Effects Of Naphthalene Acetic Acid On The Growth And Development Of Arabidopsis Thaliana

Arabidopsis is a model plant belonging to the dicotyledonous plant whose roots are composed of the main roots,lateral roots and adventitious roots,and their effects on the environment and plant hormones are different.For example,high concentrations of auxin can promote the initiation and formation of lateral roots(LR),while inhibiting the growth of the main root(PR).The main root tip of Arabidopsis thaliana can be divided into the area of meristem,elongation,mature area,root and other areas,the division of the cell division ability,elongation is the fastest root extension of the place.Auxin is involved in regulating the growth and development of the main root and lateral root,and has the function of regulating the division,elongation and differentiation of the cells.In order to explore the mechanism of auxin on the development and formation of root and lateral roots of Arabidopsis thaliana,0.0125,0.025,0.05 and 0.1 mg/L four concentrations of auxin analogue naphthalene acetic acid(NAA)were used to treat Arabidopsis thaliana.The change of the root length and the number of lateral roots in Arabidopsis thaliana under different treatments,and explain the mechanism of this change from the aspects of cell biology and molecular biology,respectively,with the change of main root length and number of lateral roots.1?Exogenous NAA treatment inhibited the elongation of the main root,and the higher the concentration,the more obvious the inhibitory effect.In this paper,the changes of the meristem,elongation and mature area were observed by microscope.The length of the area was longer and the length of the extension zone was shorter and the length of the mature area was basically unchanged.It is shown that NAA inhibits the elongation of the main root,mainly suppressing the length of the elongated region.The number of cells and the number of cells in the elongated region were measured for three consecutive days.The cell length was longer and the number of cells was not changed,indicating that NAA promoted cell length expansion in the elongated region without affecting its ability to divide That is,NAA by inhibiting the elongation of the cell length expansion,thereby reducing the length of the elongated area,thereby inhibiting the elongation of the main root.Auxin achieves cell elongation by relaxing cell walls and increasing cell wall compression,and this function is achieved by auxin binding protein ABP1.The level of intracellular ABP1 gene is closely related to cell elongation.The results of real-time quantitative PCR showed that NAA inhibited the activity of ABP1,thus inhibiting the elongation of elongated cells.The auxin input vector AUX1 and auxin effluent vector PIN1 were related to the maintenance of cell growth hormone concentration gradient The effect of NAA on lipophilicity is through the diffusion of NAA into the cells,so the relative expression of AUX1 does not change,while the high concentration of NAA degrades the expression of PIN1 protein in the root,thus inhibiting the polar transport of auxin,and thus Inhibit the elongation of the main root.2 ? The treatment of exogenous NAA can increase the number of lateral root primordia and the number of lateral roots,and the higher the concentration,the stronger the promoting effect.The lateral roots of Arabidopsis thaliana begin with the middle column sheath cells facing the native xylem,and the high concentration of auxin can stimulate the division of the column sheath cells,resulting in a large number of lateral roots.And the process of lateral root formation is divided into four stages.Each stage is regulated by different genes,and exogenous NAA can promote the formation of lateral roots by changing the relative expression of genes in the control lateral root.The first stage of the auxin signal transduction process: auxin signaling molecules through the auxin inbound transport carrier AUX1 transported to the middle column sheath cells,and then through the plasma membrane of the auxin transport carrier carrier protein transport to the extracellular,thus In the root to form a growth hormone concentration gradient,which is the necessary conditions for the formation of lateral roots;and the level of PIN protein content and by the regulation of P5PIK2 gene.After treatment with exogenous NAA,the expression level of P5PIK2 gene in roots increased,and it was more favorable to complete the molecular conductance process of auxin signal to form concentration gradient.In the second stage,the initiation process of the lateral root primordia: the auxin in the middle column sheath cells after the formation of different concentration gradient,the direct binding and activation of transport inhibitor response protein TIR1 led to AUX / IAA protein IAA14,IAA28 by ubiquitin-protease Degradation of the body degradation pathway.The degradation of IAA14 in the roots allows the auxin response factors ARF7,ARF19 to be activated,and then activate the transcription of the downstream genes LBD16 and LBD29 genes regulated by it,thereby activating cell proliferation and morphological transcription.While the decrease of IAA28 content,the release of the auxin-induced lateral root-forming gene transcription inhibition,Which is conducive to the formation of lateral roots.The third stage is the lateral root primordium differentiation process: exogenous NAA treatment,the increase of nuclear protein ALF4,promote the division and differentiation of the middle column sheath cells;And the increase of ACR4,which inhibits the division and differentiation of other adjacent non-lateral root cells.The fourth stage is the lateral root breakthrough epidermis process: exogenous NAA treatment,the growth of auxin input carrier LAX3 content increased,promote the cell wall decomposition enzyme content increased,and thus conducive to cell wall decomposition and cell separation,making The lateral roots of the base layer can break through the peripheral cells,exposing the surface,outward growth and development.This paper deepens the understanding of the signal pathway and molecular mechanism of exogenous NAA on the root development of Arabidopsis thaliana.These studies provide some reference value for the further study of the mechanism of exogenous auxin affecting plant root development.