Electronic Theses and Dissertations

Date of Award


Document Type


Degree Name

M.S. in Biological Science



First Advisor

John Z. Kiss

Second Advisor

Sarah J. Liljegren

Third Advisor

Jason Hoeksema

Relational Format



The aim of this research was to understand mutualistic relationships between plants and endophytic microbes under the influence of an altered gravity vector. Understanding the outcome of the plant-microbe symbiosis in altered gravity is vital to developing life support systems for long distance space travel and colonization of other planets. This research utilized the model tripartite relationship among Medicago truncatula–Sinorhizobium meliloti–Rhizophagus irregularis. Plants were inoculated with rhizobial bacteria (S. meliloti), arbuscular mycorrhizal fungi (R. irregularis), both microbes, or none (microbial control), and placed on a rotating clinostat for 28 d. Vertical and horizontal static controls were also performed. Plant development was quantified and root morphology was measured using the program GiA Roots and nodule numbers and size were counted and measured in Image J. AMF colonization was quantified using Alexa Fluor 488 and the magnified intersection method. Clinorotation significantly reduced M. truncatula dry mass and fresh mass compared to the static controls. The addition of rhizobia treatments under clinorotation altered total root length and root to shoot fresh mass ratio. Nodule size decreased under rhizobia + clinorotation treatment, and nodule density was significantly decreased compared to the vertical treatment. Thus, clinorotation significantly affected M. truncatula and its symbiotic relationships with S. meliloti and R. irregularis . In the long term, the results observed in this clinostat study on the changes of the plant-microbe mutualism need to be verified in spaceflight experiments. Thus, careful consideration of the symbiotic microbes of plants needs to be included in the design of bioregenerative life support systems needed for space travel.

Included in

Biology Commons



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