Degree Type

Dissertation

Date of Award

2009

Degree Name

Doctor of Philosophy

Department

Genetics, Development and Cell Biology

First Advisor

Eve S. Wurtele

Abstract

Acetyl-CoA is found at the center of metabolism. This important metabolite is utilized within the cytosol of the plant for the biosynthesis of a large battery of important compounds via carboxylation, condensation or acetylation. The compounds that result from these three reactions include but are not limited to: flavonoids, sterols, elongated fatty acids utilized in cuticle and seed oil biosynthesis, mevalonate-derived isoprenoids, and specialized phytochemicals synthesized by polyketide synthases (PKS). The enzyme that synthesizes the cytosolic pool of acetyl-CoA is ATP-Citrate Lyase (ACL). When ACL activity is reduced in Arabidopsis thaliana, the resultant phenotype consists of a small, bonsai appearance, dark green leaves, hyper-accumulation of starch and anthocyanins and reduced accumulation of cuticular wax. Antisense-ACLA plants receiving malonate treatment do not hyper-accumulate starch or anthocyanins and they appear more wildtype (WT) in appearance. Transcriptomic and metabolomic data reveals large differences in antisense-ACLA plants and WT plants, but very few changes in antisense-ACLA plants treated with water as compared to those receiving malonate.

Acetyl-CoA is utilized for the production of a number of specialized phytochemicals. Within the species Hypericum, a number of acetyl-CoA derived phytochemicals having bioactivity in mammalian systems have been identified including hypericin and hyperforin. Hypericum gentianoides was utilized as a medicinal plant by Native American Cherokees. Extracts from H. gentianoides have the ability to reduce the infectivity of HIV in HeLa37 cells and alter calcium hoeostatsis of HEK293 cells. The bioactive extracts contain several unusual acyl-phloroglucinols, saroaspidin A, uliginosin A and hyperbrasilol C. Saroaspidin A, uliginosin A and hyperbrasilol C accumulate in translucent glands found on the surface of H. gentianoides. The translucent glands found on H. gentianoides develop schizogenously, i.e., secretory cells within the gland pull away from each other in order to create an open cavity to store secretory product. As translucent glands age, changes in secretory cell wall integrity, plastid numbers, mitochondrial activity and cytoplasm density occur. Early in gland development, glands are surrounded by heavily osmium-stained material within peripherial cells and surrounding tissues, and presumably this staining becomes reduce over time as the chemical composition of both the surround tissues and glands changes.

Acetyl-CoA is critical to the synthesis of important primary and specialized phytochemicals, and understanding the production and utilization of this metabolite is necessary.

Copyright Owner

Heather Leigh Babka

Language

en

Date Available

2012-04-30

File Format

application/pdf

File Size

245 pages

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