A larger transcript is required for the synthesis of the smaller isoform of ferredoxin : NADP oxidoreductase

International audienc

A New Ioxynil-Resistant Mutant in Synechocystis PCC 6714: Hypothesis on the Interaction of Ioxynil with the D1 Protein

International audienceA new Synechocystis 6714 mutant, loxII A , resistant to the phenol-type herbicide ioxynil was isolated and characterized. The mutation found in the psbA gene (encoding the D1 photosystem II protein) is at the same codon 266 as for the first ioxynil-resistant mutant IoxI A previously selected [G. Ajlani. I. Meyer, C. Vernotte. and C. Astier, FEBS Lett. 246, 207-210 (1989)]. In IoxII A , the change of Asn 266 to Asp gives a 3 × resistance, whereas in IoxI A , the change of the same amino acid to Thr gives a 10 × resistance. The effect of these different amino acid substitutions on the ioxynil resistance phenotype has allowed us to construct molecular models and calculate the hydrogen-bonding energies between the hydroxyl group of ioxynil and the respective amino acids at position 266

Time-resolved fluorescence of photosystem I in vivo : Global and target analysis

Photosystem I (PSI) is a multi-pigment-protein complex that co-operates with photosystem II (PSII) and uses light energy to transfer electrons from plastocyanin or cytochrome to ferredoxin and eventually to NADP+. Cyanobacterial BE mutant cells that lack PSII and light-harvesting phycobilisomes, provided us with the possibility to study the picosecond fluorescence kinetics of PSI in vivo and the results were analyzed using global and target analysis. The obtained components (5.4 ± 0.14 ps spectral equilibration and 27.8 ± 0.09 ps excitation trapping) are very similar to those found before for isolated PSI. The rate of energy transfer from red-shifted chlorophyll a (Chl a) molecules to bulk Chls a occurs with a rate constant of (7.4–10.4 ps)−1 whereas the reverse process occurs with a rate constant of (19.3–29.8 ps)−1 according to the target analysis, whereas trapping from bulk Chls a occurs with rate (16.8–25.0 ps)−1.</p