Bioenergetic processes are modified during nitrogen starvation and recovery in Phormidium laminosum (Cyanophyceae)

In the non-N-2-fixing cyanobacterium Phormidium laminosum (Agardh) Gomont (strain OH-1-pCl(1)), N starvation induced an increase in the rate of respiration and a decrease in the rate of O-2 evolution. When. NO3- was added to illuminated N-starved cells, O-2 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 pow was maximal under light-saturating conditions and after 2-3 days of N starvation. The respirator 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.