Date of Award

Winter 2008

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biological Sciences

Program/Concentration

Ecological Sciences

Committee Director

Lytton J. Musselman

Committee Member

Rebecca D. Bray

Committee Member

Harold G. Marshall

Abstract

The microspore wall morphogenesis and orbicule ultrastructure of Isoetes were studied using electron microscopy. Microspore wall morphogenesis in five species of Isoetes (I. appalachiana, I. engelmannii, I. hyemalis, I. piedmontana, and an undescribed species from York Co., VA, USA) was studied using scanning and transmission electron microscopy. Results show that they generally have the same developmental stages in terms of microspore wall morphogenesis. The mature microspore wall consisted of four layers: perispore, paraexospore, exospore and endospore. Paraexospore formation began during the tetrad stage. The exospore was then formed between the paraexospore and the plasma membrane. During the free spore stage, two walls were formed, the perispore and the endospore. The perispore develops on the surface of the paraexospore while the endospore was formed interior to the exospore and plasma membrane. Orbicule ultrastructure of nine species of Isoetes from the USA, Canada and Syria was studied, for the first time in the genus, using scanning electron microscopy. Orbicules are minute granules of sporopollenin observed on the inner wall of the secretory tapetum and their function remains unknown. Ultrastructural variation in orbicules of the nine studied species was documented. Orbicules were very variable in both shape and size.

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DOI

10.25777/tddd-rm35

ISBN

9780549936435

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