Accumulation of ferredoxin and flavodoxin in a marine diatom in response to Fe

Despite recognition that Fe availability is significant in regulating ocean ic production in some regions, the biogeochemistry of this trace element is poorly understood. To complement contemporary methods of analytical chemis try, we have used an immunological approach to monitor the Fe nutrition of marine phytoplankton. In prokaryotes and numerous microalgae, the redox cat alyst ferredoxin is functionally replaced by flavodoxin during periods of F e deficiency. In this study, antibodies were raised against ferredoxin puri fied from a marine diatom, and their utility as a diagnostic indicator was assessed. A species survey demonstrated broad reactivity with both pennate and centric diatoms and additionally with several nondiatom taxa. In batch cultures of the diatom Phaeodactylum tricornutum Bohlin, in which Fe levels were varied, accumulation of ferredoxin varied with the physiological stat e of the culture; in unimpaired cells (F-v/F-m greater than or equal to 0.6 5), ferredoxin levels were high, whereas levels dropped markedly in cells e xperiencing even slight photochemical impairment. Accumulation of flavodoxi n varied inversely with that of ferredoxin. An experiment was performed to demonstrate the temporal pattern of accumulation of ferredoxin upon recover y from Fe limitation. Prior to Fe amendment, cells were physiologically imp aired (chlorotic, F-v/F-m < 0.3) and contained flavodoxin but no detectable ferredoxin. Following addition of Fe, constraints on photochemistry were r elaxed within hours. Coinciding with this, levels of flavodoxin declined, w hereas ferredoxin was accumulated to high levels within 8 h.