Bioenergetic Processes Are Modified During Nitrogen Starvation and Recovery in Phormidium Laminosum (Cyanophyceae)1

In the non‐N2‐fixing cyanobacterium Phormidium laminosum (Agardh) Gomont (strain OH‐I‐pCl1), N starvation induced an increase in the rate of respiration and a decrease in the rate of O2 evolution. When NO3− was added to illuminated N‐starved cells, O2 evolution immediately increased to levels shown by NO3− grown cells, even though N‐starved cells had lost most of their in vitro photosynthetic activities. Stimulation of noncyclic electron flow was maximal under light‐saturating conditions and after 2–3 days of N starvation. The respiratory rate of N‐starved cells was stimulated by the addition of NO3− or NH4+ and partially inhibited at very low irradiances, even in the presence of DCMU (3‐(3,4‐dichlorophenyl)‐1,1‐dimethylurea). Results indicate that N‐starved cells obtain the energy supply for N assimilation through a process different from that used by N‐sufficient cells. N‐starved cells were able to take up NO3− in the dark and when illuminated in the presence of DCMU under anaerobiosis. Following NO3− addition, the photosynthetic yield of the in vivo noncyclic electron transport slightly increased, whereas it decreased after NH4+ addition. Addition of NO3− or NH4+ favored photoinhibition of photosystem II, the effect being faster after NH4+ addition.