CHAPTER 3 PAM FLUOROMETRY & SAT PULSE ANALYSIS
During actinic illumination, a proton gradient across the photosynthetic
membranes (
Δ
pH) is formed and the xanthophyll, zeaxanthin, is synthe-
sized. The
Δ
pH and the concentration of zeaxanthin represent significant
factors for stimulating non-photochemical quenching. Subsequent to il-
lumination, the pH gradient collapses and the zeaxanthin is retrans-
formed into violaxanthin (sketched in Fig. 3.2).
Importantly, the far red-stimulated opening of PS II reaction centers oc-
curs faster than the
Δ
pH collapse and zeaxanthin retransformation. Con-
sequently, in the presence of far red illumination, the minimum fluores-
cence level right after actinic light exposure represents the fluorescence
yield of open PS
II reaction centers with the previous non-
photochemical quenching still present. Without far red illumination, the
velocities of reaction center opening and
Δ
pH breakdown would be
comparable so that PS II reaction centers become fully open only after a
considerable part of non-photochemical quenching has decayed.
In conclusion, the primary information of saturating pulse analysis is:
(1) the fluorescence increase caused by the decrease from maximum to
minimum photochemical quenching in the dark-acclimated and light-
exposed leaf (F
M
minus F
0
and F
M
’ minus F
0
’, respectively). (2) the fluo-
rescence decrease caused by actinic light-activated non-photochemical
quenching in the absence and at maximum photochemical quenching
(F
M
minus F
M
’ and F
0
minus F
0
’, respectively), and (3), derived from the
position of the induction curve just before the saturating pulse (the F´
level) relative to the interval delimited by F
M
’ and F
0
’, the degree of
PS II reaction center closure.
Usually, not absolute fluorescence values or fluorescence differences are
used to measure the PS II state but fluorescence quotients. The fluores-
cence quotients calculated by the WinControl-3 program are summa-
rized in Table 6.1 (Chapter 6). Some publications providing background
information to the various evaluation methods used in saturating pulse
analyses are compiled in sections 6.5 and 7.
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