title: Parallel changes in non-photochemical quenching properties, photosynthesis and D1 levels at sudden, prolonged irradiance exposures in Ulva fasciata Delile.
abstract: The photosynthetic response to a sudden and prolonged high irradiance exposure and following recovery at low irradiance were studied with the aim of investigating the ability to withstand and adapt to high irradiance without prior high light adaptation. When thalli of Ulva fasciata, accustomed to a low irradiance (80 micromol photons m(-2) s(-1)), were exposed to a high irradiance (1500 micromol photons m(-2) s(-1)), the D1 protein was rapidly degraded, reaching a steady-state level after 110 min. This was followed by a fast recovery when thalli were transferred to dim light. The overall ability of non-photochemical quenching of chlorophyll fluorescence decreased and levelled off at a sudden and prolonged exposure to high irradiance and followed the same trend as the D1 level with a fast recovery in dim light. Ulva had intrinsic means to acclimate rapidly to high irradiance, when non-photochemical quenching did not operate properly, by maintaining a smaller fraction of high light tolerant PSII assemblages and by maintaining a high non-photochemical quenching capacity of chlorophyll fluorescence in relation to the variable fluorescence. The overall absorption of light (400-700 nm) remained high during the period of high irradiance exposure. When Ulva were deprived of nutrients in the form of PES media the ability of non-photochemical quenching decreased at photoinhibitory conditions. The possible causes for the responses at prolonged irradiance and the mechanisms for the decrease of non-photochemical quenching are discussed, with implications for field measurements.
authors.affiliation: Botany Department, Stockholm University, Lilla Frescativägen 5, SE-106 91, Stockholm, Sweden. carr@botan.su.se
authors.forename: Herman
authors.initials: H
authors.lastname: Carr
authors.forename: Mats
authors.initials: M
authors.lastname: Björk
mesh_terms: D007700:Kinetics; D010100:Oxygen / Q000378:metabolism; D010777:Photochemistry; D017785:Photons; D010788:Photosynthesis / Q000528:radiation effects*; D045332:Photosystem II Protein Complex / Q000528:radiation effects; D013636:Tanzania; D013997:Time Factors; D044445:Ulva / Q000528:radiation effects*
chemical_list: D045332:Photosystem II Protein Complex; D010100:Oxygen