Equations for fluorescence and P700 parameters
Measurements, Protocols & Macros
Kaija Porkka
Nov 2021
Hello, I read the manual and checked some of the references but I still could not understand how some of the parameters measured by MultispeQ (with Photosynthesis RIDES) are calculated. Specifically I was wondering: 1) How is Fm (it should be needed for phiNO and consequently for phiNPQ) determined as there is not (necessarily) any dark acclimation? 2) Does "FvP_over_FmP" equal (Fm’-F0’)/Fm’ ? 3) Would it be possible to get the exact equations for all the P700 parameters (active PSI, open PSI centers, over-reduced PSI and oxidized PSI)? It seems to me that almost all of them require a measurement of (dark acclimated, or non-stressed) Pm? For example, as far as I understand, Kuhlgert et al. 2016 define "active PSI centers" as PM/P0, where PM is P700 signal during a saturating pulse under the studied conditions and P0 P700 signal under similar pulse but under non-stressed conditions. Thank you, Heta
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Nov 2021
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Sebastian
Dec 2021
Hi,
I will try to answer your questions. For some of the calculations, it is best to check the measurement protocols macro, since it is not necessarily all documented in the protocol description.
1) How is Fm (it should be needed for phiNO and consequently for phiNPQ) determined as there is not (necessarily) any dark acclimation?
For the calculation of PhiNO and PhiNPQ you can use the NPQt parameter as it is done in the macro and thus no dark acclimation is needed.
PhiNO = 1/( NPQt + 1 + qL * 4.88 )
PhiNPQ = 1 - Phi2 - PhiNO
This is based on equations 51 and 52 from the publication below:
Kramer, D. M., Johnson, G., Kiirats, O. & Edwards, G. E. New Fluorescence Parameters for the Determination of QA Redox State and Excitation Energy Fluxes. Photosynth Res 79, 209 (2004).
2) Does "FvP_over_FmP" equal (Fm’-F0’)/Fm’ ?
Yes!
3) Would it be possible to get the exact equations for all the P700 parameters (active PSI, open PSI centers, over-reduced PSI and oxidized PSI)?
I think the P700 measurement is based on a publication by Klughammer and Schreiber from looking at the P700 absorbance trace (PSI_data_absorbance).
Klughammer, C. and Schreiber, U. (1994). An improved method, using saturating light pulses, for the determination of photosystem I quantum yield via P700⁺-absorbance changes at 830 nm. Planta 192: 261–268.
In terms of the calculation, this is what I derived from the macro. The measurement is based on the measurement sequence and absorbance values taken at:
- Steady State (actinic light)
- First Saturation Pulse (actinic light)
- Dark Period (far-red light only)
- Second Saturation Pulse (actinic light)
- PS1 Active Centers:
Absorbance 2nd Saturation pulse - PS1 Open Centers: (
Absorbance 1st Saturation pulse-Absorbance Steady State) /Absorbance 2nd Saturation pulse - PS1 Over Reduced Centers: 1 - (
Absorbance 1st Saturation pulse/Absorbance 2nd Saturation pulse) - PS1 Oxidized Centers:
Absorbance Steady State/Absorbance 2nd Saturation pulse)
I hope this helps
~ Sebastian