LIGHT‐INDUCED RESPONSES OF OXYGEN PHOTOREDUCTION, REACTIVE OXYGEN SPECIES PRODUCTION AND SCAVENGING IN TWO DIATOM SPECIES¹

Abstract

Diatoms are frequently exposed to high light (HL) levels, which can result in photoinhibition and damage to PSII. Many microalgae can photoreduce oxygen using the Mehler reaction driven by PSI, which could protect PSII. The ability of Nitzschia epithemioides Grunow and Thalassiosira pseudonana Hasle et Heimdal grown at 50 and 300 lmol photons AE m )2 AE s )1 to photoreduce oxygen was examined by mass spectrometric measurements of 18 O 2 . Both species exhibited significant rates of oxygen photoreduction at saturating light levels, with cells grown in HL exhibiting higher rates. HL-grown T. pseudonana had maximum rates of oxygen photoreduction five times greater than N. epithemoides, with 49% of electrons transported through PSII being used to reduce oxygen. Exposure to excess light (1,000 lmol photons AE m )2 AE s )1 ) produced similar decreases in the operating quantum efficiency of PSII (F q ¢ ⁄ F m ¢) of low light (LL)-and HL-grown N. epithemoides, whereas HL-grown T. pseudonana exhibited much smaller decreases in F q ¢ ⁄ F m ¢ than LL-grown cells. HL-grown T. pseudonana and N. epithemioides exhibited greater superoxide and hydrogen peroxide production, higher activities (in T. pseudonana) of superoxide dismutase (SOD) and ascorbate peroxidase (APX), and increased expression of three SOD-and one APX-encoding genes after 60 min of excess light compared to LL-grown cells. These responses provide a mechanism that contributes to the photoprotection of PSII against photodamage.

FLAVODIIRON2 and FLAVODIIRON4 Proteins Mediate an Oxygen-Dependent Alternative Electron Flow in Synechocystis sp. PCC 6803 under CO2-Limited Conditions

“…These conclusions cannot necessarily be extended to cyanobacteria and algae, which seem to have higher Mehler reaction activities than higher plants (Badger et al, 2000). In fact, the diatom Thalassiosira pseudonana showed oxygen photoreduction at a rate of 600 mmol mg 21 Chl h 21 , corresponding to 49% of the electron flux through PSII (Waring et al, 2010). Similarly, the oxygen-dependent electron transport rate contributes 30% of the total electron flux in Symbiodinium sp., a group of symbiotic dinoflagellates of cnidarians, and FLV proteins might be involved (Roberty et al, 2014).…”

Low nutrient availability reduces high‐irradiance‐induced viability loss in oceanic phytoplankton

“…(this study ;Cardol et al 2008). In Thalassiosira pseudonana, alternative electron transport routes do seem to play an important role in addition to NPQ processes in the prevention of photoinhibition (Waring et al 2010). In addition to enhanced photoprotection, T. oceanica reduced light-harvesting capacity during N starvation by a decrease in cellular Chl a concentrations.…”

Oxidative Stress: Antagonistic Signaling for Acclimation or Cell Death?

“…In algae, there is good evidence that the Mehler reaction serves to dissipate significant levels of excess excitation energy (Waring et al, 2010). However, in higher plants, its role as a major sink for the dissipation of excess excitation energy has been questioned (Badger et al, 2000), but this does not exclude that the Mehler reaction activity that is present serves to initiate ROS signaling.…”