Mobilization of Photosystem II Induced by Intense Red Light in the Cyanobacterium Synechococcus sp PCC7942

Mary Sarcina ¹, Nikolaos Bouzovitis ¹, and Conrad W. Mullineaux ¹^*

¹ School of Biological Sciences, Queen Mary, University of London, London E1 4NS, United Kingdom

^* To whom correspondence should be addressed. E-mail: c.mullineaux{at}qmul.ac.uk.

We use confocal fluorescence microscopy and fluorescence recoveryafter photobleaching to show that a specific light signal controlsthe diffusion of a protein complex in thylakoid membranes ofthe cyanobacterium Synechococcus sp PCC7942 in vivo. In lowlight, photosystem II appears completely immobile in the membrane.However, exposure to intense red light triggers rapid diffusionof up to $~$ 50% of photosystem II reaction centers. Particularlyintense or prolonged red light exposure also leads to the redistributionof photosystem II to specific zones within the thylakoid membranes.The mobilization does not result from photodamage but is triggeredby a specific red light signal. We show that mobilization ofphotosystem II is required for the rapid initiation of recoveryfrom photoinhibition. Thus, intense red light triggers a switchfrom a static to a dynamic configuration of thylakoid membraneprotein complexes, and this facilitates the rapid turnover andrepair of the complexes. The localized concentrations of photosystemII seen after red light treatment may correspond to specificzones where the repair cycle is active.