| The development of endodermis in plant roots generally goes through two stages: the first stage is the formation of lignin deposition,which can block the apoplastic pathway,and that is the formation stage of casparian strip;the second stage is the formation of suberin lamellae,which can block the coupled trans-cellular pathway,and that is the thickening stage of casparian strip.The formation and thickening of the casparian strip in the endodermis result in that the external water and solute can only enter the stele through the symplastic pathway,which guarantees the selection ability of plants when they transport materials from the outside to the inside.Through the application of PEG and ABA on 84 K poplar(Populus alba ×P.glandulosa cv`84k’),the purpose of this study is to identify that what would happen to the thickening of casparian strip if ABA signals was applied to the plant and PEG was used to simulate the drought stress.The main findings are as follows:1.The formula of 84 K poplar asexually expanded MS(Murashige & Skoog)rooting medium and common MS medium was determined through a comparative experiment.It was found that certain amounts of auxin naphthaleneacetic acid(NAA),indolebutyric acid(IBA),and Plant tissue culture antibacterial agent(PPM)can promote the growth of plant stem segments.However,in the process of simulating drought stress,continued cultivation of plants with auxin-containing medium will offset the effects of drought stress on plants which will interfere with the results of experiment.Therefore,an experimental method for transplanting from the rooting medium to the stress medium was confirmed.2.It was found that the use of PEG to simulate the drought stress and the application of ABA signals to plants can cause retardation and even death of the external morphology of 84 K poplars,and also promote the thickening of casparian strip in the roots of 84 K poplars.In addition,the thickening of casparian strip changes when the intensity of the stress and the duration of the stress change,which indicates that the ABA signal is involved in the formation of suberin lamellae.3.Using polyubiquitin protein(UBQ)as an internal reference gene,17 genes associated with casparian strip of the 84 K poplar root c DNA were selected for real-time fluorescence quantification detection.The results showed that the 17 genes could be divided into three types,About type 1,there was no significant difference in the effect on gene expression when PEG and ABA treatment,like MYB41,it may be a regulatory factor for suberin thickened when the second stage of casparian strip and involve in the development of casparian strip under drought stress and ABA treatment.About type 2,PEG treatment had a higher gene expression than ABA treatment,like ABCG2,ABCG20,ABI3,ABI4,CASP1,CASP2,CYP86B1,ESB1,MYB36,PYL,SNRK2.2 and SNRK2.6,it is mainly involved in the regulation of the development of casparian strip under drought stress.About type 3,PEG treatment had a lower gene expression than ABA treatment,like ABCG6,CASP3,GASSH01 and GPAT5,this type of genes may be mainly involved in the regulation of the development of the casparian strip under ABA treatment.Our results also showed that PEG drought stress and ABA treatment induced different effects of gene expression,means the regulatory mechanism of enhanced development of the casparian strip under PEG drought stress and ABA treatment may not be identical.This study show that the PEG and ABA drought stress can promote the casparian strip ticken at the root of poplar,show the plant response to drought stress,also introduce the ABA signal to the control network of the cortex casparian strip development of trees,it lays a foundation for further research on the development of trees roots and their response to the environment. |
