Cyclic electron transfer in photosystem II in the marine diatom Phaeodactylum tricornutum

Abstract

In Phaeodactylum tricornutum Photosystem II is unusually resistant to damage by exposure to high light intensities. Not only is the capacity to dissipate excess excitations in the antenna much larger and induced more rapidly than in other organisms, but in addition an electron transfer cycle in the reaction center appears to prevent oxidative damage when secondary electron transport cannot keep up with the rate of charge separations. Such cyclic electron transfer had been inferred from oxygen measurements suggesting that some of its intermediates can be reduced in the dark and can subsequently compete with water as an electron donor to Photosystem II upon illumination. Here, the proposed activation of cyclic electron transfer by illumination is confirmed and shown to require only a second. On the other hand the dark reduction of its intermediates, specifically of tyrosine Y(D), the only Photosystem II component known to compete with water oxidation, is ruled out. It appears that the cyclic electron transfer pathway can be fully opened by reduction of the plastoquinone pool in the dark. Oxygen evolution reappears after partial oxidation of the pool by Photosystem I, but the pool itself is not involved in cyclic electron transfer.

Photosynthesis and net primary productivity in three Antarctic diatoms: possible significance for their distribution in the Antarctic marine ecosystem

“…Although no direct measurements of cyclic electron transport of PSII were made in this study, it seems highly likely that the difference in the shape of the light response curves and E K values based on fluorescence and oxygen measurements can be attributed to the non-oxygen-consuming process of cyclic electron transport around PSII (Prasil et al 1996, Lavaud et al 2002. The advantage to cyclic electron transport is that it can be switched on faster than heat dissipation via non-photochemical quenching (Onno Feikema et al 2006) and allows the cell to maintain maximum photosynthetic capacity while keeping energy-dependent quenching minimal (Lavaud 2007).…”

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

“…Changes in cellular energy allocation, controlled in part by endogenous circadian rhythms, could also have affected the conversion factor K c /n PSII , by rerouting NADPH and ATP generated by the photosynthetic light reaction to processes other than carbon fixation, thus increasing K c /n PSII . Processes decoupling ETR RCII from carbon fixation include nutrient assimilation (Laws, 1991), carbon concentrating mechanisms (Giordano et al, 2005), photorespiration (Foyer et al, 2009), and malate formation (Halsey and Jones, 2015). Pseudo-cyclic electron transport through the Mehler-ascorbate peroxidase pathway also has the ability to increase the conversion factor K c /n PSII by allowing ETR RCII to increase without affecting carbon fixation (Miyake and Asada, 2003;Niyogi, 2000).…”

“…Marine phytoplankton account for ∼ 50 % of global carbon fixation (Field et al, 1998) and play a key role in Earth's biogeochemical cycles. Understanding the spatial and temporal patterns in marine primary productivity and its response to environmental variability is thus a central oceanographic research question.…”

High Light Acclimation in the Secondary Plastids Containing Diatom Phaeodactylum tricornutum is Triggered by the Redox State of the Plastoquinone Pool

“…In diatoms, the involvement of photoreceptors in photosynthetic regulatory processes has been revealed recently (Depauw et al, 2012), while redox regulation via thioredoxins seems to be of minor importance for the regulation of the Calvin cycle (Kroth et al, 2008), even if thioredoxins may control the activity of carboanhydrases in the pyrenoid (Kikutani et al, 2012). The redox state of the PQ pool is of crucial importance in several photosynthetic regulatory processes, such as the PSII electron cycle (Onno Feikema et al, 2006;Lavaud et al, 2007), nonphotochemical fluorescence quenching (NPQ; Lavaud, 2007;Lavaud et al, 2007), and chlororespiration (Caron et al, 1987;Dijkman and Kroon, 2002;Grouneva et al, 2009). The dynamics of the PQ pool redox state as a function of light intensity differ between diatom species and between diatoms and land plants (Ruban et al, 2004;Lavaud, 2007;Materna et al, 2009).…”