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Document Type

Open Access

Degree Program

Molecular & Cellular Biology

Degree Type

Master of Science (M.S.)

Year Degree Awarded

2012

Month Degree Awarded

September

Keywords

Brachypodium distachyon, rhythmic growth, vascular development, lignin deposition, crystalline cellulose deposition, plant biomass

Abstract

Plants reduce inorganic carbon to synthesize biomass that is comprised of mostly polysaccharides and lignin. Growth is intricately regulated by external cues such as light, temperature, and water availability and internal cues including those generated by the circadian clock. While many aspects of polymer biosynthesis are known, their regulation and distribution within the stem are poorly understood. Plant biomass is perhaps the most abundant organic substance on Earth and can be used as feedstock for energy production. Various grass species are under development as energy crops yet several of their attributes make them challenging research subjects. Brachypodium distachyon has emerged as a grass model for food and energy crop research. I studied rhythmic growth, a phenomenon important to understanding how plant biomass accumulates through time, and vascular system development, which has biofuel feedstock conversion efficiency and yield. Growth rate changes within the course of a day in a sinusoidal fashion with a period of approximately 24 hours, a phenomenon known as rhythmic growth. Light and temperature cycles, and the circadian clock determine growth rate and the timing of rate changes. I examined the influences of these factors on growth patterns in B. distachyon using time-lapse photography. Temperature and, to a lesser extent, light influenced growth rate while the circadian clock had no noticeable effect. The vascular system transports important materials throughout the plant and consists of phloem, which conducts photosynthates, and xylem, which conducts water and nutrients. The cell walls of xylem elements and ground tissue sclerenchyma fibers are comprised of cellulose, hemicelluloses, and lignin. These components are important to alternative energy research since cellulose and hemicellulose can be converted to liquid fuel, but lignin is a significant inhibitor of this process. I investigated vascular development of B. distachyon by applying various histological stains to stems from three key developmental. My results described in detail internal stem anatomy and demonstrated that lignification continues after crystalline cellulose deposition ceases. A better understanding of growth cues and various anatomical and cell wall construction features of B. distachyon will further our understanding of plant biomass accumulation processes.

file 1.lua (4 kB)
File 1.

Movie 1. Leaf growth in ligh dark and temperature cycle conditions (LdHc).wmv (6332 kB)
Movie 1. Leaf growth in ligh dark and temperature cycle conditions (LdHc)

Movie 2. Leaf growth in ligh dark and temperature cycle conditions (LdHc).wmv (5989 kB)
Movie 2. Leaf growth in ligh dark and temperature cycle conditions (LdHc)

Movie 3. Leaf growth in constant conditions (LLHH).wmv (10998 kB)
Movie 3. Leaf growth in constant conditions (LLHH)

Movie 4. Leaf growth in constant conditions (LLHH).wmv (10622 kB)
Movie 4. Leaf growth in constant conditions (LLHH)

Movie 5. Leaf growth in constant conditions (ddHH).wmv (5918 kB)
Movie 5. Leaf growth in constant conditions (ddHH)

Movie 6. Leaf growth in constant conditions (ddHH).wmv (6896 kB)
Movie 6. Leaf growth in constant conditions (ddHH)

Movie 7. Leaf growth in light dark and constant temperature conditions (LdHH).wmv (3575 kB)
Movie 7. Leaf growth in light dark and constant temperature conditions (LdHH)

Movie 8. Leaf growth in light dark and constant temperature conditions (LdHH).wmv (4075 kB)
Movie 8. Leaf growth in light dark and constant temperature conditions (LdHH)

Movie 9. Leaf growth in light dark and constant temperature conditions (Ldcc).wmv (5577 kB)
Movie 9. Leaf growth in light dark and constant temperature conditions (Ldcc)

Movie 10. Leaf growth in light dark and constant temperature conditions (Ldcc).wmv (6231 kB)
Movie 10. Leaf growth in light dark and constant temperature conditions (Ldcc)

Movie 11. Leaf growth in constant light or dark with temperature cycles (LLHc).wmv (6128 kB)
Movie 11. Leaf growth in constant light or dark with temperature cycles (LLHc)

Movie 12. Leaf growth in constant light or dark with temperature cycles (LLHc).wmv (7259 kB)
Movie 12. Leaf growth in constant light or dark with temperature cycles (LLHc)

Movie 13. Leaf growth in constant light or dark with temperature cycles (ddHc).wmv (6152 kB)
Movie 13. Leaf growth in constant light or dark with temperature cycles (ddHc)

Movie 14. Leaf growth in constant light or dark with temperature cycles (ddHc).wmv (6341 kB)
Movie 14. Leaf growth in constant light or dark with temperature cycles (ddHc)

Movie 15. Leaf growth in inverted light dark and temperature cycles (LdcH).wmv (5445 kB)
Movie 15. Leaf growth in inverted light dark and temperature cycles (LdcH)

Movie 16. Leaf growth in inverted light dark and temperature cycles (LdcH).wmv (5560 kB)
Movie 16. Leaf growth in inverted light dark and temperature cycles (LdcH)

 

Advisor(s) or Committee Chair

Hazen, Samuel P