Chlorophyll fluorescence parameters and definitions

Chlorophyll fluorescence parameters and definitions

The chlorophyll fluorescence parameter is a set of variables or constant values ​​used to describe the photosynthesis mechanism and photosynthetic physiological state of plants. It reflects the "inherent" characteristics of plants and is regarded as an intrinsic probe for studying the relationship between plant photosynthesis and environment.

In order to unify the chlorophyll fluorescence parameter names, standard nomenclature was given to most of the above parameters at the International Fluorescence Symposium held in 1990.

The technique commonly used to analyze chlorophyll fluorescence parameters is called chlorophyll fluorescence kinetics , which has a unique role in measuring the absorption, transmission, dissipation, and distribution of light energy by photosynthesis during leaf photosynthesis. Rapid, non-invasive probes for studying plant photosynthetic functions have been gradually applied in the study of effects of environmental stress on plant photosynthesis. Chlorophyll fluorescence techniques are usually available in both modulation and non-modulation. The chlorophyll fluorescence measurement technique is a technique that uses a light source with a certain modulation frequency and intensity to induce a chlorophyll fluorescence emission to be in a certain state by a saturation pulse analysis method to perform corresponding fluorescence detection. That is, the measurement light that excites fluorescence has a certain modulation (on/off) frequency, and the detector only records the fluorescence at the same frequency as the measurement light, so the modulation fluorometer allows measurement of fluorescence under all physiological states; opening a short duration ( Generally, glare of less than 1 s) turns off all electronic gates (photosynthesis is temporarily suppressed), thereby maximizing chlorophyll fluorescence. This technology is convenient for field observations.

Definition of some chlorophyll fluorescence kinetic parameters :

F0: fixed fluorescence, initial fluorescence. Also known as basal fluorescence, 0 horizontal fluorescence, is the fluorescence yield of the photosystem II (PSII) reaction center when it is completely open, which is related to the leaf chlorophyll concentration.

Fm: Maximum fluorescence (maximal fluorescence), which is the fluorescence yield of the PSII reaction center when it is completely shut down. It can reflect the electronic transmission through PSII. Usually the leaves are measured after dark adaptation for 20 min.

F: actual fluorescence intensity at any time.

Fa: fluorescence instable state.

Fm/F0: Reflects the electronic transfer through the PSII.

Fv=Fm-F0: is a variable fluorescence, reflecting the reduction of QA.

Fv/Fm: is the optimal photochemical efficiency of PSIIin the dark or (optimal/maximalquantum yield of PSII), reflecting the intrinsic PSII efficiency or the maximum PSII in the PSII reaction center. The light energy conversion efficiency (optimal/maximal PSII efficiency), measured after the dark adaptation of the leaves for 20 min. Under non-stress conditions, the change of this parameter is extremely small, and is not affected by species and growth conditions. Under the stress condition, the parameter decreases significantly.

Fv'/Fm': PSII photochemical efficiency of PSIIin the light, reflecting the original light energy capture efficiency of the open PSII reaction center, and the leaf is directly measured under light without dark adaptation.

(Fm'-F)/Fm' or ΔF/Fm': PSII actual photochemical efficiency of PSIIin the light (Bilger and Bjrkman, 1990), which reflects the PSII reaction center in the case of partial closure The actual primary light energy capture efficiency, the blade is directly measured under light without dark adaptation.

There are two types of fluorescence quenching: photochemical quenching and non-photochemical quenching. Photochemical quenching: represented by photochemical quenching coefficient: qP=(Fm'-F)/(Fm'-F0'); non-photochemical quenching , there are two representation methods, NPQ=Fm/Fm'-1 or qN= 1-(Fm'-F0') / (Fm - F0) = 1 - Fv' / Fv.

The electron transfer rate of the table sightseeing is expressed as [(Fm'-F)Fm'] × PFD, and can also be written as: △F/Fm'×PFD×0.5×0.84, where the coefficient 0.5 is because one electron transfer needs to absorb 2 quantum And photosynthesis includes two optical systems, a coefficient of 0.84 indicates 84% ​​of the absorbed light quantum, PFD is the photon flux density; and the apparent heat dissipation rate is (1-Fv'/Fm') × PFD Said.

Fmr: the maximum recoverable fluorescence yield, which is obtained after the fluorescence P and M peaks. When the maximum fluorescence yield of the open PSII is stable, after the F0' is turned off by the action light, the flash interval of the saturated light is extended to 180s. / times, the maximum fluorescence yield of a set of increasing (log growth) is obtained, and the maximum fluorescence yield of the set is placed in a semi-logarithmic coordinate system, and the intercept of the straight line on the Y-axis is Fmr. The (Fm-Fmr)/Fmr can reflect the irreversible non-photochemical quenching yield, that is, the possible degree of photoinhibition.