Dynamic responses of photosystem II and phycobilisomes to changing light in the cyanobacterium Synechococcus sp. PCC 7942

Abstract

Abstract.We have examined the molecular and photosynthetic responses of a planktonic cyanobacterium to shifts in light intensity over periods up to one generation (7 h). Synechococcus sp. PCC 7942 possesses two functionally distinct forms of the D 1 protein, D 1:1 and D 1:2. Photosystem II (PSII) centers containing DI:I are less efficient and more susceptible to photoinhibition than are centers containing Dl:2. Under 50 ~tmol photonsm -2-s -1, PSII centers contain DI:I, but upon shifts to higher light (200 to 1000 ~tmol photons 9 m -2 9 s-l), DI:I is rapidly replaced by D1:2, with the rate of interchange dependent on the magnitude of the light shift. This interchange is readily reversed when cells are returned to 50 ~tmol photons, m -2. s -1. If, however, incubation under 200 ~tmol photons, m -2. s -1 is extended, DI:I content recovers and by 3 h after the light shift D 1:1 once again predominates. Oxygen evolution and chlorophyll (Chl) fluorescence measurements spanning the light shift and D1 interchanges showed an initial inhibition of photosynthesis at 200 ~tmol photons, m -2. s -1, which correlates with a proportional loss of total D1 protein and a cessation of growth. This was followed by recovery in photosynthesis and growth as the maximum level of D1:2 is reached after 2 h at 200 ~tmol photons 9 m -2 9 s -1. Thereafter, photosynthesis steadily declines with the loss of D 1:2 and the return of the less-efficient D 1:1. During the D 1:1/D 1:2 interchanges, no significant change occurs in the level of phycocyanin (PC) and Chl a, nor of the phycobilisome rod linkers. Nevertheless, the initial PC/Chl a ratio strongly influences the magnitude of photoinhibition and recovery during the light shifts. In Synechococcus sp. E-mail: adrian.clarke @ plantphys.umu.se lates PSII activity to limit damage upon exposure to excess light.

PsaK2 Subunit in Photosystem I Is Involved in State Transition under High Light Condition in the Cyanobacterium Synechocystis sp. PCC 6803

“…PCC 7942, high light induces the interchange between two forms (D1:1 and D1:2) of D1 protein, a reaction center subunit of PSII. D1:1 is predominant under low light condition, and D1:2 increases during acclimation to high light (36). The mutant defective in the gene encoding D1:2 is sensitive to photoinhibition because of the failure to exchange D1:1 for D1:2 (37).…”

The clpP multigene family for the ATP-dependent Clp protease in the cyanobacterium Synechococcus c cThe GenBank accession numbers for the sequences of clpPII-clpX and clpR-clpPIII reported in this paper are U92039 and AJ132005, respectively.

“…All Synechococcus strains were grown on solid or in liquid BG-11 (Clarke et al, 1995). Liquid cultures were grown in 80 ml glass tubes in 37 mC water-baths with continuous light of 70 µmol photons m − # s − " and bubbled with 5% CO # in air (standard growth conditions).…”

The heat shock protein ClpB mediates the development of thermotolerance in the cyanobacterium Synechococcus sp. strain PCC 7942

“…Each culture of the cyanobacterium Synechococcus sp. strain PCC 7942 was grown in BG-11 inorganic medium (32) buffered with 10 mM 3-(N-morpholino)propanesulfonic acid (pH 7.5) at 37ЊC under a continuous photon irradiance of 50 mol m Ϫ2 s Ϫ1 in batch cultures (3). The ⌬clpB strain was maintained on solid BG-11 plates and in liquid precultures, with 5 g of the antibiotic kanamycin added ml Ϫ1 to maintain selection.…”