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Fv/Fm measuring Screen
Fv/Fm Protocol (or Fv/m on the screen) – Background
Dark adapted test - a measurement ratio that represents the maximum potential quantum
efficiency of Photosystem II if all capable reaction centers were open. 0.79 to 0.85 is the
approximate optimal value for most plant species with lowered values indicating plant
stress. (Maxwell K., Johnson G. N. 2000) (Kitajima and Butler, 1975). Fv/Fm has a
photochemical component and a non-photochemical component (Baker 2004). Fv/Fm is a
fast test that usually takes less than two seconds. (see the section on dark adaptation in
chapter 1)
The assumptions are that before the test, PSII is fully oxidized and quenching
mechanisms have relaxed. With the Fv/Fm test, it is important to dark adapt the sample
being tested to get reliable measurements. Fv/Fm dark adaption times can vary due to
light history. Times of twenty minutes to an hour are common. Some scientists only work
with pre-dawn dark-adapted samples. Experiments should be done on plants to be tested
to find the appropriate dark adaption times for best results. Fv/Fm values will be at their
highest amount, and longer dark adaptation times should not increase the value.
A total of 10 dark adaption white clips are provided with the system, to be used for dark
adaption measurement. A clip should be placed on the leaf with the black slider covering
the cylindrical opening. After dark adaption, the end of the fiber optic bundle should be
placed in the cylindrical opening and the dark slide of the clip should be opened allowing
the sample to be exposed to the fiber optic bundle. Dark shrouds can also be used for
dark adaption or lights can be turned off in a windowless environment.
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