1997; Moya et al. 2001). The fast repetition rate (FRR) fluorescence technique uses a unique protocol to measure variable fluorescence. Instead of measuring fluorescence before and during a multiple turnover saturating light pulse, a sequence of rapidly fired sub-saturating flashlets

is used to completely reduce the QA pool. Because of the short duration of the flashlet sequence (about 280 μs), a fluorescence induction curve is measured within effectively a single PSII turnover event. From the kinetics of rise from F 0 to F m , Linsitinib the functional absorption cross section σPSII is calculated as well as the connectivity parameter p. The functional absorption cross section of PSII describes the efficiency of light utilisation of open PSII units and is equal to the product of the PSII efficiency and the optical cross section of PSII (Kolber and Falkowski 1993; Kolber et al. 1998). From preliminary studies we obtained evidence XMU-MP-1 concentration that the marine chlorophyte D. tertiolecta might possess some unique photoprotective features. Therefore, the current study presents observations on a unique, PF-dependent and rapid NPQ down-regulation upon light exposure in the marine chlorophyte D. tertiolecta, in order to get a better understanding of the photoprotective mechanisms activated upon exposure to high irradiances.

Materials and methods Culture conditions see more Continuous cultures of Dunaliella teriolecta (Butcher 1959) (CSIRO strain CS-175) were grown in a flat-faced 1.6 l glass vessel (approximately

5 cm light path) under constant aeration, and irradiance (100 μmol photons m−2 s−1, 400 W Philips high pressure HPIT E40 lamp) at 18°C. Cells were kept in a stable physiological state by means of continuous dilution (flow rate 64 ml/h, giving a dilution rate of ~0.95 day−1) with fresh F/2 enriched seawater medium (pH 8.2) at a cell density of 7.6 ± 1 × 105 cells/ml and a pH GBA3 of 8.7 ± 0.2 inside the culture vessel. A Coulter Counter (model ZM connected to a Coulter Multisizer, Beckman Coulter) was used to measure cell concentrations. Before measurement, cells were washed by gentle centrifugation and re-suspension of the pellet in fresh medium (pH 8.2) at a similar cell concentration as under growth conditions. Dark acclimation prior to measurement never exceeded 2 h. FRRF measurements Variable chlorophyll fluorescence was measured using a Fast Repetition Rate fluorometer (FRRF) (FastTracka-I, Chelsea Technology Group Ltd, UK). For a general description of a FRR fluorometer and FRRF theory see, e.g. Kolber and Falkowski (1993) and Kolber et al. (1998). A flashlet sequence (5 replicates, saturation flash length 1.1 μs and saturation flash period 2.8 μs) was applied every 13 s. Although the intensity of the individual flashlets is sub-saturating due to their short interval, the overall photon flux (~30.000 μmol photons m−2 s−1) is highly saturating.