Abstract
Glycinebetaine (betaine) is one of the compatible solutes and is accumulated in various organisms in response to stress conditions. Synechococcus sp. PCC7942 that had been transformed with the codA gene for choline oxidase retained the ability to synthesize betaine in the presence of choline and enhanced tolerance against cold and salt stress. We have already demonstrated that betaine enhanced the repair of photosystem II (PSII) during photoinhibition with salt stress although neither salt stress nor betaine affected the photodamage to PSII. A further investigation of the effects of betaine on photoinhibition of PSII in Synechococcus cells showed that salt stress inhibited the degradation and synthesis de novo of D1 and caused the slow repair of PSII. Betaine alleviated both kinds of inhibition, resulting in accelerated repair of PSII. We will also discuss about the effect of salt stress and betaine on transcription of the psbA gene.
