HANSATECH FMS1, Manual

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60 FMS 1 - Fluorescence Monitoring System
© 2017 Hansatech Instruments Ltd
Fo (fluorescence origin)
The fluorescence origin (Fo) is defined as the fluorescence yield following dark adaptation when
all of the PSII reaction centres and electron acceptor molecules are fully oxidised and hence
“open” for photochemistry. As a result Fo is often measured at the beginning of an experiment
when only the modulating beam is illuminated.
The “Fo” button triggers data averaging over a 1.6 sec period with the result stored as Fo in the
“Parameter Window”. It is important to note that this function cannot determine whether the
sample is correctly dark adapted. Hence if it is used in the presence of ambient light or if the
output from the modulating beam is bright enough to drive significant photochemistry ( Testing the
FMS ), the Fo value stored will not relate to the common definition of Fo.
Fm (fluorescence maximum)
The maximum fluorescence yield (Fm) is attained when the dark-adapted sample is exposed to an
intense saturating pulse of light. This temporarily reduces all PSII electron acceptors preventing
PSII photochemistry. The temporary absence of competition from photochemistry for absorbed
energy ensures maximum fluorescence emission from the sample. The “Fm” button initiates a
saturating pulse
of light using the intensity and duration settings specified in the respective “Pulse” edit boxes
( The Saturating Light Source ). During the pulse the fluorescence rise is monitored with the highest
average of two consecutive points stored as the Fm value in the “Parameter Window”. As a result
the Fm value that is presented will be slightly different to the maximum fluorescence value
observed in a tabulated output of the full data set. This procedure is used to minimise the effects
of random noise on the accuracy of the measurement.
Fv/Fm (Maximum quantum efficiency of PSII photochemistry)
The difference between the Fo and Fm fluorescence yield relates the maximum capacity for
photochemical energy quenching by the sample (Figure 2-35) and is defined as variable
fluorescence (Fv).