Search

The acclimation of the green algae Chlamydomoas reinhardtii to high light (HL) has been studied predominantly under continuous illumination of the cells. Here, we investigated the impact of fluctuating HL in alternation with either low light (LL) or darkness on photosynthetic performance and on photoprotective responses. Compared to intervening LL phases, dark phases led to (1) more pronounced reduction of the photosystem II quantum efficiency, (2) reduced degradation of the PsbS protein, (3) lower energy dissipation capacity and (4) an increased pool size of the xanthophyll cycle pigments. These characteristics indicate increased photo‐oxidative stress when HL periods are interrupted by dark phases instead of LL phases. This overall trend was similar when comparing long (8 h) and short (30 min) HL phases being interrupted by long (16 h) and short (60 min) phases of dark or low light, respectively. Only the degradation of PsbS was clearly more efficient during long (16 h) LL phases when compared to short (60 min) LL phases. Summary Statement: The performance of the unicellular green alga Chlamydomonas reinhardtii has been studied so far, mostly under continuous illumination conditions. We investigated the impact of fluctuating high light (HL) on the photosynthetic performance and the photoprotective response in C. reinhardtii. Our data indicate that intervening dark phases negatively affect cell growth and lead to a delay of HL acclimation processes, including the activation of energy dissipation. [ABSTRACT FROM AUTHOR]

Summary: Understanding photosynthesis in natural, dynamic light environments requires knowledge of long‐term acclimation, short‐term responses, and their mechanistic interactions. To approach the latter, we systematically determined and characterized light‐environmental effects on thylakoid ion transport‐mediated short‐term responses during light fluctuations.For this, Arabidopsis thaliana wild‐type and mutants of the Cl− channel VCCN1 and the K+ exchange antiporter KEA3 were grown under eight different light environments and characterized for photosynthesis‐associated parameters and factors in steady state and during light fluctuations. For a detailed characterization of selected light conditions, we monitored ion flux dynamics at unprecedented high temporal resolution by a modified spectroscopy approach.Our analyses reveal that daily light intensity sculpts photosynthetic capacity as a main acclimatory driver with positive and negative effects on the function of KEA3 and VCCN1 during high‐light phases, respectively. Fluctuations in light intensity boost the accumulation of the photoprotective pigment zeaxanthin (Zx). We show that KEA3 suppresses Zx accumulation during the day, which together with its direct proton transport activity accelerates photosynthetic transition to lower light intensities.In summary, both light‐environment factors, intensity and variability, modulate the function of thylakoid ion transport in dynamic photosynthesis with distinct effects on lumen pH, Zx accumulation, photoprotection, and photosynthetic efficiency. [ABSTRACT FROM AUTHOR]

Author(s): Vera Bonardi [1, 2, 6]; Paolo Pesaresi [2, 3, 6]; Thomas Becker [1]; Enrico Schleiff [1]; Raik Wagner [4]; Thomas Pfannschmidt [4]; Peter Jahns [5]; Dario Leister (corresponding author) [...]