UBC Theses and Dissertations
Mapping xylan biosynthesis in plant Golgi and teaching biology using example answers Meents, Miranda J.
Secondary cell walls (SCWs) containing the hemicellulose xylan are essential for normal plant growth and development. Great strides have been made to identify the many Golgi-localized biosynthetic enzymes that work in concert to make xylan, however, we still understand little about how these critical proteins and their product are organized in the Golgi to facilitate synthesis and trafficking. To address this question, I characterized the Arabidopsis Golgi in cells producing SCWs using a combination of confocal and transmission electron microscopy (TEM). This analysis indicates that the number of Golgi stacks increases significantly with the onset of SCW synthesis, and that during this process the randomly distributed Golgi stacks work together to produce and secrete xylan. Furthermore, nanoscale characterization of Golgi structure revealed significant increases in Golgi diameter, swelling of the cisternal margins, and secretory vesicle size. Loss of the xylan-biosynthetic enzyme IRREGULAR XYLEM 9 (IRX9) resulted in a dramatic increase in cisternal fenestration and a decrease in swollen margins, but did not affect the number or size of Golgi. Finally, immunogold labelling was used to map IRX9-GFP and xylan to different regions of Golgi cisternae, indicating that xylan is abundant in the outer margins of trans-cisternae, IRX9-GFP is abundant in an inner margin of medial-cisternae, and both are absent from cisternal centers. This new concentric circle model of Golgi organization has expanded our understanding of Golgi structure and function and has implications for Golgi function in other cell types and organisms. The second part of this thesis explores problem-solving instruction in undergraduate cell biology classes, by testing how different teaching techniques affect student attitudes and performance. These results demonstrate that worked examples can be effective teaching techniques for cell biology problem-solving, with lower-performing students seeing greater benefits. Furthermore, providing worked examples did not ameliorate student desires for answer keys to practice problems. This work can be used to guide the appropriate level of instructional support for students of different expertise levels in future courses, and across curricula.
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