Time Marks Parameters

The PEA Plus and M-PEA Plus software packages extract chlorophyll fluorescence values from the recorded data from Handy PEA+, Pocket PEA and M-PEA chlorophyll fluorimeters at 5 pre-defined Time Marks. The times are:

  • T1 = 50 microseconds
  • T2 = 100 microseconds
  • T3 = (K step) 300 microseconds
  • T4 = (J step) 2 milliseconds
  • T5 = (I step) 30 milliseconds

Chlorophyll fluorescence values at these Time Marks are used to derive a series of further biophysical parameters, all referring to time base 0 (onset of fluorescence induction), that quantify the photosystem II behaviour for (A) The specific energy fluxes (per reaction center) for:

  • Absorption (Abs/RC)
  • Trapping (TRo/RC)
  • Dissipation (DIo/CS)
  • Electron transport (ETo/RC)

and (B) the flux ratios or yields:

  • Maximum yield of primary photochemistry (\Phi Eo = TRo/ABS)
  • Efficiency (\Psi o=Eto/Tro) with which a trapped exciton can move an electron into the electron transport chain further than Q_{A-}
  • Quantum yield of electron transport (Eto/CS)

The concentration of active PSII reaction centers per excited cross section (RC/CS) is also calculated.

Performance Index Parameters (OJIP Analysis)

The Performance Index (PI) is essentially an indicator of sample vitality. It is an overall expression indicating a kind of internal force of the sample to resist constraints from outside. It is a Force in the same way that redox potential in a mixture of redox couples is a force. Exactly the PI is a force if used on a log scale. Therefore we say:

log PI = Driving~Force~DF

PI is derived according to the Nernst equation. It is the equation which describes the forces of redox reactions and general movements of Gibbs free Energy in biochemical systems. Such a force (or potential = force) is defined as:-

Potential = log x/(1-x)

where x is the fraction of a partner in the reaction A to B. Therefore:

X = A /(A + B)

and if you now convert to:

X/(1-X) = A / B

or for redox reactions

log (red)/(ox)

Now the total potential in a mixture is the sum of the individual potentials or:

Potential~total = log X1/(1-X1) + log X2/(1-X2) ….etc

In our case PI (on an absorption basis or on a chlorophyll basis) has three components:

The first component shows the force due to the concentration of active reaction centers

X1 = RC~Chlorophyll~per~total~chlorophyll = CHL(RC)/CHL(total)


X1/(1-X1) = CHL(RC) / ( CHL(tot) - CHL(RC)) = CHL(RC) / CHL(antenna) = RC/ABS

RC/ABS is a parameter of the JIP test and it is related to the force generated by the RC concentration per antenna chlorophyll.

The second component is the force of the light reactions, which is related to the quantum yield of primary photochemistry:

\Phi(Po) = maxTrapping / Absorption = TRo/ABS = Fv/Fm

The driving force of the light reactions is therefore:

DF(\Phi(Po)) = log PHI/(1 - \Phi) = log (Fv/Fm) / ( 1 - Fv/Fm) = log Fv/Fo = log kP/kN

The third component is the force related to the dark reactions (after Q_{A-}). These are normal redox reactions in the dark.Expressed by the JIP test as:

\Psi(o) = ETo/TRo = (1 - Vj)

Where Vj = relative variable fluorescence at 2 ms or at the step J therefore:

Vj = (Fj - Fo)/(Fm - Fo)~and~\Psi(o) = 1 - Vj = (Fm - Fj) / (Fm - Fo)

Therefore the force of the dark reactions is:

DF(\Psi) = log \Psi/(1-\Psi) = log (1-Vj)/Vj

Now all three components together make:

DF (total~on~a~chl~basis) = DF(RC) + DF(\Phi) + DF(\Psi)

or without log

PI(abs) = RC/ABS \times \Phi/(1-\Phi) \times \Psi/(1-\Psi)

or in fluorescence terms:

PI(abs) = ((dV/dto)/Vj) \times Fm/Fv \times (Fv/Fo) \times (Fm-Fj)/(Fj-Fo)

A more detailed derivation and explanation is beyond the scope and intention of this web page. Further detailed information may be obtained from the following publications which may be downloaded as PDF documents from the following links.

R.J. Strasser, A. Srivastava and M. Tsimilli-Michael
The fluorescence transient as a tool to characterize and screen photosynthetic samples.

Strasser, R.J., M. Tsimilli-Michael and Srivastava, A.
Analysis of the Fluorescence Transient.