Inactivation by gene disruption of 2‐cysteine‐peroxiredoxin in Synechocystis sp. PCC 6803 leads to increased stress sensitivity

2‐Cysteine‐peroxiredoxins (2‐CP) constitute a ubiquitous group of enzymes which reduce toxic alkyl hydroperoxides. In higher plants it was shown that the nuclear encoded 2‐CPs are posttranslationally imported into the chloroplasts, the site of most active oxidative metabolism in plants (Baier and Dietz 1997, Plant J. 12; 179‐190). The genome of the bluegreen alga Synechocystis (EMBL acc. # D64000) encodes a 2‐CP which shares 60% homology to higher plant 2‐CPs on the gene level and about 70% on the level of the mature protein. In order to elucidate the physiological significance of 2‐CPs for photosynthetic organisms, the 2‐CP gene was mutated in Synechocystis sp. PCC 6803 by insertion of a kanamycin gene cartridge. Following complete segregation mutant lines were analyzed for growth and photosynthetic parameters. The mutants revealed decreased growth rates as compared to the wild type. Growth inhibition was relieved after lowering the concentration of Fe or trace elements in the growth medium. Chlorophyll a fluorescence transients as induced by saturating light pulses were used as indicator for the state of photosynthesis. The effective quantum yield decreased at lower light intensities in the mutants as compared to the wild type Synechocystis . Simultaneously, electron transport rates saturated at lower light intensities in the mutants. These data provide the first evidence that 2‐CPs play a pivotal protective role in photosynthesis.