Graduate Thesis Or Dissertation
 

Ultrastructure of parenchyma and sclereids in Douglas-fir [Pseudotsuga menziesii(Mirb.)Franco] bark

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/sn00b134v

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  • Because Douglas-fir [Pseudotsuga menziesii(Mirb.)Franco] bark is a raw material produced in our renewable forests along with wood, an understanding of the ultrastructure of bark cells is of paramount importance if wood technologists are to utilize the bark to the fullest potential. The objectives of this study were to develop microscopic techniques in order to 1) describe and illustrate ultrastructurally the anatomy of parenchyma cells present in phloem and changes that occur to them in rhytidome formation, 2) describe and illustrate pitting between sclereids and adjacent cells. To accomplish these objectives required the development of procedures. Standard techniques were used, modified and integrated with newly developed techniques. Micromanipulation of cells and tissues was required. Stereo, light, phase contrast, fluorescence, scanning electron and transmission electron microscopy were employed. The developed procedures resulted in successful bark preparations for ultrastructural examination. The results of this study showed that the longitudinal phloem parenchyma are connected by thin pit areas similar to primary pit fields and not by well defined simple pits as found between parenchyma cells in the xylem. The cell wall of the longitudinal parenchyma is a layered structure with orientated microfibrils. Expansion of the phloem parenchyma with rhytidome formation involves a stretching out of wrinkled and folded cell walls to fully expanded and smooth cell walls. Pitting between a sclereid and a parenchyma cell consists of a long pit canal through the sclereid wall about one micrometer wide with little or no flaring out at the outer surface to form a pit chamber. The pit membrane is the original double cell wall of the parenchyma. Pitting between two sclereids exhibited similar long pit canals extending across the sclereids into a chamber area separated again by a thick pit membrane consisting of the original double cell wall of the parenchyma. Additional layers of secondary wall apparently are deposited by apposition on the original parenchyma cell wall in the pitted region during sclereid formation.
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