Time-resolved spectral studies of blue-green fluorescence of leaves, mesophyll and chloroplasts of sugar beet (Beta vulgaris L.)

Synchrotron radiation and the time-correlated single-photon-counting technique were used to investigate the spectral and time-resolved characteristics of blue-green fluorescence of leaves, mesophyll and chloroplasts. Four kinetic components were resolved. Decay-associated spectra and comparative analysis showed that the fluorescence of leaves, on both sides, was dominated by the fast (0.3 ns) and the medium (1 ns) kinetic components, comprising fluorophores emitting principally in the blue and present in the epidermal layer. In the mesophyll, these two faster components have two maxima, in the blue and in the green part of the spectrum, with a shift of the blue maxima to longer wavelengths when compared to leaves. The slow component (3.5 ns) was green-related with a strong indication for the presence of flavins. The very slow component (9 ns) had a maximal fractional intensity in mesophyll and was blue-related. The excitation and emission characteristics and the effect of anaerobic atmosphere on the fractional intensities of the slow and very slow component showed that they contain fluorescence of flavin nucleotides and nicotinamide nucleotides, respectively. Time-resolved measurements could be a means to extract the information on nucleotide fluorescence from the overall leaf fluorescence, and therefore to evaluate changes in mesophyll redox sate.