Walz MINI-PAM-II, Manual, Page: 38 / 130

Chapter 5 Saturation Pulse Analysis
32
in both the dark-acclimated and light-exposed state (Table 3,
page 34).
Because PAM fluorescence is excited by µs pulses of constant
amplitude, variations between fluorescence levels are usually in-
terpreted as variation in chlorophyll fluorescence yield. This ap-
plies for variations between different types of fluorescence levels
(e.g. between F
0
and F
M
) and for variations of the same type of
fluorescence level (e.g. the change of F
M
’ during a fluorescence
induction curve).
5.1.1 Measurements with Dark-Acclimated Samples
F
0
Minimum fluorescence level excited by very low intensi-
ty of measuring light to keep PS II reaction centers
open.
F
M
Maximum fluorescence level elicited by a pulse of satu-
rating light (Saturation Pulse) which closes all PS II re-
action centers.
5.1.2 Measurements with Illuminated Samples
F
0
’ Minimum fluorescence level of illuminated sample. The
F
0
’ is lowered relative to F
0
by non-photochemical
quenching. The measuring routine for F
0
’ (F
0
’ Mode,
Fig. 39, page 72) determines the F
0
’ level during a dark
interval following a Saturation Pulse. In this dark inter-
val, far red light is applied which selectively drives PS I.
As a consequence, electrons are removed from the in-
tersystem electron transport chain and opening of PS II
reaction centers is efficiently accelerated (see Fig. 22,