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q
P
(puddle model parameter)
is the quenching parameter that represents photochemical
quenching. It is a measure of the fraction of still open PSII reaction centers. q
P
is defined as
the coefficients of photochemical fluorescence quenching. The original definition of this term
implied that fluorescence quenching affects primarily the 'variable fluorescence' (Fv) and not
the minimal fluorescence (Fo). In cases where qN is greater than 0.4 this may not be a good
assumption. When qN is above 0.4, Fo’ (or Fod) should replace Fo in qP equations. By using
the Far-Red source for post illumination, the PSII acceptors may be re-oxidized through the
illumination affect on PSI. A new Fod value may be measured and used for corrections to the
quenching coefficients. This assumes the PSI acceptors are properly activated, which may not
be the case in a dark adapted sample. Therefore, the Fod determination should be done after
induction of photosynthesis has been done for several minutes. Numbers range from zero to
one. (Puddle model) (Van Kooten & Snell, 1990)
q
E
(puddle model parameter)
is the quenching parameter that represents the photo-
protective mechanisms in the leaf that allow rapid compensation for changes in light levels
due to cloud cover and increased light intensity. It is directly related to
)
ph of the thylakoid
lumen and the xanthophyll cycle. (Muller P., Xiao-Ping L., Niyogi K. 2001) This process is
completed in two to four minutes after an actinic light is turned on. (Lichtenthaler 1999). It is
delineated as a percent of NPQ by using a quenching relaxation method. Some researchers in
the past have also divided qN into q
E
, q
T
, and q
I
instead of NPQ (Lichtenthaler 1999) The
relaxation characteristics of field plants can vary with changing environmental conditions
(Baker 2008). NPQ is used to determine relaxation coefficients because it has been
resurrected for Klughammer's lake model parameters. Use of q
N
has been discredited in the
lake model.
q
T
(puddle model parameter)
is not true quenching. Instead, the parameter represents state 1
and state 2 transitions. This value is negligible in higher plants at high light levels but may be
substantial at low light levels (Lichtenthaler 1999) (Baker 2008). According to Ruban (2008)
state transitions require between fifteen and twenty minutes to complete. It can be delineated
as a percent of NPQ by using a quenching relaxation method (Muller P., Xiao-Ping L., Niyogi
K. 2001),(Lichtenthaler 1999). For more information on state transitions, and how they affect
fluorescence measurement contact Opti- Sciences for the application note on state transitions.
The relaxation characteristics of field plants can vary with changing environmental conditions
(Baker 2008). NPQ is used to determine relaxation coefficients because it has been
resurrected for Klughammer's lake model parameters. Use of q
N
has been discredited in the
lake model.
q
I
(puddle model parameter)
is the quenching parameter that represents photo-inhibition
and photo-damage. (Puddle model) (Muller P., Xiao-Ping L., Niyogi K. 2001) According to
Lichtenthaler (1999, 2004) chronic photoinhibition starts to relax after forty minutes in the
dark and may take up to sixty hours. It can be delineated from NPQ by using a quenching
relaxation method. The relaxation characteristics of field plants can vary with
