The nab1 gene product is important for light-induced state transitions in Chlamydomonas reinhardtii

Mussgnug JH, Kapazoglou A, Mullineaux CW, Nixon PJ, Kruse O. The nab1 gene product is important for light-induced state transitions in Chlamydomonas reinhardtii. In: Photosynthesis: Fundamental aspects to global perspectives, 13th International Congress on Photosynthesis, Montreal, Alliance Communication Group. Alliance Communication Group; 2004

Var2 mutation in Arabidopsis affects D1 degradation

Var2 is one of several FtsH homologues in Arabidopsis thaliana. Var2 mutations cause variegation, and alter photosynthetic function in a number of ways. FtsH proteins are AAA proteases (ATPases associated with a variety of cellular activities), which are widely distributed in prokaryotes and eukaryotes and have numerous roles. We have found that Var2 mutant are affected in the D1 repair cycle following photoinhibition. Composition of the photosynthetic apparatus is comparable in wild-type (WT). The chlorophyll a/b ratios suggest similar-size photosystem (PS) I1 antennae, and fluorescence spectra indicate only slightly different PS1:PSII ratios in low-light-grown plants. Measurement of Fv/Fm, however, suggests that Var2 undergoes greater photoinhibition than WT at low (300 kE/mZ/s) and, markedly, high light (1800 pE/mZ/s). When protein synthesis is prevented (with lincomycin), both Var2 and WT leaves are photoinhibited at high light since neither can synthesise new D1 polypeptide following photooxidative damage. Even without lincomycin, however, Var2 is photoinhibited to twice the extent of WT this key PSII protein is not replaced. Western blots confirm that lincomycin-treated WT leaves exhibit rapid D1 turnover whereas Var2 leaves do not, suggesting that D1 is not degraded

P-700 photooxidation in state 1 and state 2 in cyanobacteria upon flash illumination with phycobilin- and chlorophyll-absorbed light

We have measured the flash yield of P-700 photooxidation in cells of the cyanobacteria Synechococcus 6301 and Nostoc MAC adapted to light-states 1 and 2. Using excitation at 337 nm, the flash yield of P-700 photooxidation at limiting flash intensity was larger in state 2 in both species, indicating an increased absorption cross-section of PS I in state 2 for light absorbed by both chlorophyll and phycobilin pigments. Using excitation at 532 nm, the flash yield of P-700 photooxidation at limiting intensity was also larger in state 2 in both species, indicating an increased absorption cross-section of PS I for light absorbed specifically by phycocyanin or phycoerythrin. Differences in P-700 re-reduction kinetics between states 1 and 2 were consistently observed following flash excitation at either wavelength. Our results are consistent with a model for redistribution of excitation energy in state 2 that involves decoupling of the phycobilisome from PS II and its functional reassociation with PS I. Photosynthesis; Light harvesting; Photosystem I; State transition; Phycobilisome; Excitation energy distribution; Cyanobacteria; ( Nostoc MAC; Synechococcus 6301