| Summary: | 博士 === 國立臺灣大學 === 分子與細胞生物學研究所 === 93 === This study first proposed a new method for leaf age, the Leaf Measuring-Interval Index (LMI), to replace the Leaf Plastochron Index (LPI) method that often used in the leaf morphological and physiological studies. The LMI method is not dependent on plastochron and it is based on using a constant measuring interval (Mi) to record the leaf growth information. LMI of the leaves is obtained by transferring their growth data with formula, which is obtained according the reference leaf length λ. This method can solve the problem of using LPI when leaf plastochrons are variable especially when plants growing in stress environments. The LMI method depends on three assumptions. First, the early stage of leaf growth is exponential. Second, the exponential rates of successive leaves are the same. Final, the chose of Mi is less then the period of exponential growth of leaf.
Morphological and ultrastructural features of hydathodes in Ficus formosana Maxim. f. Shimadai Hayata were studied in the second part of this dissertation. The laminar-hydathode is complex epithemal type, which consists of water pores and epidermis, tracheid-ends, epithem cells, and a sheath layer. Water pores are made up with two similar guard cells and the pore between them opens permanently. The epithem is consisted of a group of parenchyma cells with sinuous cell wall. On the ultrastructures, the epithem cell has a dense cytoplasm, numerous mitochondria, an extended ER, ER-derivative vesicles, many small vesicles derived from Golgi bodies, and proliferate peroxisomes. The numbers of peroxisomes were increased and coincided with the maturity of the epithem. In addition, abundant plasmodesmata were often observed on contacted cell wall between epithem cells. Multiple types of plasmalemmasome structures were also presented on the plasma membranes of the epithem that are results of endocytosis, which are performed during repeat cycles of plasmolysis and deplasmolysis. Hydathode is an idea system for studying endocytosis in plants was suggested.
Ultrastructural studies on the salt injury of guttation on hydathodes show that the major symptoms of salt injury are as follows: many electron dense particles spread in the nucleus and organelles; the nucleolus is condensed and then disappeared, and the endomembrane system is collapsed then entirely formatted osmiphillic materials in the cytoplasm. Upon dehydration, the collapsed membranes become the myelin-like structures. According different degrees of salt injury on epithem, the abilities of different tissues’ salt-tolerance are variable and the salt tolerance of epithem is better than other tissues. It means that some special mechanisms in the epithem have been evolved to adapt high salt stress. In addition to physiological metabolism regulation, there are two suggestions that the sinuous cell wall increases the absorption surface of epithem with environment and that the abundant endomembrane system not only accelerates the cells’ response to salt stress, but also increases their salt-tolerance via fluid-phase endocytosis. These mechanisms may promote the tolerant efficiency of vacuoles in epithem cells under high salt stress.
The morphogenesis of hydathodes in chapter three, the identified the processes of development into four stages: I, initial stage; II, cell division stage; III, cell elongation and cell differentiation stage; and IV, maturation stage. In the early stage of leaf development, the initial cells of hydathodeoccur near the region of a giant trichome cell base. Afterward in the cell division stage, epidermal initial cells are proceeding anticlinal division to form epidermal cells and water pores in the further, and subepidermal initial cells through anti- and periclinial divisions to produce a group of cells, which will be differentiated into epithem, tracheid and a sheath layer of hydathodes. During the cell elongation and differentiation stages, epithem cells grow becoming lobed shapes that are caused by some factors, which contain the special microtubules arrangement around the pericytoplasm, digesting enzymes secreted to cell wall acting, and the tension force causing by turgor of cell growth. These factors are not only causing the lobed cell formation, but also enlarging the intercellular spaces of epithem. The lobed shape’s epithem cells increase the contact surfaces between the cells and their environment. At the same time, tracheids are also starting differentiation and increasing rates in the numbers of water pores are reaching maximal on epidermis. In the maturation stage, tracheids within epithem are gradually matured, and associated with maturation of epithem cells and water pores, functioning as the passage between vein-ends and water process guttation. It is interesting that the way of epithem differentiation and maturation is starting from the regions under water pores to vein-end region. Since the epithem near the vein-ends are maturation, the guttation will be apparently.
Finally, the lanthanum nitrate was used as an apoplastic tracer to study the retrieval mechanisms of epithem. Cytochemical data indicated that the epithem cell might also use the coated-vesicles endocytosis to retrieval nutrient from the guttated solution in addition to use proton pump.
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