Room temperature fluorescence spectra of protochlorophyllide and chlorophyllide forms in etiolated bean leaves

Room-temperature fluorescence emission and excitation spectra of 3-day or 10-day old dark-grown bean (Phaseolus vulgaris L. cv Commodore) leaves were measured. The excitation light was defocused in such way that only a low rate of phototransformation took place and protochlorophyllide (Pchlide) forms could be detected. The spectra were resolved into gaussian components using a new method based on the comparison of the 4th derivative of the experimental spectrum and that of the calculated spectrum, i.e. the sum of the gaussians. In addition to Pchlide emission bands with maxima at 631, 644, 655 and 667 nm which correspond to those described earlier in 77 K spectra, two new and unusally narrow bands were found at 637 and 650 nm. Tn the Chlide region, emission bands were found at 676, 682, 686 and 695 nm. Changes in the relative amplitudes of the Pchlide and Chlide room temperature emission bands as a function of age, of excitation wavelength and in response to a short light flash were studied. A model is given in which dynamic interconversions of the pigment forms are suggested and the presence of the new forms is explained with the differences in the aggregational states of the pigments and with their interaction with NADPH or NADP(+). (C) 1997 Elsevier Science S.A.