental cues. The versatile phytohormone auxin controls a wild range plantdevelopment progresses through its polar transport and local concentration gradientformation. Modern plant mechano-response researches mainly focused on the influenceof mechanical stimulations on plant growth, development, morphogenesis and aspectsof physiological and biochemical processes. The correlation between auxin polartransport and mechanisms of plant mechano-response has mainly not been explored.Here, I examined the contribution of contribution of auxin polar transport inmechanically induced root system growth and development in Arabidopsis thaliana.During this research, multidisciplinary principles and methods betweenphytophysiology and biophysics were used, such as performing of continuousmechanical stimulation on growing roots and supplementation of specific auxin polartransport inhibitors in growth media.The first part of this research was to build the method of mechanical stimulation.The impenetrable agar with different concentration (ranging from8g/L to22g/L) wasused to cultivate the Arabidopsis thaliana tipsily. The hardness and surface roughness of agar were optimized by the estimation of the increment and ratio of curvature of rootsfor the subsequent experiments. The results indicated that the increment of taproot,lateral root density and length were suitable for the follow-up experience when theconcentration of agar was10g/L and12g/L. The second part of this study was to studythe phenotype of Arabidopsis thaliana root under different mechanical stimulations. TheArabidopsis thaliana was cultivated tipsily with the agar concentration of10g/L and12g/L, and the skewing angles were30°,45°,60°and75°. The optimal skewing angle wasfound by determination of the increment and ratio of curvature of roots, number anddensity of lateral root, an appropriate increment of taproots and obvious waving wouldbe the criterion for the choice of concentration of agar and skewing angle. The third partof this study was to investigate the effect of inhibitor on the phenotype of Arabidopsisthaliana roots under mechanical stimulation. Different concentration of Polar transportinhibitors (NPA and1-NOA) ranging from0.5μM to2.0μM were used in this study.The results indicated that there was no obvious inhibition for the Arabidopsis thalianataproots when the concentration of NPA was0.5μM by determination of the path lengthand straight line of taproots. However, when the concentration reached up to1.0μM,the path length and straight line of taproots were inhibited synchronously. While thepolar transport inhibitor1-NOA also displayed an inhibition phenomenon for the growthof Arabidopsis thaliana roots, the number of lateral roots decreased with the increase ofconcentration of1-NOA. But there was no obvious inhibition for the growth of taproots.And the waving of roots was observed in all experiment groups.Overall, the results from this study indicated that the concentration of agar andskewing angle influenced the growth of taproots and lateral roots of Arabidopsisthaliana. The increase of concentration of agar would increase the hardness of culturemedium, and then change the surface roughness and decrease the length of taprootsobviously, which demonstrated that different intensity of persistent mechanicalstimulation has a significant impact on the growth and development of Arabidopsisthaliana roots. In addition, minute quantity of NPA (0.5μM) could remedy thedeformation of taproots causing by the mechanical stimulation. And the inhibition forthe taproots was obvious when the NPA concentration increased to1.0μM, which alsodisplayed a strong inhibition effect on the growth of lateral roots.1-NOA didn’t displayan evident inhibition effect on the taproots, but the sensitive to mechanical stimulationwas enhanced. A bigger waving was observed in the experiment, and1-NOA has aninhibition effect on the lateral roots. The experiments indicated that there was a different inhibition effect between different polar transport inhibitors and concentrations, and thedifferent concentration of auxin in the cell’s internal and external environment have asignificant effect on the morphogenesis, growth and development of plant roots undermechanical stimulation.