Erin Horning

Date Approved


Degree Type

Open Access Senior Honors Thesis

Department or School



Decreased crop yield as a result of insufficient freshwater supply is a distressing problem in world agriculture today. Plants lose water via transpiration through pores located in the epidermis on the underside of the leaf referred to as stomata. The aperture of such a pore is regulated by two adjacent guard cells that swell and subside as water follows ions that are pumped into and from the cell in response to changing environmental conditions. Our hypothesis that one of the six NADP-malic enzyme isoforms in Arabidopsis thaliana is guard-cell specific and plays a role in the mechanism of closing the stomata was tested by isolating guard cell mRNA from A. thaliana and determining the relative expression of the six NADP-ME isoforms in whole leaves and guard cell protoplasts via RT-PCR. The optimization of a guard cell protoplast isolation protocol allowed for the use of very pure mRNA in these experiments. Our results suggested that all six of the NADP-ME isoforms in A. thaliana are expressed in whole leaves, and that but at2g19900 are expressed in the guard cell protoplasts. There was no evidence of a guard cell-specific isoform. Additionally, we conducted a phylogenetic analysis of malic enzyme sequences among plant species in order to test the hypothesis that the C4 form of malic enzyme evolved independently from the forms found in C3 plants. This hypothesis was supported by our preliminary phylogenetic analysis. 3