PP Systems CIRAS-2, Руководство оператора

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Brief Introduction to Chlorophyll Fluorescence
CIRAS-2 Operator's Manual Version 2.04
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groups have become known as photosystem I and photosystem II. In practice, differences in the
functionality of photosystem I and II mean that at least 95% of the chlorophyll fluorescence signal
observed under physiological temperatures is derived from chlorophyll molecules associated with
photosystem II (PSII). Hence the fluorescence signal detected by CFM-1 reflects changes in the efficiency
with which absorbed light is used for PSII photochemistry.
Techniques for Measuring Chlorophyll Fluorescence.
Photosynthesising organisms only fluoresce when illuminated with visible light. Within the normal
physiological temperature range, peak fluorescence occurs in the red region of the spectrum ( 685 nm)
and extends into the infra-red region to around 800 nm (Krause and Weiss 1984) (Figure 1-1).
Figure 1-1. Room temperature chlorophyll fluorescence emission spectra. (Adapted from
Krause and Weiss 1984)
Therefore, accurate determination of fluorescence requires a detection system that is sensitive to the
fluorescence wavelengths yet blind to the actinic (or excitation) light, which drives photochemistry.
There are 2 methods commonly used by commercial instruments.
1. Continuous Excitation Systems
In continuous excitation instruments such as the HANSATECH PEA (
Plant Efficiency Analyser) signal
discrimination is achieved using a custom designed 650 nm actinic light source to drive photochemistry;
optical filtering of the detector then prevents detection of non-fluorescence wavelengths of light.
Unfortunately, such systems must be shielded from ambient light during use. Otherwise, the red / far-red
component of daylight will be super-imposed on the fluorescence signal.
2. Modulated Systems
This problem is avoided in instruments such as the HANSATECH FMS2 and in the CFM by using an
electronic method, commonly referred to as modulated fluorometry, to separate actinic light from the
fluorescence signal (Ögren and Baker 1985). During measurement the tissue sample is exposed to a
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