| The shape of plant cell has long been the cornerstone of diverse areas of plant research but it is only recently that molecular-genetic and cell-biological tools were been effectively combined for dissecting plant cell morphogenesis.Increased understanding of the polar growth characteristics of model cell types,the availability of many morphological mutants and significant advances in fluorescent-protein-aided live-cell visualization have provided the major impetus for these analyses.The cytoskeleton and its regulators have emerged as essential components of the scaffold involved in fabricating plant cell shape.In this thesis Sagittaria trifolia Lwere used to study the cortical microtubule(CMT) organization and their relationship with cell morphogenesis.The development of aerenchyma in the petiole of S.trifolia was studied by means of light-microscope,scanning electron microscope,transmission electron microscope and immunofluorescence,focusing on the formation of intercellular spaces in diaphragms and its relationship with the organization of CMT arrays.A complex and organized honeycomb-like schizogenous aerenchyma formed by cylinders and vascular diaphragms was observed in the petiole of S.trifolia at different developmental stages.Cell division was the primary factor contributing to the increased volume of air spaces at early stages,while cell enlargement became the primary factor at later stages.The CMTs localized at the sites where intercellular spaces and the secondary cell walls would be formed or deposited during the formation of intercellular spaces by the separation of diaphragm cells.CMTs were observed at the boundary of diaphragm cells and the fringes of intercellular spaces at later developmental stages,where cell expansion occurred rapidly.These observations supported the hypothesis that reorganization of CMT arrays might be related to the formation of air spaces in diaphragms and are involved in the deposition of secondary cell walls.The vascular bundles appeared in diaphragm of the aerenchyma in petioles of S. trifolia being classified to primeray and secondary vascular bundle.All vascular bundles were come of diaphragm cells by changing their shapes.In this process,the diaphragm cells differentiated into tracheary elements with the CMTs reorganization. This result suggested that the diaphragm cells and the tracheary elements might share similar developmental characteristics.Essential mineral elements like Potassium(K),Mg,Cu,Zn,Ca and P in the cell wall of aerenchyma cells in petioles of S.trifolia at five different developmental stages were analysed by CSEM-EDX.At early stage,K and Cl concentrations in cell wall were high up to 36%and 4.3%of dry weight,respectively.It supported the hypotheses that aerenchyma spaces were filled with liquid at early developmental stages of aerenchyma in S.trifolia petiole.Magnesium concentration was high at stage 2,up to 0.86%of dry weight.Zinc and Cu were detected only at rapid expansion stages,during which the concentrations were up to 1.5 and 2.5%, respectively.Calcium was detected in the cell wall only at mature stages,the concentration was high up to 1.3%of dry weight at stage 5.These results confirmed that the element concentration of aerenchyma cell wall undergwent dynamic changes during the different developmental stages,and a low Ca with high Zn and Cu concentration were needed for cell expansion.Cu and Zn deposition in the cell wall showed a significant positive linear correlation,suggesting that these two elements shared same or similar uptake and transport mechanism in plants.Three plasmids,named pTUA-6-GFP,pGFP-TUA6 and pMAP65-6-GFP were constructed and transferred into in Arabidopsis.The expression of these fusion genes in Arabidopsis will further be analysed and used to analyze the function of CMT or/and MAP65-6 with fluorescent protein aided live-cell visualizations.
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