CHAPTER 5 IMPORTANT POINTS
5 Important Points for Correct YIELD-
Measurements
The main purpose of the MINI-PAM is the reliable determination
of the YIELD-parameter ∆F/Fm (Genty-parameter). This task is
carried out by the MINI-PAM with exceptional sensitivity and
reproducibility. Because of the central importance of this particular
type of measurement, a special section is devoted to it in this
handbook (see section 12.3). Here just the most important practical
aspects are outlined which are essential for correct YIELD-
measurements:
1) The distance between sample and fiberoptics should be approx.
10-15 mm, such that a normal leaf at standard settings gives a
signal of 200-500 units.
2) The AUTO-ZERO function (MODE-menu point 2) should be
applied (while sample is removed), in order to suppress any
unavoidable background signal which otherwise would cause
some lowering of the YIELD-reading (see 12.3.3).
3) In practice, YIELD-measurements make sense only, if the light
conditions of the sample are well controlled. For example, a leaf
may be severely damaged in Calvin cycle activity and still show a
high YIELD-value when dark-adapted or in weak light. The
overall
photosynthetic performance should be assessed during
steady state illumination at a photon flux density which is
somewhat below saturation in a control sample. For highest
accurracy it is essential that the PAR is measured close to the spot
of the sample where also fluorescence is detected. For this
purpose the optional Leaf-Clip Holder 2030-B is available (see
8.3). On the basis of the measured YIELD- and PAR-data an
apparent electron transport rate (ETR) is calculated and displayed
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