Changes of Chlorophyll Fluorescence Signatures during Greening of Etiolated Barley Seedlings as Measured with the CCD-OMA Fluorometer

Abstract

In greening barley seedlings the chlorophyll fluorescence emmission spectra were recorded by the Karlsruhe CCD-OMA spectrofluorometer during the fast rise (fast component of Kautsky effect) and the slow decline (slow component of Kautsky effect) of the chlorophyll fluorescence kinetics. The relationships between fluorescence signatures and photosynthetic pigments were used to characterize the development of photosynthetic activity in 7d old etiolated barley seedlings during illumination with continuous white light, The shape of the chlorophyll fluorescence spectra exhibited characteristic changes during the greening of etiolated barley seedlings. At the onset of greening and a very low chlorophyll content only one fluorescence peak near 690 nm was detectable, whereas the second fluorescence peak near 735 nm, initially expressed only as a shoulder, was developed during the chlorophyll accumulation to a separate fluorescence maximum. The time course of the fluorescence intensity near 690 nm and 735 nm at maximum (fm) and steady-state of the chlorophyll fluorescence (fs) can be explained on the basis of a partial reabsorption of the emitted red chlorophyll fluorescence band F690 by the leaf chlorophyll. The chlorophyll fluorescence ratios F690/F735 at fm and fs were determined from the CCD-OMA spectra. The decreasing of the chlorophyll fluorescence ratio F690/F735 with increasing chlorophyll content during greening of the etiolated barley leaves can be expressed by a power function (curvilinear relationship): y=ax-b. The variable chlorophyll fluorescence decrease ratios (Rfd-values) as vitality index were calculated from the fluorescence intensities measured at 690 nm and 735 nm of the CCD fluorescence spectra. The Rdf690 and Rfd735 values increased during greening and exhibited the characteristics of a saturation curve. The latter was reached for Rfd690 after 24 h of illumination (chlorophyll content 14 μm-2) and for Rfd735 already after 6h of illumination (chlorophyll content 8 μ cm-2). The Karlsruhe CCD-OMA spectrofluorometer is excellently suited for photosynthetic studies as well as stress detection in plants.