Lindsay Ann Lawreck

Major: Biology

University Honors with Honors in Biology

Supervisor: Dr. Alison Taylor

THE ROLE OF THE ENDOPLASMIC RETICULUM IN CALCIFICATION IN THE COCCOLITHOPHORE, C.PELAGICUS

Coccolithophores are single-celled photosynthetic marine protists that are distinguished by calcium carbonate plates, called coccoliths, surrounding their exterior. They are found in both open and coastal waters, are the most abundant calcifying algae, and play critical roles in marine biogeochemical cycles. Production of coccoliths is dependent on the uptake of free calcium from the external seawater and subsequent intracellular storage and transport to a specialized Golgi-derived coccolith vesicle. The formation of coccoliths requires supersaturation of calcium in the coccolith vesicle and also requires a well-controlled calcium homeostasis mechanism. To what degree intracellular stores of calcium are used to facilitate calcification is currently unknown. The goal of this study is to test the hypothesis that during coccolithophore calcification, calcium is transported into the cell and stored in the endoplasmic reticulum where it can readily supply the coccolith vesicle for calcification. The hypothesis was tested by treating C. pelagicus cells with different SERCA pump inhibitors to disrupt the endoplasmic reticulum stores of calcium and then observing the effects that these treatments had on the abundance and appearance of subsequently produced coccoliths. The data obtained from these experiments show that SERCA inhibitors caused a significant increase in the production of the aberrant coccoliths, which supports the hypothesis. A second type of coccolith that had normal crystal growth but was incomplete was observed as frequently in the control as the treatments, suggesting that these may naturally occur and that SERCA inhibitors are not the main cause of their production.