UBC Theses and Dissertations
The relationship between irradiance (quantity, quality and photoperiod), sinking rate and carbohydrate content in two marine diatoms Fisher, Anne Elizabeth
Diatoms are physiologically able to control their sinking rates through the selective accumulation of lighter ions in the vacuole (an energy-requiring process). The extent to which a diatom needs to physiologically control its sinking rate will depend on its excess density (i.e. the degree to which the cell is denser than seawater). The excess density of a diatom, and thus the amount of energy required to maintain a low sinking rate, might change with the carbohydrate content of the cells. The purpose of this work was to simultaneously measure sinking rate and carbohydrate content in 2 marine diatoms (Thalassiosira weissflogii and Ditylum brightwellii) to see if sinking rate is affected by irradiance driven changes in carbohydrate content. In the first set of experiments, carbohydrate content was varied by growing cells on light/dark cycles under high and low light. Sinking rate measurements (SETCOL method) were made at the end of the light period and the end of the dark period. Sinking rates were measured on live and heat-killed cells in order to compare the inherent sinking rate of the cell (determined by ballast) to the physiologically-determined sinking rate. In the second set of experiments, carbohydrate content was varied by growing cells under continuous red, white or blue light. Sinking rate was not positively correlated to carbohydrate content in T. weissflogii or D. brightwellii grown on light/dark cycles under low or high white light. Sinking rate in D. brightwellii was under physiological control in all experiments, but in T. weissflogii physiological sinking rate control was intermittent. D. brightwellii showed diel changes in buoyancy, with higher sinking rates at the end of the dark period than at the end of the light period, when cells were positively buoyant. T. weissflogii had higher sinking rates when grown under red light than under white or blue light, but there were no differences in carbohydrate content. D. brightwellii contained twice as much carbohydrate when grown under red light than under white or blue light, but there were no differences in sinking rate.
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