Energy dissipation pathways in Photosystem 2 of the diatom, Phaeodactylum tricornutum, under high-light conditions

Abstract

To prevent photooxidative damage under supraoptimal light, photosynthetic organisms evolved mechanisms to thermally dissipate excess absorbed energy, known as non-photochemical quenching (NPQ). Here we quantify NPQ-induced alterations in light-harvesting processes and photochemical reactions in Photosystem 2 (PS2) in the pennate diatom Phaeodactylum tricornutum. Using a combination of picosecond lifetime analysis and variable fluorescence technique, we examined the dynamics of NPQ activation upon transition from dark to high light. Our analysis revealed that NPQ activation starts with a 2-3-fold increase in the rate constant of non-radiative charge recombination in the reaction center (RC); however, this increase is compensated with a proportional increase in the rate constant of back reactions. The resulting alterations in photochemical processes in PS2 RC do not contribute directly to quenching of antenna excitons by the RC, but favor non-radiative dissipation pathways within the RC, reducing the yields of spin conversion of the RC chlorophyll to the triplet state. The NPQ-induced changes in the RC are followed by a gradual ~ 2.5-fold increase in the yields of thermal dissipation in light-harvesting complexes. Our data suggest that thermal dissipation in light-harvesting complexes is the major sink for NPQ; RCs are not directly involved in the NPQ process, but could contribute to photoprotection via reduction in the probability of (3)Chl formation.

Photosynthetic physiology and biomass partitioning in the model diatom Phaeodactylum tricornutum grown in a sinusoidal light regime

“…4D). NPQ reduces the effective transfer of light energy to the reaction center of PSII and it has been previously shown to negatively correlate with σ PSII in Phaeodactylum [60,61]. The maximal NPQ values in the ex situ RLCs were higher than those estimated by our in situ methods (Fig.…”

Light availability rather than Fe controls the magnitude of massive phytoplankton bloom in the Amundsen Sea polynyas, Antarctica

“…In order to eliminate the effect of photoinhibition only night time values of F v / F m and fluorescence lifetimes were used. Solid gray line (with 0% mark) is the theoretical dependence between the fluorescence lifetime and F v / F m given the following dependence: F v / F m = ( τ m ‐ τ )/ τ m , where τ m is estimated to be 1.5 ns (Kuzminov and Gorbunov ), and τ varies from 0.5 ns to 1.5 ns. Solid light gray line (with 10–40% marks) is the modeled dependence between F v / F m and τ , when 10–40% of the antenna are detached from the photosynthetic reaction center and have fluorescence lifetime of 4 ns.…”

“…Under optimal conditions, when all the reaction centers are active and open, the fluorescence lifetimes are minimal (∼ 0.5–0.6 ns). When the reaction centers are closed (i.e., photochemistry is nil), the lifetimes increase to 1.5–1.8 ns (Kuzminov and Gorbunov ). Nutrient stress also leads to an increase in fluorescence lifetimes due to an increase in the fraction of inactive reaction centers and the presence of uncoupled light‐harvesting antennae (Vassiliev et al ; Behrenfeld et al ; Schrader et al ; Lin et al ).…”

“…Picosecond fluorescence decay kinetics were measured using a custom‐built lifetime fluorometer, called PicoLiF, as described in Kuzminov and Gorbunov () and Lin et al (). Both mini‐FIRe and PicoLiF instruments are extremely sensitive and can accurately record fluorescence kinetics in ultra‐low chlorophyll concentrations (down to 0.01 mg m −3 ).…”

Photosynthetic energy conversion efficiency in the West Antarctic Peninsula

“…To cope, iron‐limited phytoplankton increase rapid nonphotochemical quenching (NPQ) components (Petrou et al 2011; Alderkamp et al 2013). NPQ represents a suite of photoprotective mechanisms activated at high light, effectively increasing Φ T and simultaneously decreasing σ PSII (Goss and Lepetit 2015; Kuzminov and Gorbunov 2016; Buck et al 2019). Further work is needed to rapidly assess the occurrence and function of these physiological responses to iron limitation in natural assemblages (Behrenfeld and Milligan 2013).…”