Date of Award
Doctor of Philosophy
The plant cell wall is a vitally important interface connecting plant cells to their outside environment and neighboring cells. Acting as a hub for defense, signaling, and physiological processes, the plant cell wall was a crucial innovation in plant evolution. Current cell wall models are largely based on what has been observed in plants like Arabidopsis, Pisum sativum, Nicotiana tabacum, and Phaseolus vulgaris. These models are unable to consider the variety of polymers in a given wall, the mechanical and functional properties such polymers impart, and the complexity of interactions among polymeric cell wall constituents. This work deepened the understanding of wall composition of specialized walls that fall outside of the scope of current plant cell wall models. A detailed survey of cell wall polymer distribution in the transfer cell walls in three key bryophyte species the model moss Physcomitrium patens, hornwort Phaeoceros carolinianus, and liverwort Marchantia polymorpha was done utilizing histochemical techniques in the light and florescent microscopes coupled with immunocytochemical localization with monoclonal antibodies (MAbs) in the transmission electron microscope (TEM). This work demonstrated that the occurrence, abundance, and types of polymers differ among taxa and between the two generations, are more influenced by developmental and life history needs than the similar function of the cells in individual taxa. A notable difference between generations was seen in M. polymorpha with the LM2 and JIM13 MAbs targeting AGP epitopes. However, findings in P patens appear to lack the differential labeling observed in both M. polymorpha and P. carolinianus. Using these same techniques, the walls and matrices involved in the process of spermatogenesis were examined in the moss P. patens and noted differences in abundance and location of cell wall polymers during sperm cell differentiation. Another notable finding of this work was that high concentrations of arabinose as components of AGP and pectins are important in the walls of P. patens during the process of spermatogenesis. The final study focused on utilizing herbarium specimens to explore the application of immunogold localization on dried collections of the moss Polytrichum up to 100 years old. The studies compiled in this dissertation demonstrate that the major cell wall components, cellulose, pectins, hemicelluloses, and callose, are constituents of special walls in three bryophytes, but they are differentially expressed within cell types and across these plants. Taken together, these works contribute significant new data on the composition of plant cell walls by focusing on bryophytes and the unique cell walls vital to the life history processes of spermatogenesis and placental function. These findings also show that both field-collected and herbarium samples are successfully labeled with MAbs at the TEM level, unlocking the potential for further studies across time and taxa using plant collections.
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