Date of Award

1996

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Plant Pathology and Crop Physiology

First Advisor

Mary E. Musgrave

Abstract

The best strategy for providing food and maintaining the environment on long-duration space missions is a bioregenerative life support system based on the growth of higher plants. Before such a system can be implemented, a better understanding of plant growth in space will have to be achieved. Little is known about the role of gravity-dependent physical processes in normal physiological function. A series of ground-based and spaceflight experiments was conducted to examine root oxygen availability in microgravity nutrient delivery systems. In spaceflight experiments Arabidopsis thaliana (L.) Heynh. plants were analyzed for changes in root medium redox potential and root alcohol dehydrogenase (ADH) activity, localization, and expression. These experiments showed ADH activity and expression increased by 89% and 136% respectively, without any change in localization. Ground experiments demonstrated the increase in ADH activity in spaceflight roots was achieved by a 28% decrease in oxygen availability. Metabolic and growth pattern changes in spaceflight roots suggested that root orientation could be directed toward oxygen (oxytropism). Both gravity sensing and agravitropic Pisum sativum L. roots reoriented toward oxygen when grown in a microrhizotron that maintains an oxygen gradient over the whole range of subambient oxygenation, although the rate of reorientation declined as oxygen concentrations decreased. Ground-based experiments to evaluate technologies for growing plants in space were conducted by comparing root system morphology, ADH activity, nutrient content, and general plant growth parameters of Triticum aestivum L. cv Yecora Rojo and Brassica rapa L. A system that maintains a nutrient solution inside of a porous hydrophilic ceramic tube was compared with two passive substrate systems now used for spaceflight research (solidified agar-gel and phenolic foam media). Plants performed best on the porous tube because the roots grow on the tube surface in contact with air and nutrient solution. Oxygenation is important for normal root function in space, as on earth. Two obstacles restricting development of plant nutrient delivery technologies are a limited knowledge of the requirements of plants in space, and an incomplete understanding of plants in general. Information concerning the changes in oxygenation during spaceflight should allow scientists and engineers to address these problems.

ISBN

9780591288773

Pages

150

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