HANSATECH FMS1, Manual

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62 FMS 1 - Fluorescence Monitoring System
© 2017 Hansatech Instruments Ltd
3.7.3.2 Light-adapted measurement routines
In the case of light-adapted tissue, a proportion of PSII electron acceptors are reduced, “closing”
some PSII reaction centres. Hence the probability that absorbed energy is used for photochemistry
is not maximal as competing non-photochemical processes are operating ( Section 1 ). The
instrument toolbar allows access to routines which determine the relative extent of each of these
processes. When coupled with measurement of the light-adapted ratio of variable to maximal
fluorescence ratio they permit the estimation of PS II quantum efficiency (PSII) using the model of
Genty et al. 1989.
The phi PSII function
Several measurements of fluorescence yield from the sample in different defined states are
required to estimate
f
PSII. Initially the fluorescence yield of the sample under the ambient light
regime is required (Figure 2-37). Such measurements are often made after a sample has adapted
to a particular light-regime or environment and is operating at steady state. Consequently the
measurement is often referred to as the “steady state” fluorescence yield, Fs (Figure 2-37). A
saturating pulse is then required to “close” all of the PSII reaction centres; the temporary
inhibition of PSII photochemistry ensures that the maximal fluorescence yield is achieved,
Fm’ (Figure 2-37). If a previous dark-adapted measurement of Fv/Fm has been made the extent of
photochemical and non-photochemical quenching processes can be determined from the
equations of Schreiber et al. 1987.
The
f
PSII function automatically executes the protocol shown in boxed area of figure 2-37: