Date of Award


Degree Name

Biological Sciences


College of Science

Type of Degree


Document Type


First Advisor

Jagan V. Valluri

Second Advisor

Marcia Harrison

Third Advisor

Elizabeth Murray


This thesis research investigates the regulation of gene expression in pea stems (Pisum sativum) after changes in orientation to gravity (gravistimulation). Specifically, this project examines the changes in extracellular soluble proteins due to gravistimulation in pea seedlings. This change in gravity alters the cellular growth pattern, which can be directly linked to enzymatic activity resulting in the expression of cell wall loosening proteins called expansins. This loosening of the cell wall matrix subsequently increases elasticity in growing cells, thus leading to an upward curvature of the stems. These changes in enzymatic activity and gene expression are crucial for the survival of plants when variations in environmental conditions occur.

The methods utilized in this project were performed in order to determine whether or not expansin genes are up-regulated during gravistimulation, and if the pea expansin gene family is highly conserved throughout the plant kingdom. Proteins were first extracted from the cell walls of peas at various times during gravistimulation (0 hrs. - 48 hrs.) and analyzed using SDS PAGE. Standard molecular techniques were also utilized in which, 1) the probe used to identify the expansin genes was created using RT-PCR, 2) a DNA library for Pisum sativum was created and screened for the presence of expansin genes, 3) standard Northern blotting techniques were applied to pea RNA extracted at various times during gravistimulation (0 hrs. - 48 hrs.) The results of this thesis found that the cell wall expansin genes were probably up-regulated during specific times of gravistimulation (i.e. 24 hours). However, due to the degeneracy of the expansin probe there is the possibility that more than one gene is being hybridized, thus decreasing our confidence in these results. In conclusion, these experiments must be repeated with a more specific probe to determine whether expansins do indeed exist in Pisum sativum and if they are being up-regulated.


Cells - Growth - Effect of gravity on.

Proteins - Research.