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

Abstract

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.

Sustained net CO2 evolution during photosynthesis by marine microorganism

“…The significance of this energy-dependent Ci circulation, apparently futile, and its possible role is yet to be established, but it could confer some protection against damage to the photosynthetic reaction center occasioned by excess light energy. The large cross-section of the light-energyabsorbing pigments, following acclimation to a low light intensity [16,18], renders the photosynthetic machinery susceptible to photodamage at higher light intensities [17,19,20]. The observation that, at a saturating light intensity, net HCO 3 uptake was six-fold larger than CO 2 fixation raises the possibility that Ci cycling may serve as a A comparison of the rates of photosynthetic O 2 evolution, net CO 2 efflux and calculated net HCO 3 influx in Synechococcus sp.…”

“…Most of the studies reported here were carried out on Synechococcus sp. WH7803, which is capable of growing under a wide range of light intensities by modulating the amount of phycoerythrin and hence the light-harvesting cross-section [15][16][17][18][19]. Further, when exposed for about an hour to light intensities supraoptimal for photosynthesis, it has the ability to lower the efficiency of energy transfer from the harvesting complex to the photosynthetic reaction center.…”

Nitrogen starvation in marine Synechococcus strains: clonal differences in phycobiliprotein breakdown and energy coupling

“…We predicted that energy absorbed by phycoerythrln (PE) in strains that conserved the pigment would have to be dissipated by some mechanism in order to reduce the amount of energy reaching the photosystems as photosynthesis became feedback inhibited. Work of Barlotv & Alberte (1987) suggested that this may be accomplished by an increased fluorescence yield of the PBPs as was shown in Synechococcus sp. WH7803 when exposed to a shift-up in light intensity, a condition that causes a simi.lar imbalance in the flow of energy through the photosynthetic apparatus.…”

ACCLIMATION OF SYNECHOCOCCUS STRAIN WH7803 TO AMBIENT CO2 CONCENTRATION AND TO ELEVATED LIGHT INTENSITY1

“…This has been attributed to variation in the composition of the phycobilisomes; that is a larger PE/PC ratio in cells grown under low light intensity. On the other hand, when cells grown at 25 pmol quanta.m-2.s-' were exposed to 1500 pmol quanta.m-2.s-1 for 3 h, the maximal photosynthetic rate decreased significantly (Barlow and Alberte 1987). This decline was accompanied by a rise in the ratio between the fluorescence intensities of PE/Chl a and a decrease in the level of P,oo per cell.…”

“…Laboratory studies on Synechococcus WH7803 demonstrated a large decline in the ratio of PE to chlorophyll a (Chl a) when the light intensity experienced by the cells during growth was raised (Kana and Glibert 1987a). Changes in the cellular abundance of P71,1) (as indicated by the extent of the P7"" signal) following growth under various light intensities have also been reported (Barlow andAlberte 1985, 1987).…”