Xanthophylls and Excess-Energy Dissipation: A Genetic Dissection in Arabidopsis

Thermal dissipation of excess absorbed light energy is considered to play a key role in regulating light harvesting and electron transport, and to prevent photodamage to the photosynthetic apparatus (1, 2, 3). This harmless dissipation is triggered by an increase in the light-driven ΔpH across the thylakoid membrane and is thought to take place primarily in the light-harvesting complexes associated with PSII. Non-photochemical quenching of chlorophyll fluorescence (NPQ) is widely used as a measure of, and often as a synonym for, this dissipation process. ΔpH-dependent NPQ is usually by far the predominant component of the total NPQ, but other processes such as state changes and photodamage can also cause decreases in PSII fluorescence yield and thus contribute to the measured apparent NPQ. An estimate of their contribution can usually be obtained from the component that fails to relax upon removal of the light-driven proton gradient.