Photoacclimation in Dunaliella tertiolecta reveals a unique NPQ pattern upon exposure to irradiance

Abstract

Highly time-resolved photoacclimation patterns of the chlorophyte microalga Dunaliella tertiolecta during exposure to an off–on–off (block) light pattern of saturating photon flux, and to a regime of consecutive increasing light intensities are presented. Non-photochemical quenching (NPQ) mechanisms unexpectedly responded with an initial decrease during dark–light transitions. NPQ values started to rise after light exposure of approximately 4 min. State-transitions, measured as a change of PSII:PSI fluorescence emission at 77 K, did not contribute to early NPQ oscillations. Addition of the uncoupler CCCP, however, caused a rapid increase in fluorescence and showed the significance of qE for NPQ. Partitioning of the quantum efficiencies showed that constitutive NPQ was (a) higher than qE-driven NPQ and (b) responded to light treatment within seconds, suggesting an active role of constitutive NPQ in variable energy dissipation, although it is thought to contribute statically to NPQ. The PSII connectivity parameter p correlated well with F′, Fm′ and NPQ during the early phase of the dark–light transients in sub-saturating light, suggesting a plastic energy distribution pattern within energetically connected PSII centres. In consecutive increasing photon flux experiments, correlations were weaker during the second light increment. Changes in connectivity can present an early photoresponse that are reflected in fluorescence signals and NPQ and might be responsive to the short-term acclimation state, and/or to the actinic photon flux.

Photophysiological responses of Southern Ocean phytoplankton to changes in CO2 concentrations: Short-term versus acclimation effects

“…We suggest that higher rETRs were enabled in this species because of higher fixation rates by RubisCO at elevated pCO 2 . A similar conclusion was drawn by Ihnken et al (2011aIhnken et al ( , 2011b, who found enhanced rETRs in high CO 2 -acclimated cells of the temperate diatom C. muelleri. Interestingly, such a response was not observed in our tested Chaetoceros species that manifested signs of dynamic photoinhibition independent of the acclimation pCO 2 .…”

“…6). Such changes in connectivity were also found in the temperate chlorophyte Dunaliella tertiolecta in response to darklight transitions (Ihnken et al, 2011a(Ihnken et al, , 2011b. In our experiments, p′ values determined at the end of the light phase were below 0.1 in all tested species (Fig.…”

“…Kranz et al (2010) observed Mehler activity in the cyanobacterium Trichdesmium, which was acclimated to low pCO 2 combined with high light, but this process was absent under high pCO 2 . In the temperate diatom Chaetoceros muelleri, increasing pCO 2 was found to enhance relative electron transport rates (rETRs) under saturating light, suggesting that higher rETRs were enabled because of elevated CO 2 fixation rates by RubisCO (Ihnken et al, 2011a(Ihnken et al, , 2011b. McCarthy et al (2012) also observed higher carboxylation rates with increasing pCO 2 in two temperate diatom strains of Thalassiosira pseudonana.…”

“…Next to the adjustment of cellular pigment composition and concentration Van Leuwe et al, 2005), the photoacclimation strategy of polar phytoplankton is to adjust photosystem II (PSII) reaction centers through changing the size of the effective absorption cross-section (σ PSII ) rather than the number of PSII reaction centers per cell Robinson et al, 1997). Phytoplankton can also alter the PSII connectivity (p) allowing the redistribution of excitons from closed to open PSII providing a more or less efficient use of light (Ihnken et al, 2011b). Regarding the impact of pCO 2 on photophysiology, Spalding et al (1984) reported an increase in σ PSII in Chlamydomonas reinhardtii when grown at 5% CO 2 .…”

Light acclimation and pH perturbations affect photosynthetic performance in Chlorella mass culture

“…Samples were dark-acclimated only very briefly (≤2 s), which will oxidize primary electron acceptors in PSII (Q A − ), but not secondary electron acceptors or the PQ pool (Strasser et al 1995), or relax photoprotective NPQ. Although the rapid phase of energy dependent quenching (q E ) might relax due to a dissipation of the ΔpH-gradient within seconds, xanthophyll cycle-mediated q E requires minutes, as do statetransitions (Müller et al 2001, Ihnken et al 2011a. Residual NPQ in illuminated samples can explain the obvious difference between initial samples, which were dark-acclimated overnight, and samples taken at low PF.…”