Recent evidence has indicated that the availability of iron may limit phytoplankton biomass and primary production in many oceanographic regions. Iron is a key component of the photosynthetic electron transport chain; reductions in the rate and efficiency of photosynthesis are expected when phytoplankton growth is iron-limited. In the fellowship research, biophysical, biochemical and immunological techniques will be used to examine the phenotypic response of the photosynthetic apparatus of marine phytoplankton to iron deficiency under controlled conditions in iron-limited chemostat cultures. Interspecific comparisons will be made between organisms from two taxonomic groups, a diatom and a coccolothophorid. The concentrations of the PS I reaction center chlorophyll (P700), the cytochrome b complex and the soluble electron carriers ferredoxin and flavodoxin will be measured spectrophotometrically. Oxygen flash yields will be used to determine the concentration of active PS II reaction centers, and flash fluorescence techniques will be used to determine the fraction of total PS II reaction centers which are active. Polyclonal antibodies from marine algae or higher plants will be used to determine the relative abundances of the carboxylating enzyme ribulose biphosphate carboxylase, the thylakoid ATP synthetase, several components of the PS II reaction center complex and light harvesting complex proteins.
