Explanation
When the plant is illuminated the fluorescence intensity increases with a time constant in the microsecond or millisecond range. After a few seconds the intensity falls again and finally reaches a steady-state level. The initial rise of the fluorescence intensity (A) is attributed to the progressive saturation of the reaction centers in the photosynthesis. Therefore the quenching of the fluorescence by the photosynthesis decreases with the time of illumination, with a corresponding increase of the fluorescence intensity. The quenching by the photosynthesis pathway is called photochemical quenching. The slow decrease of the fluorescence intensity at later times (B) is termed non-photochemical quenching. Non-photochemical quenching is most likely due to a protection mechanism the plant has to avoid the adverse effect of an excess of light. Several processes cause non-photochemical quenching, e.g. photoinhibition.
Read more about this topic: Kautsky Effect
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