Cytological Observation And Composition Analysis Of Casparian Strips In The Endodermis Of 84K Poplar

Casparian strip is the specialized structure of the inner cortex in the primary structure of plant roots.In dicotyledonous plants,Casparian strips generally exhibit as the ring bands,lignified and corked structures formed on lateral and radial walls,while in monocots they appear thickened on five sides.Casparian strips are able to selectively control oxygen,water,ions and nutrients,etc.,entering the middle column through plant roots,so they play a vital role in regulating plant absorption and nutrient acquisition.Recent years,studies on the physiological function of plant endothelial Casparian strips have obtained preliminary results.However,in woody plants,the structure and chemical composition of Casparian strips at different developmental stages and their distribution in the endothelial layer still need to be further elucidated.In this research,cytological observation and component analysis of Casparian strips of primary roots in 84 K poplar(Populus alba ×Populus glandulosa)were performed.By comparing the components of Casparian strips and the expression levels of related genes in different developmental stages,the cytological structure,chemical composition of Casparian strips in the different development processes were clarified.(1)The staining observation based on lignin dye resorcinol showed that the distribution of lignin in the endodermis close to the vascular tissue was significantly higher than that in the surrounding cells,and the number of endodermal cells showed an upward trend with the development and maturation.(2)Using laser scanning confocal microscope technique to observe and analyze the cross section of the primary root of 84 K poplar at different developmental stages,we found that the endodermal cells morphology containing Casparian strips were obviously different from the surrounding cells,and the radial cell wall showed obviously band thickened.(3)The staining observation based on suberin dye FY-088 found that the deposition of Casparian strips suberin gradually thickened with the development and maturation of the staining.(4)By using Stimulated Raman scattering microscopy,label-free imaging with in situ analysis of endodermal cells at different developmental periods were carried out.It is further proved that the main components of Casparian strips are lignin and suberin,as well as the content of lignin and suberin increases with the development and maturity of the endodermal cells,and the distribution of lignin and suberin increased gradually from dot deposition to uniform distribution.(5)By means of Fourier transform infrared spectroscopy technique,the Casparian strips infrared spectra of different developmental stages isolated by enzymatic hydrolysis were analyzed.Both the young and the mature regions have obvious characteristic absorption peaks of lignin and suberin,and the absorption peaks of the two contents in the mature regions are significantly higher than those in the young ones,supporting the hypothesis that the content of lignin and suberin in the mature regions is on the high side.(6)Moreover,quantitative real time PCR further revealed that the expression of genes related to the development and synthesis of the mature regions Casparian strips of 84 K poplar in primary root were all higher than that of the young ones.Taken together,the endodermal cells containing Casparian strips in the primary root of 84 K poplar is obviously different from the surrounding cells,and the number of the cells increases significantly with the development and maturation.The composition of the Casparian strips mainly contains lignin and suberin,both almost simultaneously deposited.In addition,as the seedling matures,lignin and suberin gradually deposited along the endodermis,and the content of both increases significantly.These results provide a theoretical basis for elucidating the developmental characteristics and physiological functions of the Casparian strips of woody plants.