Doctor of Philosophy (PhD)


Biological Sciences

Document Type



Carbonic anhydrases (CAs) are zinc-metalloenzymes that interconvert two inorganic carbon (Ci) species, CO2 and HCO3-. In Arabidopsis thaliana, there are eight Alpha-CA genes, six Beta-CA genes, three Gamma-CA genes, and two Gamma-CA-like genes. The majority of CA research in plants has focused on finding a link between CA activity and photosynthesis rates. Since the CA genes are expressed in different plant tissues and multiple CA isoforms are distributed among various organelles of the plant cell, I hypothesize that CAs facilitate CO2 diffusion among cell compartments and maintain Ci pools for carbon-requiring reactions by interconverting CO2 and HCO3-. This thesis focuses on the Alpha-CAs and Beta-CAs of Arabidopsis and how they may affect various reactions throughout the plant. CA T-DNA insertion lines were used to determine if removing one or more CAs from Arabidopsis affects the plant growth. The Beta-ca5 single mutant and Beta-ca2Beta-ca4, Alpha-ca1Beta-ca4, and Alpha-ca2Beta-ca4 double mutants show different growth phenotypes. The Beta-ca2Beta-ca4 plants were smaller in size and chlorotic in their younger leaves under low CO2 conditions, but showed improved growth in high CO2 conditions. The growth of the Beta-ca5 single mutant was severely stunted in ambient CO2 conditions and high CO2 partially rescued wildtype growth in the Beta-ca5 plants. The Alpha-ca1Beta-ca4 and Alpha-ca2Beta-ca4 double mutants were slightly smaller than wildtype plants in low CO2 conditions. Interestingly, it seems the reduced growth of the Beta-ca5 single mutant and Beta-ca2Beta-ca4 double mutant plants was not linked to deficiencies in photosynthesis rates but rather may be required for other carbon requiring reactions. These results suggest that CAs are playing more complex roles in plants than once thought and that the various isoforms are affecting different carbon-requiring pathways.



Document Availability at the Time of Submission

Student has submitted appropriate documentation to restrict access to LSU for 365 days after which the document will be released for worldwide access.

Committee Chair

Moroney, James V.