Organization and Function of Chlorophyll in Membranes of Cyanobacteria during Iron Starvation

Abstract

Cells of Anacystis nidulans strain R2 and of Synechococcus cedrorum were grown in an Fe-deficient medium. Fe starvation induced several pronounced effects without influencing the viability of these cells. The phycocyanin and chlorophyll contents of these cells were depressed, and the absorption maxima of membrane-bound chlorophyll was blue-shifted by 5 nm. Cells showed a dramatic increase in original and in maximal chlorophyll fluorescence when monitored at room temperature. Low temperature chlorophyll fluorescence revealed a loss in fluorescence at 696 and 716 nm; much of the remaining fluorescence emission was at 686 nm. These changes suggest an alteration of membrane composition and structure. This was documented by an electrophoretic analysis of Fe-deficient membranes. Large chlorophyll-protein complexes were not observed in Fe-deficient membranes, although the chlorophyll-binding proteins were present. The staining of acrylamide gels with 3,3'',5,5''-tetramethylbenzidine plus peroxide indicated that Fe deficiency led to a decrease in the quantity of cytochromes. These results support a structural model of the relation between fluorescence and chlorophyll organization in Anacystis. In addition, they suggest a method for studying cytochrome and chlorophyll protein assembly in these membranes.