Non-photochemical quenching

Non-photochemical quenching is the regulated dissipation of excess light energy as heat in photosynthetic organisms, protecting their photosynthetic machinery from photodamage.

Xanthophyll cycle: A cycle of pigment interconversions that helps plants adjust to changing light conditions. Its conversion of violaxanthin to zeaxanthin promotes energy dissipation in many plants.
Photosynthesis: The conversion of light energy into chemical energy by plants, algae, and some bacteria. Quenching is a protective response embedded within the photosynthetic conversion of light.
Chlorophyll fluorescence: Light emitted by excited chlorophyll as it returns to a lower-energy state. Changes in fluorescence provide common measurements of quenching in leaves and algae.
Photochemistry: Light-driven chemical reactions that convert absorbed photon energy into chemical change. Photochemistry stores excitation energy in reaction products; quenching dissipates it as heat.
PsbS: A thylakoid membrane protein that senses lumen acidification and helps initiate energy dissipation in plants. Protonation of PsbS helps trigger rapid quenching in higher plants.
Light-harvesting complex: A pigment–protein assembly that absorbs light and transfers excitation to a photosynthetic reaction center. Quenching competes with this transfer by redirecting excitation into heat.
Pulse-amplitude-modulated fluorometry: A method that uses modulated measuring light and saturating pulses to assess photosynthetic fluorescence. It separates fluorescence signals used to estimate non-photochemical quenching in intact samples.
Fluorescence: Light emission following absorption, as an excited molecule returns to a lower-energy state. Fluorescence releases excitation as photons rather than as heat.
Lumenal acidification: A decrease in pH inside the thylakoid lumen caused by proton accumulation. The proton gradient couples high electron-transport activity to activation of quenching.
Excitation energy: Energy carried by an electronically excited molecule before it is transferred or dissipated. This is the energy that quenching diverts away from photochemistry.

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