Assembly of Chl-Protein Complexes in Membranes of Iron-Stressed Synechococcus SP. PCC7942 Proceeds in the Absence of Chlorophyll Synthesis

Abstract

Iron-limited growth of plants and cyanobacteria results in a dramatic decrease in chlorophyll and thylakoid content. Iron deficient cells of the cyanobacterium Synechococcus sp. PCC7942 demonstrate significant changes in the organization of their photosynthetic membranes. One of the most dramatic changes is evidenced by the depletion of PSI and PSH chlorophyll-protein complexes and the accumulation of an accessory chlorophyll-protein complex, CPVI-4, which is present in very low amounts in unstressed cells. CPVI-4 harbors the majority of the chlorophyll in the iron-stressed cells. Its function may be that of a weak antenna or perhaps that of a chlorophyll reservoir which facilitates recovery when iron becomes available (Riethman and Sherman, 1988). We examined the recovery of cells from iron limitation by monitoring low temperature chlorophyll fluorescence of whole cells and chlorophyll-protein changes in thylakoid membranes under conditions in which chlorophyll synthesis or protein synthesis is inhibited.