fluorescence; nitrogen metabolism; Phormidium laminosum; photosynthesis; state transitions
Abstract :
[en] In an attempt to clarify the interactions between the available nitrogen source and the photosystems in cyanobacteria, O-2 exchange and fluorescence emission were monitored in spheroplasts and intact cells of the non N-2-fixing cyanobacterium Phormidium laminosum (strain OH-1-p.Cl-1) growing on different nitrogen sources or in the absence of nitrogen. Short-term (time scale of seconds to minutes), NH4+ addition to NO3--growing or N-starved cells and, to a minor extent, NO3- addition to N-starved cells, induced state 2 transitions both in light and dark. Long term (time scale of days), the fluorescence yield of PSI relative to that of PSII at 77 K was higher in NO3-- than in NH4-+ growing cells, and even higher in N-starved cells. In the dark, the plastoquinone pool was more reduced in NH4-+ than in NO3--growing cells. Both PSII and PSI activities and the degree of linking between both photosystems were affected in the long term, so that non-cyclic electron transport decreased in parallel to the ferredoxin requirement to assimilate each nitrogen source. Results indicate that nitrogen metabolism exerts short- and long-term control over the photosynthetic apparatus, which acclimates to the energy requirement of the available nitrogen source.