The name constitutional NPQ (photophysical learn more decay) suggests that this does not vary significantly

with different irradiances. This is indeed observed in a number of higher plant studies (Ahn et al. 2009; Guadagno et al. 2010). These latter studies also expanded the analysis of the portioning of quantum efficiencies to a better description of the importance of qE, qI and qT in ΦNPQ. Our data clearly show that in the unicellular alga D. tertiolecta, Φf,D varies with irradiance. In the block high light treatment Φf,D is higher in the light than in the darkness, but in the light the variability in Φf,D is limited. However, when the same procedure is followed for the stepwise increase in irradiance Φf,D shows large oscillations, in contrast to the situation described in higher plants. Unfortunately, we were able to find only one study in which energy apportioning was studied in algae. The unicellular microalgae Chlamydomonas raudensis showed variability

in constitutive (or non-regulated) NPQ, which increased as a function of the growth light intensity (Szyszka et al. 2007). Constitutive NPQ also showed variations due to exposure to different growth temperature conditions with variations that do not extend approximately 5% in a higher plant (Hendrickson et al. 2004). Neither of these studies employed the high temporal measurement frequencies that isometheptene we used, making it difficult to compare our studies to the literature. HDAC inhibitor drugs In this study, it can be clearly seen

that Φf,D responds rapidly to various PF conditions in D. tertiolecta. Nevertheless, as Φf,D increases when cells are exposed to sub-saturating PF during a dark–light transition, while other NPQ parameters decrease, it seems reasonable to suggest that Φf,D acts as an important short-term safety valve and can operate independently from other NPQ mechanisms. Further, it seems possible that similar responses operate when cells are exposed to high PF, but have not been detected in this study as response times might be so rapid that they occur between measurements conducted by the measurement protocol (13 s). The rapid, and xanthophyll cycle independent, fraction of qE can act as an efficient photoprotective mechanism in algae and might be attributed to PSII reaction centre quenching, whether this is due to charge recombination, direct P680+ quenching, spill-over or conformational changes in the PSII core subunits (Olaiza et al. 1994; Doege et al. 2000; Eisenstadt et al. 2008; Ivanov et al. 2008; Raszewski and Renger 2008). As constitutive thermal dissipation (Φf,D) originates in the PSII core (Ivanov et al. 2008), it can be concluded that D. tertiolecta is capable of rapidly changing PSII reaction core properties to avoid photodamage.