High light acclimation in green microalgae in Non-Photochemical Quenching and Thermal Energy Dissipation In Plants, Algae and Cyanobacteria
Résumé
Absorption of light in excess of the capacity for photosynthetic electron transport can be detrimental for photosynthetic organisms. Mechanisms exist to protect chloroplasts from damage, which are in general associated with photosystem II and collectively assessed via non-photochemical quenching (NPQ) of chlorophyll fluorescence. Non-photochemical quenching comprises several components, including (1) qE (high-energy state quenching, as the rapid component of NPQ) as a measure of thermal dissipation linked to the development of a low pH in the thylakoid lumen and possibly (2) qT (state transition-dependent quenching, as the slower component of NPQ) as a measure of antenna size reduction involving phosphorylation and migration of antenna proteins from PS II to PS I. The relative amplitude and efficiency of these processes is extremely variable in different photosynthetic organisms (the relative amplitude of the latter is especially more prominent in microalgae than vascular plants), likely reflecting the different molecular machineries and/or regulation of the effectors for the processes underlying qE and state transitions in these organisms. The present review focuses on NPQ in green microalgae and summarizes changes in the latter two NPQ components in photosynthetic microalgae (in particular green algae including Ostreococcus, Chlamydomonas, Dunaliella, and Chlorella). We also relate these changes to possible differences between their molecular machineries, which reflect specific responses of each organism to the constraints existing in its environmental niche. Moreover, alternative photoprotective responses based on changes in the electron flow modes/efficiencies are also presented along with an interpretation as to how these mechanisms can provide a benefit for specific photosynthetic organisms.