Ultrastructure and photosynthetic apparatus of Rhodella violacea (Porphyridiales, Rhodophyta) grown under iron-deficient conditions

We analyzed the effects of iron deficiency on the ultrastructure and bioche mical composition of the photosynthetic apparatus of the marine alga Rhodel la violacea (Kornmann) Wehrmeyer (Porphyridiales, Rhodophyta). Iron deficie ncy, lasting for up to 12 wk, caused a drastic reduction of the thylakoid s urface area per cell. The chlorophyll content of the cells decreased to app roximately 2% of the original level, whereas the carotenoids were reduced t o about 12%. Photosystem I was severely affected. The ratio of photosystem I to photosystem II decreased in iron-deficient cells from 2.3 to 0.5. Poly peptides of photosystem II and of the light-harvesting complex of photosyst em I were reduced in a nonstoichiometric way. The 77-K fluorescence emissio n maximum of the algae shifted from 716 to 709 nm. Phycobilisomes that were morphologically indistinguishable from those in control cells were present in electron microscopic images even at the final stage of iron starvation. However, the ratio of phycoerythrin to phycocyanin decreased from about 2. 1 to 1.5. Polypeptides corresponding to the cyanobacterial isiA gene produc t were not detected.