Fluorescence lifetimes of protochlorophyllide in plants with different proportions of short-wavelength and long-wavelength protochlorophyllide spectral forms[para]

Photochemistry and Photobiology, Aug 2003 by Mysliwa-Kurdziel, Beata, Amirjani, Mohammad R, Strzalka, Kazimierz, Sundqvist, Christer

Phase and modulation data were analyzed using a multiexponential model of fluorescence decay. In most cases, two (or one) components of fluorescence decay were found. For some results, however, an additional component had to be applied to minimize the [chi]^sup 2^ level and to obtain values of the lifetimes and fractional intensities consistent with those from other repetitions. This additional component always had a very long and unstable lifetime value, and it is not discussed in this study.

Results obtained for different leaves of the same plant species show a high variability of both fluorescence lifetime values and fractional intensities. Thus, at least three series of experiments consisting of 3-10 repetitions for each excitation-emission wavelength were analyzed. Finally, the average fluorescence lifetime was calculated for each of the excitation-emission wavelengths. To preserve information about variability among different leaves, the corresponding fractional intensities were not averaged; instead, the range of fractions found for all repetitions is discussed.

Results of fluorescence lifetime analysis for wild-type pea and the lip1 mutant are summarized in Table 1. For the lip1 mutant excited at 440 nm, one fluorescence lifetime was found for emissions between 633 and 642 nm as well as for 670 nm. Two components of the fluorescence lifetime were observed for 656 nm emission and also for the excitation at 460 nm and emissions at 642 and 656 nm. In the last case, the fast component had a lifetime value about two times longer for the emission at 642 nm than at 656 nm. On the contrary, its fractional intensity was lower. The decrease of the fast component concomitant with the increase of the fractional intensity was observed also when comparing the results obtained for emission at 656 nm and the two excitations 440 and 460 nm.

For wild-type pea leaves excited at 440 nm, two fluorescence lifetime components were found for all the investigated emission wavelengths. The fast component varied between 0.26 and 0.56 ns, and its fraction ranged from 0.12 to 0.34. The slow component had a lifetime between 5.7 and 7.0 ns. For the emission wavelength of 642 nm the slow component found for wild-type pea had a slightly lower value than the slow component found for lip1. For the excitation at 460 nm, two lifetime components were found for the emission at 656 nm, whereas only one component was determined for emissions at 642 and 670 nm.

On the basis of the lifetime results, DAS were calculated for fluorescence lifetime components for both wild-type pea and the lip1 mutant (Fig. 8). DAS is the fluorescence spectrum corresponding to an individual fluorescence lifetime component. In wild-type pea leaves there was a strong resemblance between the steady-state fluorescence emission spectrum (Fig. 3) and the DAS obtained for both the slow- and the fast-lifetime components (Fig. 8). For the lip1 mutant, only the DAS obtained for the slow-fluorescence lifetime component had similarity to the fluorescence steady-state spectrum (Fig. 4).