title: Light acclimation in the lycophyte Selaginella martensii depends on changes in the amount of photosystems and on the flexibility of the light-harvesting complex II antenna association with both photosystems.
abstract: Vascular plants have evolved a long-term light acclimation strategy primarily relying on the regulation of the relative amounts of light-harvesting complex II (LHCII) and of the two photosystems, photosystem I (PSI) and photosystem II (PSII). We investigated whether such a model is also valid in Selaginella martensii, a species belonging to the early diverging group of lycophytes. Selaginella martensii plants were acclimated to three natural light regimes (extremely low light (L), medium light (M) and full sunlight (H)) and thylakoid organization was characterized combining ultrastructural, biochemical and functional methods. From L to H plants, thylakoid architecture was rearranged from (pseudo)lamellar to predominantly granal, the PSII : PSI ratio changed in favour of PSI, and the photochemical capacity increased. However, regulation of light harvesting did not occur through variations in the amount of free LHCII, but rather resulted from the flexibility of the association of free LHCII with PSII and PSI. In lycophytes, the free interspersed LHCII serves a fixed proportion of reaction centres, either PSII or PSI, and the regulation of PSI-LHCII(-PSII) megacomplexes is an integral part of long-term acclimation. Free LHCII ensures photoprotection of PSII, allows regulated use of PSI as an energy quencher, and can also quench endangered PSI.
authors.affiliation: Department of Life Sciences and Biotechnology, University of Ferrara, C.so Ercole I d'Este 32, 44121, Ferrara, Italy.
authors.forename: Lorenzo
authors.identifier: 0000-0002-5694-2078
authors.initials: L
authors.lastname: Ferroni
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014, Turku, Finland.
authors.forename: Marjaana
authors.initials: M
authors.lastname: Suorsa
authors.affiliation: Department of Biochemistry, Molecular Plant Biology, University of Turku, FI-20014, Turku, Finland.
authors.forename: Eva-Mari
authors.initials: EM
authors.lastname: Aro
authors.affiliation: Department of Life Sciences and Biotechnology, University of Ferrara, C.so Ercole I d'Este 32, 44121, Ferrara, Italy.
authors.forename: Costanza
authors.initials: C
authors.lastname: Baldisserotto
authors.affiliation: Department of Life Sciences and Biotechnology, University of Ferrara, C.so Ercole I d'Este 32, 44121, Ferrara, Italy.
authors.forename: Simonetta
authors.initials: S
authors.lastname: Pancaldi
mesh_terms: D000064:Acclimatization / Q000528:radiation effects*; D003624:Darkness; D004579:Electron Transport / Q000528:radiation effects; D007700:Kinetics; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D010084:Oxidation-Reduction; D010788:Photosynthesis / Q000528:radiation effects; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D011485:Protein Binding / Q000528:radiation effects; D032503:Selaginellaceae / Q000502:physiology* / Q000528:radiation effects*; D012995:Solubility; D013696:Temperature; D020524:Thylakoids / Q000378:metabolism / Q000528:radiation effects
chemical_list: D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex
keywords: Selaginella martensii; chlorophyll fluorescence; light acclimation; light-harvesting complex; lycophytes; native gel electrophoresis; photosystem; thylakoid membrane