The fluorescence yield of the trimeric fucoxanthin–chlorophyll–protein FCPa in the diatom Cyclotella meneghiniana is dependent on the amount of bound diatoxanthin

Abstract

The fluorescence yield of isolated fucoxanthin chlorophyll proteins, serving as light harvesting proteins in diatoms, was compared to the amount of diatoxanthin bound. Diatoxanthin was earlier shown to be involved in the xanthophyll cycle in diatoms as a functional analogue of zeaxanthin in higher plants. By growing cells under different light conditions, the amount of diatoxanthin in both the trimeric FCPa as well as the oligomeric FCPb of the diatom Cyclotella meneghiniana was increased. In the trimeric FCPa, the fluorescence yield decreased with increasing diatoxanthin content, whereas in the oligomeric FCPb fluorescence was generally lower, albeit constant. No pH dependence of fluorescence yield could be demonstrated except for artificially aggregated FCPa. Thus, diatoxanthin is able to quench fluorescence in FCPa, but the yield is also influenced by pH when the protein becomes aggregated.

Evidence for the Existence of One Antenna-Associated, Lipid-Dissolved and Two Protein-Bound Pools of Diadinoxanthin Cycle Pigments in Diatoms

“…These pigments are visible in the fluorescence excitation spectra, which means that they act as accessory pigments in the peripheral FCP. FCPb complexes also contain protein-bound Ddx pigments, but in a much lower amount compared with FCPa (Gundermann and Bü chel, 2008;Gildenhoff et al, 2010). Importantly, in P. tricornutum, protein-bound Ddx cycle pigments are also present in the FCP (data not shown).…”

“…Despite our increasing knowledge about the composition of the diatom antenna complexes, it is not exactly clear at present which Lhc proteins bind the pigments of the Ddx cycle. Evidence for the existence of a special Ddxbinding protein in diatoms was found for C. meneghiniana, where the FCPa complex is enriched in these pigments, whereas the FCPb complex seems to bind only very small amounts of Ddx (Gundermann and Bü chel, 2008). In addition, Guglielmi et al (2005) reported the existence of special Ddx-binding FCPs, whose identity remained unclear.…”

The Xanthophyll Cycle in Aquatic Phototrophs and Its Role in the Mitigation of Photoinhibition and Photodynamic Damage

“…These two types of responses, regulative and acclimative, are not mutually exclusive . For instance, long-term acclimation to a prolonged light regime (low or high intensity, or intermittent light) modifies the amount of pigments involved in the xanthophyll cycle, leading to a modulation of the high light response via the kinetics and amplitude of NPQ (Dimier et al, 2009b;Gundermann & Büchel, 2008;Lavaud et al, 2003;van de Poll et al, 2007). …”

Macro-organization and structural flexibility of the photosynthetic pigment system in diatoms

“…In diatoms, the correlation between conformational changes of FCP complexes and the quenching of fluorescence is far less understood. It has been estimated that in C. meneghiniana the FCPa and FCPb complexes exhibit significant fluorescence quenching which was dependent on pH but only if the complexes were aggregated in vitro (Gundermann and Büchel, 2008). Thus, the relationship of fluorescence quenching and the state of aggregation of the FCP in vivo still remains to be clarified.…”

“…There are studies available on isolated FCP complexes which exhibit markedly different fluorescence yield in different aggregation states (e.g. Gundermann et al 2008), however, the physiological role of aggregation of FCP is not elucidated yet. Miloslavina et al (2009) provided the first evidence that under NPQ conditions part of the FCP complexes detaches from PSII reaction center and becomes aggregated and the mechanism of aggregation is similar to that of observed in vitro.…”