High resolution optical spectra in vivo: Photoactive protochlorophyllide in etiolated leaves at 5 K

We describe here high-resolution spectra of etiolated leaves studied by means of selective monochromatic excitation of fluorescence as well as by hole-burning technique at liquid helium temperature. Up to now site selection spectroscopy has not been successfully applied to biologically active chromophores in vivo. Our results demonstrate that even in the presence of specific pigment-protein and pigment-pigment interactions very narrow purely electronic lines can be obtained in the optical spectra of biological systems.