Date Approved
5-7-2026
Graduate Degree Type
Thesis
Degree Name
Cell and Molecular Biology (M.S.)
Degree Program
Cell and Molecular Biology
First Advisor
Mark P. Staves
Second Advisor
Sheila A. Blackman
Third Advisor
Matthew J. Christians
Academic Year
2025/2026
Abstract
There are two dominant models of gravity perception in plant cells: the starch statolith model (in which sedimenting starch grains act as the gravity sensor) and the gravitational pressure model (in which the entire protoplast acts as the gravity sensor). While previous physiological studies demonstrated that the gravitational pressure model better explains the observed phenomena, we would like to follow up with physiological and genetic experimentation with a novel experimental model and model organism, allowing comparison of plant responses in an environment that mimics microgravity to plant responses on the International Space Station (ISS). To do this, we developed two methods. First, we developed a Rotatable Hydroponic Root Observation Box (RoHyROB) that allows observation of gravitropic response in roots rotated perpendicular to the gravitational axis in liquid cultures of varying densities. Oryza roots were tested first to replicate previous density experiments and confirm that the RoHyROB is an effective tool for changing the density of the external medium and gravistimulation. Subsequently, Columbia (Col-0) and phosphoglucomutase mutant (pgm-1) Arabidopsis were then grown in the RoHyROB to assess the effect of extracellular density modulation on a prolifically investigated model organism. Additionally, Col-0 and pgm-1 seeds were grown vertically in media of varying densities under unidirectional red light. Curvature relative to the gravity vector was measured from time-lapse images or root traces in both experimental models. Finally, RNA-seq from gravistimulated Oryza roots grown at varying media densities was used to compare genetic regulation in our model experimental conditions with that observed in simulated and real microgravity on the ISS.
The RoHyROB successfully replicated previous Oryza experiments that support the gravitational pressure model as the predominant model of gravitropic perception. Transcripts related to reactive oxygen species (ROS) management, cell wall modification and heat shock proteins (HSPs) were differentially expressed in Oryza roots grown in dense media compared with control, consistent with observations in microgravity. While the experimental results in Oryza support the gravitational pressure model, RoHyROB and red-light experiments in Arabidopsis did not. Taken together these results suggest that the gravitational pressure model may not be the primary mechanism of gravitropism across all species.
ScholarWorks Citation
Shutz, Kyle D., "Can Dense Media Reduce Gravitational Perception and Mimic Microgravity in Roots?" (2026). Masters Theses. 1176.
https://scholarworks.gvsu.edu/theses/1176
