In photosynthetic organisms exposure to high light induces the production of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2), which in part is prevented by non-photochemical quenching (NPQ). As one of the most stable and longest-lived ROS, H2O2 is involved in key signalling pathways in development and stress responses, although in excess it can induce damage. A ubiquitous response to high light is the induction of the xanthophyll cycle, but its role in algae is unclear as it is not always associated with NPQ induction. The aim of this study was to reveal how diurnal changes in the level of H2O2 are regulated in a freshwater algal community.
Using a natural freshwater community of algae comprising Euglena species, benthic Navicula diatoms, Chlamydomonas and Chlorella species, Roach et al. demonstrate diurnal variations in H2O2 levels, with a peak at midday. At this point the algae rapidly scavenge H2O2 rather than excreting it. The algal community therefore responds to and influences the concentrations of environmental H2O2. H2O2 levels are low when the xanthophyll cycle is in operation but no relationships between H2O2 levels and non-photochemical quenching are observed. The antioxidant function of the de-epoxidized forms of the xanthophyll pigments is therefore important in the protection of the thylakoid membranes against oxidative damage.
This article appears in the special issue ROS and NO Reactions in Plants.