Photosystem II cycle activity and alternative electron transport in the diatom Phaeodactylum tricornutum under dynamic light conditions and nitrogen limitation

Abstract

Alternative electron sinks are an important regulatory mechanism to dissipate excessively absorbed light energy particularly under fast changing dynamic light conditions. In diatoms, the cyclic electron transport (CET) around Photosystem II (PS II) is an alternative electron transport pathway (AET) that contributes to avoidance of overexcitation under high light illumination. The combination of nitrogen limitation and high-intensity irradiance regularly occurs under natural conditions and is expected to force the imbalance between light absorption and the metabolic use of light energy. The present study demonstrates that under N limitation, the amount of AET and the activity of CETPSII in the diatom Phaeodactylum tricornutum were increased. Thereby, the activity of CETPSII was linearly correlated with the amount of AET rates. It is concluded that CETPSII significantly contributes to AET in P. tricornutum. Surprisingly, CETPSII was found to be activated already at the end of the dark period under N-limited conditions. This coincided with a significantly increased degree of reduction of the plastoquinone (PQ) pool. The analysis of the macromolecular composition of cells of P. tricornutum under N-limited conditions revealed a carbon allocation in favor of carbohydrates during the light period and their degradation during the dark phase. A possible linkage between the activity of CETPSII and degree of reduction of the PQ pool on the one side and the macromolecular changes on the other is discussed.

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

“…Past bench-top studies employed 3 cm-deep rectangular photobioreactors for culture maintenance, to reduce selfshading effects. These studies observed higher levels of NPQ capability and modeling of photophysiology suggested a high degree of AET in excess light [26,63]. This scenario represents what could occur in shallow, non-turbid natural waters.…”

“…AET rates were not quantified here. However, modeling of Phaeodactylum photophysiology under a sinusoidal light regime predicted that AET could represent an important proportion of the total electron transport in thylakoids [26,63]. The proportion of electrons consumed by AET, measured as light dependent oxygen consumption, increased with increasing growth irradiance in the centric diatom Thalassiosira pseudonana, suggesting AET can be an important component for maintaining redox balance in excess light [21].…”

“…The proportion of electrons consumed by AET, measured as light dependent oxygen consumption, increased with increasing growth irradiance in the centric diatom Thalassiosira pseudonana, suggesting AET can be an important component for maintaining redox balance in excess light [21]. PSII cyclic electron flow [63], a plastid terminal oxidase, the transfer of reduced carbon compounds to the mitochondria for oxidation [64], or the Mehler reaction could be the mechanism of AET in diatoms. It appears likely that AET significantly contributed to photoprotection in our experiments given the low NPQ values in situ.…”

Night Light-Adaptation Strategies for Photosynthetic Apparatus in Yellow-Poplar (Liriodendron tulipifera L.) Exposed to Artificial Night Lighting

“…The PSII as the heart of the photosynthetic process is highly sensitive to the environmental stresses. Its activity could be determined with one non-invasive time-resolved fluorescence measurement, which could measure the polyphasic rise with the basic steps of OJIP [43,[48][49][50][51][52][53][54]. Several studies have shown that the chlorophyll a transient has become one of the most popular tools to estimate stress-induced changes in photosynthetic performance.…”

Contrasting NPQ dynamics and xanthophyll cycling in a motile and a non‐motile intertidal benthic diatom

“…Rapid changes in light climate in well mixed waters or on intertidal flats challenge planktonic and benthic diatoms, respectively, to adjust light harvesting to what can be safely used for photosynthesis. As periods of high light conditions can result in oxidative damage to, in particular, the photosystem II (PSII) core, diatoms possess various mechanisms to deal with high light stress: (1) avoid excess light energy absorption by decreasing cell pigment content (MacIntyre et al ), (2) dissipate excess excitation energy as heat in a process called Non‐Photochemical Quenching of chlorophyll a (Chl a ) fluorescence (NPQ) (Lavaud and Goss ; Goss and Lepetit ), and/or by engaging alternative electron cycling pathways (Wagner et al ), (3) scavenge reactive oxygen species (ROS) (Janknegt et al , 2009 a , b ; Waring et al ), (4) repair damaged PSII cores, mainly by replacing the D1 protein of the PSII reaction center (Wu et al ; Lavaud et al ), (5) behavioral down regulation through vertical cell movement (microcycling and bulk migration) (Kromkamp et al ; Serôdio ). Of the above mechanisms, especially NPQ is able to track fast light fluctuations experienced in the natural habitat (Brunet and Lavaud ; Lavaud and Goss ).…”