Photo‐reducible plastoquinone pools in chloroplasts of Tradescentia plants acclimated to high and low light

Abstract

In photosynthetic systems of oxygenic type, plastoquinone (PQ) molecules are reduced by photosystem II (PSII). The turnover of PQ determines the rate of PSII operation. PQ molecules are present in surplus with respect to PSII. In this work, using the pulse amplitude modulation‐fluorometry technique, we quantified photo‐reducible PQ pools in chloroplasts of two contrasting ecotypes of Tradescantia, acclimated either to low light (~ 100 μmol photons·m−2·s−1, LL) or to high light (~ 1000 μmol photons·m−2·s−1, HL). The LL‐grown plants are characterized by higher capacity of rapidly reducible PQ pool ([PQ]0/[PSII] ≈ 8) as compared to HL‐grown plants of both species ([PQ]0/[PSII] ≈ 4). The elevated content of PQ in LL plants favours photosynthetic electron flow at low‐solar irradiance.

Structure of Chlorella ohadii Photosystem II Reveals Protective Mechanisms against Environmental Stress

“…In the case of the previously described mechanism, when reduced Q B is proposed to leave and be replaced by another oxidized Q B , this step would limit the electron transfer in the PSII part of all the electron-transport chain, and newly arrived electrons will be stuck on the Q A − stage, increasing the probability of forming radicals and damaging PSII subunits. The observation that the plastoquinone pool of Nannochloropsis oceanica was not completely reduced during the bright light pulses [36], as well as in the plants [37], is in line with this study's proposal for the mechanism of photoprotection in C. ohadii.…”

“…trons will be stuck on the QA stage, increasing the probability of forming radicals and damaging PSII subunits. The observation that the plastoquinone pool of Nannochloropsis oceanica was not completely reduced during the bright light pulses [36], as well as in the plants [37], is in line with this study's proposal for the mechanism of photoprotection in C. ohadii.…”

Enhanced Algal Photosynthetic Photon Efficiency by Pulsed Light

“…There is direct experimental evidence, not just correlative evidence, supporting the assumption about how the state of the PQ pool and its saturation affect photosynthetic dynamics (Joliot and Joliot, 1984a, 1984bJoliot, 2003;Rokke et al, 2017;Suslichenko and Tikhonov, 2019). There is comparable additional evidence for the influence of the PQ pool on photosynthetic efficiency from investigations of direct hydrogen production (rather than biomass generation) from algae (Greenbaum, 1979) where the same rate-limiting steps in PS II dominate photosynthetic yield.…”

Plastoquinone In and Beyond Photosynthesis

“…In normal growth conditions, up to 50% of the PQ-9 pool in plant leaves is located in the thylakoid membranes where it participates in electron transport from PSII to the cytochrome b6/f. The number of PQ-9 molecules per PSII has been estimated to be around 10-15 [27,29,30] although some lower values were reported [31]. The total PQ-9 concentration in plants can vary considerably with the environmental conditions, but the amount of photochemically active PQ-9 in the thylakoid membrane seems to be rather constant [27], possibly representing an optimal value for photosynthesis.…”