The trade‐off between the light‐harvesting and photoprotective functions of fucoxanthin‐chlorophyll proteins dominates light acclimation in Emiliania huxleyi (clone CCMP 1516)

Abstract

SummaryMechanistic understanding of the costs and benefits of photoacclimation requires knowledge of how photophysiology is affected by changes in the molecular structure of the chloroplast.We tested the hypothesis that changes in the light dependencies of photosynthesis, nonphotochemical quenching and PSII photoinactivation arises from changes in the abundances of chloroplast proteins in Emiliania huxleyi strain CCMP 1516 grown at 30 (Low Light; LL) and 1000 (High Light; HL) lmol photons m À2 s À1 photon flux densities. Carbon-specific light-saturated gross photosynthesis rates were not significantly different between cells acclimated to LL and HL. Acclimation to LL benefited cells by increasing biomass-specific light absorption and gross photosynthesis rates under low light, whereas acclimation to HL benefited cells by reducing the rate of photoinactivation of PSII under high light. Differences in the relative abundances of proteins assigned to light-harvesting (Lhcf), photoprotection (LI818-like), and the photosystem II (PSII) core complex accompanied differences in photophysiology: specifically, Lhcf:PSII was greater under LL, whereas LI818:PSII was greater in HL.Thus, photoacclimation in E. huxleyi involved a trade-off amongst the characteristics of light absorption and photoprotection, which could be attributed to changes in the abundance and composition of proteins in the light-harvesting antenna of PSII.

Resistance of Arctic phytoplankton to ocean acidification and enhanced irradiance

“…Furthermore, the assemblage was dominated by diatoms, which are known to possess highly efficient photo-protective machinery (Lavaud et al 2004). Our FRRF measurements indeed revealed a high capacity for energy dissipation via NPQ (Table 4), even when compared to relatively high values previously measured in diatom-dominated Arctic phytoplankton assemblages as well as individual diatom and haptophyte strains (McKew et al 2013;Hoppe et al 2015;Schuback et al 2017). Moreover, relatively high temperatures occurring in the incubators may have helped to prevent high-light stress by increasing the turnover rate of carbon fixation relative to electron transport, thereby allowing the Calvin cycle to be a more efficient sink for light energy (Mock and Hoch 2005;Goldman et al 2015).…”

“…Non-photochemical quenching (NPQ) for each light level was estimated as the normalized Stern-Volmer quenching coefficient, McKew et al 2013). NPQ NSV represents the ratio of total non-photochemical energy dissipation in the light-regulated state to the rate constant of photochemistry.…”

Importance of deep mixing and silicic acid in regulating phytoplankton biomass and community in the iron-limited Antarctic Polar Front region in summer

“…0.65 under optimal nutrient replete conditions (Kolber and Falkowski, 1993), low mean F v =F m ð o 0:40Þ values observed across the north and south regions of the APF could be attributed to iron limitation. Low mean values of 1=τ Qa ð o0:3 m s À 1 Þ across the APF suggest that there was a large proportion of reduced plastoquinone pool (McKew et al, 2013), which could have resulted from a large proportion of reduced RCII. Laboratory and ship-board iron fertilisation experiments have reported an increase in F v =F m to 4 0:5 and 1=τ Qa 4 0:3 m s À 1 in response to iron addition (Greene et al, 1992;Kolber et al, 1994;Moore et al, 2007).…”

“…Fluorescence transients were then fitted to the biophysical model of Kolber et al (1998) (Olaizola et al, 1994), which does not resolve the important differences between downregulation of excitation energy transfer in high light-and low light-adapted cells (McKew et al, 2013). NPQ NSV resolves these differences and is appropriate for our data set.…”

Diurnal variation in the coupling of photosynthetic electron transport and carbon fixation in iron-limited phytoplankton in the NE subarctic Pacific

“…We used values of τ , estimated for the dark-regulated state at each TP, to derive estimates of the rate of Q A reoxidation (1/τ ; ms −1 ). Non-photochemical quenching (NPQ) at each light level was estimated as the so-called normalized SternVolmer quenching coefficient, McKew et al, 2013). This alternative approach to the more common estimate of NPQ ((F m − F m )/F m ; Bilger and Björkman, 1990) represents the ratio of total nonphotochemical energy dissipation in the light-regulated state to the rate constant of photochemistry (McKew et al, 2013).…”