Hi,

 Fv / Fm is a ratio that indicates about the quantum efficiency of photosystem II. PI (performance index) indicates about the efficiency of both photosystems I and II. I see that you are working on drought stress. Here is a paper that may provide additionnal informations for you

https://doi.org/10.1016/j.plaphy.2016.04.046

Thank you @Fatma Bejaoui

Mr Naeem Khan,

Chlorophyll fluorescence and productivity could be measure by estimating the ratio of Fv/ Fm (Quantum Yield) which is variable florescence over maximum florescence of PS II  While Plant vitality could be characterized by performance index (PI). PI reflects the functionality of both photosystems I and II and gives us quantitative information on the current state of plant performance under stress conditions. Detailed information could be found in the following attachments.

Any fluorescence signal emitted from excited chlorophyll of any plant we are measuring, is based on 6 parameters answering the following questions (all starting with a W):

1) Who is fluorescing?.....................describe your plant or your fluorescing sample

2) Where is it fluorescing?...............Indicate the wavelength or filter where you                                                                      measure the fluorescence signal

3) Why is it fluorescing?                   Because the sample is excited: indicate the

                                                         wavelengths of your excitation light (nm or used                                                              filter)                                                                         4) What kind of fluorescence?         direct, prompt or modulated or delayed                                                                            fluorescence kinetics you are measuring (e.g. an                                                            OJIP fluorescence transient: see internet: JIP-                                                                test Strasser) describe the shape of the curve                                                                you see.

5) What amount?                              of fluorescence you see? This is the measured                                                              fluorescence intensity emitted by your sample per                                                          measured sample cross-section.                             6) When?                                          are you measuring the fluorescence intensity (the                                                          time-point of your OJIP-prompt fluorescence trace

                                                     e,g. as Fo to Fm or Fo to F(I) to Fm or Fo to F(J)                                                                    to FI) to Fm or Fo to F(K) to F(J) to F(I) to F(m) 

The JIP-test STRASSER (see internet) will give you some explanations of what these Fluorescence SHAPES may represent on the classical basis which states that: if all RCs are open (open is understood that the reaction center complex has an oxidized Qa and closed is understood that Qa is in the reduced state as Qa-. Therefore the fluorescence transient with high excitation light, of a dark adapted leaf, is going from Fo to Fm passing the intermediate step-phases Fk then Fj then Fi to Fm  (seen as inflection points or often partially as steps (on a log time scale) seen at: labelled K (at 300 us) then labelled J (at 2 to 3 ms) then labelled I at 30 ms ( labelled this way as I for INTERMEDIATE step between Fo and Fm, measured in the past with mechanical shutter instruments, not having safe recordings of faster signals (below 1 ms). Fp as the highest fluorescence intensity measured within the time segment of 1 second emitted by a dark adapted sample of a leaf or algae. With fast shutterless optoelectronics, much faster prompt-fluorescence-kinetics than 1ms for going from darkness to full light intensity reviled intermediate steps in the fast fluorescence kinetics of about the following steps:

from O(? ns) to L(30 us) to K(300 us) to J(3ms) to I(30ms) to H(300ms) (H for Highest or P forPpeak) P(300ms) under saturating light intensity.

Named as kinetic steps or bands in

alphabetical order from longer to shorter time units: O--(N)..(M)--L--K--J--I--H--G--F(t)

Depending on the experimental conditions all these steps can be visualized more or less clearly. A kind of general agreement exists that at time zero of the fluorescence kinetics Fo all reducible RCs are in the oxidized state with Qa and at Fm all reducible RCs are in the reduced state with Qa-.

Below this phenomenologically described fast fluorescence rise-kinetics OKJIP are hidden a succession of redox states of the oxidised RCII.QaQb complex which gets fully reduced as reducedRCII.Qa-Qb= etc.

The Qa to Qa- reduction is therefore called in the literature as PRIMARY PHOTOCHEMISTRY (even so the word "primary" is always questionable.) Nevertheless the reduction of Qa to Qa- is a classical stable reduction. The fluorescence yield of Qa- is higher than the fluorescence yield of the oxidized form Qa. Therefore the phenomenon of variable fluorescence kinetics is a measure of the reduction kinetics of Qa to Qa-.            

Therefore the variable fluorescence kinetics (in vivo or in vitro) is a measure of the reduction within the mixture of  all Qa complexes of different unit types (e.g. small units without Chl b, big units with chl b, non exciton exchanging units (separate pack units) and cooperative units getting reduced to Qa- within a group (grouped pack units). All forms of complexes do exist in green mature samples of leaves and algae. This mixture of heterogeneity of the energy distribution within the photosynthetic apparatus leads morphologically to different types of stroma- and grana-thylakoid formations, leading to different structures and functions of  chloroplasts thylakoids in plants and algae. 

Any questions or comments welcome to:

Reto J. Strasser,  [email protected]

Hofgutweg 51B

CH 3400 BURGDORF

Switzerland 

What is the difference between fv/fm and PI, How they related to chlorophyll fluorescence?

Fatma Bejaoui · 3.38 · Centre de Biotechnologie, Technopole Borj Cédria

Hi,

 Fv / Fm is a ratio that indicates about the quantum efficiency of photosystem II. PI (performance index) indicates about the efficiency of both photosystems I and II. I see that you are working on drought stress. Here is a paper that may provide additionnal informations for you

https://doi.org/10.1016/j.plaphy.2016.04.046

1d ago · Recommended2 Recommendations

Please keep in mind: Quantifying biological functions can be a help, if the assumptions used for the calculations are recognized as well by the biological sample under investigation. Our explanations cannot go further than what the mathematical freedom of the used equation allows. In concrete, for fluorescence signals of plants we define for practical reasons some equations which can accommodate our experimental measurements. At the level of complexity chosen by us, the level of information is restricted. By using fluorescence signals (e.g. for plants chlorophyll fluorescence kinetics), we deal, by a given light intensity and light quality with light absorption phenomena by the sample and light emission phenomena of the excited sample. For the initial and maximal fluorescence intensity ( Fo and Fm of a dark adapted sample) we derive for the AVVERAGE sample the flux ratio of Fo/Fm or (Fm-Fo)/Fm =Fv/Fm =

kP/(kP + kN) (expressed in de-excitation rate constants kP for photochemistry and kN for the sum of all nonphotochemical deexcitation reactions). Or the simplest expression as the ratio (Fv/Fo) = kP/kN

All F-expressions refer to energy fluxes and all kN-expressions refer to de-excitation RATE-CONSTABNTS, therefore to DISTANCES within a structure. No way to get more information. STRUCTURE however refers to the HARDWARE of our sample. Any shape of a functional unit refers to a hardware which we can call and use as "Bioenergetic TAXONOMY". We are measuring FUNCTIONS and we compare with these the STRUCTURES or the TAXA. (e.g. Birds are flying by the use of wings and fishes are swimming etc ). Deriving the performance indices we get a description of our sample in terms of 4 independent probabilities using the Greek symbols: phi, psi, delta and the antenna-size gamma (Antenna Chlorophyll per one Reaction center). According to the Nernst equation each term of the form

log (x/(1-x)) refers to a driving force where x stands for phi, psi, delta and gamma. Therefore Structures and functions become exchangeable or replaceable. Known as Structure-Function relationship. The performance index PI(total) refers to 4 free parameters, distinguishing 4 different de-excitation rate constants and their sum, where one of them is Fv/Fm = kP/(kP+kN) or Fv/Fo = kP/kN

THEREFORE Fv/Fo = kP/kN is a part of the Performance Index among other independent expressions. To go deeper in our understanding we need the fluorescence life-time data, reefering to the sum kP+kN

For more information, concerning your interests and your systems and models, contact me: [email protected]

good luck.

find the attachment