| Cell wall is the dynamic and complex structure of plant cells and the intermediary of cell interaction with the environment.Under abiotic stress,cell wall structure is remodeled to adapt to new environmental conditions,which is especially important for plant development and adaptation to environmental stress.In this study,the salt tolerant strain Zhong 9807 was used to analyze the changes of cell morphology and metabolites under salt stress.By analyzing the transcriptome of Zhong 9807 under salt stress,two protein genes that regulate cell wall remodeling were excavated: the glycine-rich cell wall component protein gene GhGRP1 and the expansin protein gene GhEXLB1,and we observed the cell wall changes of the cell wall of the cotton strains carrying the two silent genes with the help of scanning electrons and transmission electron microscope.We also studied the expression regulation of the GhGRP1 and GhEXLB1 genes in transgenic Arabidopsis Thaliana and cotton,and the main results are as follows:1.Salt tolerant materials respond to high salt stress by changing the morphology and structure of vascular tissueBy studying membrane permeability and membrane lipid peroxidation of Zhong 9807 under salt stress,we found that Zhong 9807 had higher adaptability to high salt stress than salt sensitive materials.By slicing means to observe vascular tissue morphological in Zhong 9807 under salt stress,it is found that the saltresistant material responds to the external high-salt stress by changing the morphological structure of xylem,phloem and cambium.Through the analysis of the change of leaf weight before and after salt stress,we think that the mechanism of cotton strain response to salt stress is as follows: the vascular tissue first has a stress response related to to plant water holding function,which is manifested as the stress contraction of the vascular bundle area and xylem vessel area in a short period of time,and with the salt stress time,the cotton plant has a recovery process after adapting to this stress.In this process,we found that the content of Dgalactose,D-Galacturonic acid,rhamnosus also increased,showing an increase in pectin content,indicating that pectin was involved in regulation in the process.The increase in the content of Sinapyl alcohol,pCoumaryl alcohol and Coniferyl alcohol indicates lignin was deposited,which indicates that cell wall strength has been increased in response to high salt stress.2.Vascular tissue achieves morphological changes through cell wall remodelingThe results of scanning electron microscope and transmission electron microscope analysis showed that the cell wall extension of cotton strain carrying GHEXLB1 silencing gene was inhibited after salt stress,and the morphological characteristics were cell expansion stagnation,but the effect on cell wall thickening was small,which caused the intercellular layer of three cells to close,and further restricted the expansion and growth of other cells Long.When the cotton strain carrying GhGRP1 gene were subjected to salt stress,the thickening of cell walls in phloem and xylem of vascular zone were inhibited,and the xylem vessels and phloem were compressed in morphology,especially the secondary wall collapse occurred frequently in xylem cells,which indicated that GhGRP1 gene played an important role in the strength of primary wall and the growth and support of secondary wall effect.It was found that the silencing of GhGRP1 gene down regulated the expression of more genes related to cell wall polysaccharide metabolism,and some genes involved in cell wall composition,such as cellulose synthase catalytic subunit CESA3,were significantly down regulated.The silence of the GhGRP1 gene causes the structural support of the cell wall skeleton to be affected,which is the reason why the cell wall becomes fragile.The silence of the GhEXLB1 gene restricts the opening of polysaccharine networks,such as the lignin-degrading gene LAC14 and the XTH6 expression of the glycosaccharine-based hydrolyzed enzyme.The GhEXLB1 gene affects cell wall remodeling more by changing the covalent connection between polysaccharides.3.The expression of GhGRP1 gene was inhibited by high expression of GhEXLB1 geneOur results showed that the endogenous gene ATGRP1 was significantly inhibited in normal growth transgenic Arabidopsis Thaliana compared with wild type.After salt induction,the expression of both genes increased,and the inhibition of GhGRP1 gene by GhEXLB1 gene disappeared.In transgenic cotton,our results are consistent with those in Arabidopsis.GhGRP1 gene and GhEXLB1 gene have opposite effects on cell wall remodeling in the opposite way.The results of bimolecular fluorescence complementation experiments showed that this was a direct inhibition relationship,and this inhibition would disappear with the external stress.4.The expression of GhEXLB1 and GhGRP1 genes is regulated by pectin,which affects cell wall remodelingTranscriptome and metabolomic data analysis showed that some cell wall related polysaccharide metabolites responded to high salt stress in cotton,such as galacturonic acid(HG),and the increase of their contents indicated the increase of pectin content after salt stress.Pectin content and its methyl esterification degree have been proved to be very important for cell wall remodeling in recent studies.In contrast to metabolomics and transcriptomics data,the expression of GAUT1 and PEM6 decreased significantly in gene silenced cotton stain,indicating that the expression of GhGRP1 and GhEXLB1 genes was closely related to pectin,while the expression of pectinesterase gene PEM6 was negatively related to GhGRP1 and positively related to GhEXLB1 gene,indicating that the inhibition of GhGRP1 gene expression by GhEXLB1 gene was regulated by the degree of pectin esterification.Combined with the results of cell wall immunohistochemistry in vascular tissue of transgenic cotton strains,it was proved that pectin affects cell wall remodeling by regulating the expression balance between GhEXLB1 and GhGRP1 genes. |
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