GFPIII operation manual
Opti-Sciences, Inc.
8
Research overview:
Starting with Gitelson (1999): “ The ratio between chlorophyll fluorescence at 735 nm and the
wavelength range 700nm to 710 nm, F735/F700 was found to be linearly proportional to the chlorophyll
content (with determination coefficient, r
2
, more than 0.95) and thus this ratio can be used as a precise
indicator of chlorophyll content in plant leaves.”
Bushmann (2007) comes to the following conclusion regarding red and far red ratio fluorescence: “Thus,
the Chl fluorescence ratio red/far-red represents an ideal tool for detecting differences and changes of Chl
content in plant species and leaf tissues, to monitor changes in Chl content and photosynthetic activity
caused by changing environmental conditions, strain and stress events, and to detect stress tolerance,
mineral deficiency, diseases, and other constraints. It can be applied for non-destructive monitoring of
terrestrial vegetation in basic photosynthesis research as well as in agriculture, horticulture, and forestry.”
The variables:
Fluorescence emission response to chlorophyll content:
As chlorophyll content levels increase, the intensity of the selected far red fluorescence emission at
735 nm increases, and then decline slightly. At the shorter fluorescence emission wavelength, 700 nm, the
value increases and then it declines dramatically.
The Gitelson paper (1999) compares results using various excitation wavelengths and emission
wavelengths. They find good results using various excitation wavelengths and narrower ranges of red
fluorescence emission and far red fluorescence emission. It was found that by moving the red
fluorescence emission wavelength away from the peak near 685nm, to 700nm, fluorescence re-absorption
and re-emission are minimized. Blue excitation tends to penetrate the leaf slightly and so re-absorption of
emitted fluorescent light causing additional fluorescence is less of a problem. These changes allow a large
extension of the linear measuring range of the instrument. According to Bushmann, (2007) with blue
excitation, the fluorescence comes primarily from the mesophyll layer.
