REGULATION OF LIGHT HARVESTING IN GREEN PLANTS

TLDR

Plants exposed to excess light trigger nonphotochemical dissipation of excitation energy as a photoprotective mechanism of photosystem II, mediated by dynamic properties of chlorophyll a/b light‑harvesting complexes that sense energy levels via the thylakoid proton gradient and dissipate excess as heat, with the quencher’s nature and dissipation capacity varying with light‑harvesting composition. The paper reviews the molecular mechanisms underlying nonphotochemical energy dissipation and assesses prospects for future progress in understanding light‑harvesting regulation. The review focuses on the molecular mechanisms of nonphotochemical quenching, including the role of chlorophyll a/b light‑harvesting complexes and thylakoid proton gradients. The review assesses that future progress in understanding light‑harvesting regulation is promising.

Abstract

When plants are exposed to light intensities in excess of those that can be utilized in photosynthetic electron transport, nonphotochemical dissipation of excitation energy is induced as a mechanism for photoprotection of photosystem II. The features of this process are reviewed, particularly with respect to the molecular mechanisms involved. It is shown how the dynamic properties of the proteins and pigments of the chlorophyll a/b light-harvesting complexes of photosystem II first enable the level of excitation energy to be sensed via the thylakoid proton gradient and subsequently allow excess energy to be dissipated as heat by formation of a nonphotochemical quencher. The nature of this quencher is discussed, together with a consideration of how the variation in capacity for energy dissipation depends on specific features of the composition of the light-harvesting system. Finally, the prospects for future progress in understanding the regulation of light harvesting are assessed.