biophysics Biophysics is an interdisciplinary science that applies approaches and methods traditionally used in physics to study biological phenomena. Biophysics covers all scales of biological organization, from molecular to organismic and populations ...

, the Kautsky effect (also fluorescence transient, fluorescence induction or fluorescence decay) is a phenomenon consisting of a typical variation in the behavior of a plant fluorescence when exposed to light. It was discovered in 1931 by H. Kautsky and A. Hirsch. When dark-adapted photosynthesising cells are illuminated with continuous light,

chlorophyll fluorescence Chlorophyll fluorescence is light re-emitted by chlorophyll molecules during return from Excited state, excited to non-excited states. It is used as an indicator of photosynthetic energy conversion in plants, algae and bacteria. Excited chlorop ...

displays characteristic changes in intensity accompanying the induction of photosynthetic activity.

Application of Kautsky effect

The quantum yield of photosynthesis, which is also the photochemical quenching of fluorescence, is calculated through the following equation: Φ_p = (F_m-F₀)/F_m = F_v/F_m F₀ is the low fluorescence intensity, which is measured by a short light flash that is not strong enough to cause

photochemistry Photochemistry is the branch of chemistry concerned with the chemical effects of light. Generally, this term is used to describe a chemical reaction caused by absorption of ultraviolet (wavelength from 100 to 400 Nanometre, nm), visible ligh ...

, and thus induces fluorescence. F_m is the maximum fluorescence that can be obtained from a sample by measuring the highest intensity of fluorescence after a saturating flash. The difference between the measured values is the variable fluorescence F_v.

Explanation

The Kautsky effect When a sample (leaf or algal suspension) is illuminated, the fluorescence intensity increases with a time constant in the microsecond or millisecond range. After a few seconds the intensity decreases and reaches a steady-state level. The initial rise of the fluorescence intensity is attributed to the progressive saturation of the reaction centers of photosystem 2 (PSII). Therefore, photochemical quenching increases with the time of illumination, with a corresponding increase of the fluorescence intensity. The slow decrease of the fluorescence intensity at later times is caused, in addition to other processes, by

non-photochemical quenching Non-photochemical quenching (NPQ) is a mechanism employed by plants and algae to protect themselves from the adverse effects of high light intensity. It involves the quenching of singlet excited state chlorophylls (Chl) via enhanced internal conv ...

. Non-photochemical quenching is a protection mechanism in photosynthetic organisms as they have to avoid the adverse effect of excess light. Which components contribute and in which quantities remains an active but controversial area of research. It is known that

carotenoids Carotenoids () are yellow, orange, and red organic compound, organic pigments that are produced by plants and algae, as well as several bacteria, archaea, and Fungus, fungi. Carotenoids give the characteristic color to pumpkins, carrots, parsnips ...

and the special pigment pairs (e.g.

P700 P700, or photosystem I primary donor, is a molecular dimer of chlorophyll ''a'' associated with the reaction-center of photosystem I in plants, algae, and cyanobacteria. Etymology Its name is derived from the word “pigment” (P) and the ...

) have functions in

photoprotection Photoprotection is the biochemical process that helps organisms cope with molecular damage caused by sunlight. Plants and other oxygenic phototrophs have developed a suite of photoprotective mechanisms to prevent photoinhibition and oxidative str ...

References

* * * * * Fluorescence Biophysics Optical phenomena Fluorescence techniques Energy transfer Photosynthesis {{spectroscopy-stub