Photosynthetic characteristics of phycoerythrin-containing marine Synechococcus spp. II. Time course responses of photosynthesis to photoinhibition

Marine Synechococcus spp.optimize growth and photosynthesis at low light levels and show photoinhibition of photosynthesis at high levels.We exam~ned the photosynthetic response to, and recovery from, exposure to photoinhibitory light levels after growth at low photon flux densities in 2 clones of Synechococcus spp.Clones WH 7803 and WH 8018 were grown at 25 pE m-' S-', exposed to photoinhibitory light (1500 pE m-' S-') for 3 h, and then returned to the growth light level.Clone WH 7803 showed a 40 % decrease in P, , , while Clone WH 8018 showed a 30 % decrease during the exposure.This was accompanied by a proportional increase in whole-cell phycoerythrin fluorescence and by a decrease in the cellular content of P700, the photochemical reaction center of Photosystem I. On return to low light, photochemically active P700 recovered to pre-photoinhibitory levels within 1 h in Clone WH 8018 and within 2 h in Clone WH 7803.Photosynthetic rates and phycoerythrin fluorescence required 2 to 3 h and 3 to 4 h to recover in Clones WH 8018 and WH 7803, respectively.During exposure and recovery, no changes in cellular levels of chlorophyll or phycobiliproteins were observed.It is concluded that (1) the primary deleterious effect of photoinhibition of photosynthesis was reversible losses in Photosystem I activity, and (2) recovery from photoinhibition was rapid and occurred within hours.