title: Rapid interchange between two distinct forms of cyanobacterial photosystem II reaction-center protein D1 in response to photoinhibition.
abstract: We have studied photoinhibition of photosynthesis in the cyanobacterium Synechococcus sp. PCC 7942, which possesses two distinct forms of the photosystem II reaction-center protein D1 (D1:1 and D1:2). We report here that when cells adapted to a growth irradiance of 50 mumol.m-2.s-1 are exposed to an irradiance of 500 mumol.m-2.s-1, the normally predominant D1 form (D1:1) is rapidly replaced with the alternative D1:2. This interchange is not only complete within the first hour of photoinhibition but is also fully reversible once cells are returned to 50 mumol.m-2 x s-1. By using a mutant that synthesizes only D1:1, we show that the failure to replace D1:1 with D1:2 during photoinhibition results in severe loss of photosynthetic activity as well as a diminished capacity to recover after the stress period. We believe that this interchange between D1 forms may constitute an active component in a protection mechanism unique among photosynthetic organisms that enables cyanobacteria to effectively cope with and recover from photoinhibition.
authors.affiliation: Department of Plant Physiology, University of Umeå, Sweden.
authors.forename: A K
authors.initials: AK
authors.lastname: Clarke
authors.forename: A
authors.initials: A
authors.lastname: Soitamo
authors.forename: P
authors.initials: P
authors.lastname: Gustafsson
authors.forename: G
authors.initials: G
authors.lastname: Oquist
mesh_terms: D000458:Cyanobacteria / Q000235:genetics / Q000378:metabolism*; D005798:Genes, Bacterial; D015151:Immunoblotting; D007700:Kinetics; D008027:Light; D016296:Mutagenesis; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins