PARENT SESSION
Posters P1B Photo-oxidative stress, photoinhibition. Abstracts (394-443)

Repair of photodamaged Photosystem II is inhibited by NaCl at transcription and translation of PsbA genes in Synechocystis. Sachio MIYAIRI^{*,1, 2}, Suleyman ALLAKHVERDIEV^{1, 3}, Yoshitaka NISHIYAMA^{1, 4}, Norio MURATA¹, ¹ National Institute for Basic Biology, Japan² National Institute of Advanced Industrial Science and Technology, Japan³ Institute of Basic Biological Problems RAS, Russia⁴ Ehime University, Japan

ABSTRACT- Light stress and salt stress are major environmental factors that limit the efficiency of photosynthesis. Here we report the effects of light stress and salt stress, alone and in combination on the activity of photosystem II (PSII). We observed that neither strong light nor salt stress in darkness impaired the activity of PSII, but combination of light and salt stress appeared to inactivate PSII in the cyanobacterium Synechocystis sp. PCC 6803 very rapidly as a consequence of their synergistic effects. The activity of PSII that had been lost during incubation under very strong light was restored when cells were transferred to normal weak light. However, salt stress prevented such recovery, as did lincomycin, an inhibitor of protein synthesis. These results suggested that salt stress might inhibit the recovery of PSII from light-induced damage. Radioactive labeling of cells revealed that salt stress inhibited the synthesis of proteins de novo. Northern- and western-blotting analyses further demonstrated that salt stress inhibited two steps in expression of psbA genes, which encode the precursor to the D1 protein (pre-D1), namely transcription of these genes and translation of their transcripts.

KEY WORDS: salt and light stresses, Synechocystis, D1 protein, photosystem II