Iron Deficiency Promotes the Lack of Photosynthetic Cytochrome c 550 and Affects the Binding of the Luminal Extrinsic Subunits to Photosystem II in the Diatom Phaeodactylum tricornutum .

In the diatom Phaeodactylum tricornutum , iron limitation promotes a decrease in the content of photosystem II, as determined by measurements of oxygen-evolving activity, thermoluminescence, chlorophyll fluorescence analyses and protein quantification methods. Thermoluminescence experiments also indicate that iron limitation induces subtle changes in the energetics of the recombination reaction between reduced Q B and the S 2 /S 3 states of the water-splitting machinery. However, electron transfer from Q A to Q B , involving non-heme iron, seems not to be significantly inhibited. Moreover, iron deficiency promotes a severe decrease in the content of the extrinsic PsbV/cytochrome c 550 subunit of photosystem II, which appears in eukaryotic algae from the red photosynthetic lineage (including diatoms) but is absent in green algae and plants. The decline in the content of cytochrome c 550 under iron-limiting conditions is accompanied by a decrease in the binding of this protein to photosystem II, and also of the extrinsic PsbO subunit. We propose that the lack of cytochrome c 550 , induced by iron deficiency, specifically affects the binding of other extrinsic subunits of photosystem II, as previously described in cyanobacterial PsbV mutants.