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Hendrickson’s (2004) work offered such a solution with Y(NPQ) measurements that are
consistently and only marginally lower values than Kramer’s work, and Y(NO) measurements
that are consistently and marginally lower except at high light levels and low temperatures
than Kramer’s work. He speculates that the differences in values between Kramer and his
own were possibly due to the difficulties in making Fo’(or Fod) measurements. Furthermore,
Hendrickson does not provide a parameter like qL to estimate the fraction of open PSII
centers.
From Hendrickson’s work, and earlier works by Cailly (1996) and Genty (1989, 1996),
Klughammer and Schreiber derive simplified equations that allow for Hendrickson’s
parameters, and also allow users to reconcile NPQ measurements with the lake model.
The Luke Hendrickson simplified lake model parameter were chosen as the default quenching
protocol for the OS1p.This was done because they are lake model parameters that allow the
resurrection of NPQ from the puddle model by Klughammer, and because relaxation
protocols, available in the puddle model, still work for the Hendrickson lake model. Other
protocols may be selected at the time of purchase, or they may be purchased at a later date.
They include Kramer parameters, puddle model parameters and a quenching relaxation
protocol that works with either the Hendrickson lake model or the puddle model protocols.
The quenching relaxation protocol has been retained because it allows for the separation of
state transition measurements, and photo-inhibition in quenching relaxation protocols. In
standard lake model parameters, they are both part of Y(NO). There is also a significant
volume of work done using the older puddle model parameters that may be valuable for
comparison especially in regard to NPQ.
The loss of light energy from the reaction center as fluorescence comes primarily from the
PSII reaction. When leaves have been dark-adapted, the pools of oxidation-reduction
intermediates in the electron transport pathway return to a oxidized state and quenching
mechanisms relax. At this point a low intensity modulated light turns on and off and the
minimal fluorescence signal, Fo, is measured. The modulate light source is at an intensity too
low to drive photosynthesis but high enough to provide a weak fluorescence signal so it is
ideal for measurement. Upon saturation illumination of a dark-adapted leaf, there is a rapid
rise in fluorescent light emission from PSII as all reaction centers are closed and all the
maximum amount of light is channeled to fluorescence. Multiple turn-overs of the Q
A
molecule occur before maximal fluorescence, Fm, is reached in a healthy leaf. If an Fv/Fm
measurement is being made then this is where the process ends.
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