Ultrafast fluorescence study on the location and mechanism of non-photochemical quenching in diatoms

Abstract

The diatom algae, responsible for at least a quarter of the global photosynthetic carbon assimilation in the oceans, are capable of switching on rapid and efficient photoprotection, which helps them cope with the large fluctuations of light intensity in the moving waters. The enhanced dissipation of excess excitation energy becomes visible as non-photochemical quenching (NPQ) of chlorophyll a fluorescence. Intact cells of the diatoms Cyclotella meneghiniana and Phaeodactylum tricornutum, which show different NPQ induction kinetics under high light illumination, were investigated by picosecond time-resolved fluorescence under dark and NPQ-inducing high light conditions. The fluorescence kinetics revealed that there are two independent sites responsible for NPQ. The first quenching site is located in an FCP antenna system that is functionally detached from both photosystems, while the second quenching site is located in the PSII-attached antenna. Notwithstanding their different npq induction and reversal kinetics, both diatoms showed identical NPQ via both mechanisms in the steady-state. Their fluorescence decays in the dark-adapted states were different, however. A detailed quenching model is proposed for NPQ in diatoms.

Functional heterogeneity of the fucoxanthins and fucoxanthin-chlorophyll proteins in diatom cells revealed by their electrochromic response and fluorescence and linear dichroism spectra

“…In addition, the FCP composition of the antenna varied if the algae were grown under LL or HL conditions [31] . Heterogeneity of FCPs can also be seen in the ultrafast fluorescence decay kinetics [32], which showed that two different pools of FCPs are responsible for the generation of steady-state non-photochemical fluorescence quenching (NPQ) in the diatoms P. tricornutum and C. meneghiniana. One pool of FCPs, detached from the photosystems, forms a fluorescence-quenching site, whereas the second quenching site consists of FCPs that remain in contact with the PSII core complex [32].…”

Relaxation of the non-photochemical chlorophyll fluorescence quenching in diatoms: kinetics, components and mechanisms

“…qNf could be related to a fast conformational change occurring within the thylakoid membranes at the start of the relaxation process. The different (very fast in their creation) qN components could be localized on PSII attached or detached LHCs [58]. The former would be related to the qN enhancing mechanism(s), whereas qNs could be heterogeneous from the mechanistic point of view and related to photoinhibition and/or partial dissipation of the pH gradient.…”

The spectral sensitivity of phytoplankton communities to ultraviolet radiation‐induced photoinhibition differs among clear and humic temperate lakes

“…Nonphotochemical quenching (NPQ) is an additional mechanism that decreases the variable fluorescence of PSII, and all water samples were dark-adapted for 30 min prior to PAM analysis in order to control for this. However, there is emerging evidence suggesting that, in certain diatom species, low levels of PAR are required for complete relaxation of NPQ (Grouneva et al 2008Miloslavina et al 2009). Given that these diatom species were not present in any of the phytoplankton communities we examined, and that diatoms were a very minor component of the phytoplankton in the two lakes that exhibited the greatest losses of F V : F M under irradiance (Brandy and Fawn lakes), it seems unlikely that residual NPQ appreciably affected our measurement of F V : F M .…”