Portland State University. Environmental Sciences and Resources Ph. D. Program
John G. Rueter
Date of Award
Doctor of Philosophy (Ph.D.) in Environmental Sciences and Resources: Biology
School of the Environment
1 online resource (xv, 191 pages)
Cyanobacteria -- Photoadaptation -- Effect of iron concentration on, Photosynthetic bacteria, Light -- Physiological effect, Chlorophyll -- Synthesis
The marine cyanobacterium Synechococcus WH7803 adapts to changes in light intensity by changing its photosynthetic physiology. This work is a study o f the rate o f photoadaptation of Synechococcus WH7803 in laboratory cultures. Cultures were shifted from constant 8 µEm-2s-1 light to constant 80 µEm-2s-1 light, from constant 80 µEm-2s-1 light to 8 µEm-2s-1 light and from different light regimes to a single fluctuating light regime. The response of high iron cultures grown in modified aquil culture medium at 5*10-6M Fe was compared with the response of low iron cultures grown in modified aquil medium at 1*10-6M Fe. Cultures were assayed every 2 days for at least 10 days, assaying cell population density by fluorescence microscopy, chlorophyll a by spectrophotometry of acetone extracts, total protein by the bicinchoninic acid method, and photosynthesis vs. irradiance (P vs. I) response by H14CO3 uptake at 10 light intensities.
Iron nutrition did not strongly affect the rate of photoadaptation as determined from the slopes of P vs. I curves as light approaches zero (the parameter called alpha). The rate of chlorophyll a synthesis was the parameter most strongly affected by iron nutrition, slowing in restricted iron medium. Based on alpha per cell, the adaptation time to the shift from constant 8 µEm-2s -1 light to constant 80 µEm-2s -1 light was less than 2 days. Based on other culture parameters the time to complete adaptation may be closer to 8 days. Based on alpha per cell, the adaptation time to the shift from constant 80 µEm-2s -1 light to constant 8 µEm-2s -1 light was on the order of 2 days. Based on other culture parameters the time to complete adaptation may exceed 10 days.
Moulton, Jon Daniel, "Photoadaptation Rate of Synechococcus WH7803 Cultures at Two Iron Concentrations" (1998). Dissertations and Theses. Paper 3070.