FLUORESCENCE OF PHYTOCHROME IN THE CELLS OF DARK‐GROWN PLANTS AND ITS CONNECTION WITH THE PHOTOTRANSFORMATIONS OF THE PIGMENT

Abstract Fluorescence of phytochrome is found in the cells of etiolated monocotyledonous and dicotyledonous plants. The red light‐absorbing form of phytochrome (Pr) fluoresces at 77 K with a yield 0.3±0.1 and maxima at 672–673 nm and 684–686 nm in the excitation and emission spectra, respectively. The emission is characterized by the sharp temperature dependence of its intensity, its high (∼ 40%) polarization, and the violation of the mirror symmetry rule. Connection of the fluorescence with Pr photoreactions is followed in the interval 77–293 K. A P, photoproduct, lumi‐R, is fluorescent with maxima at 696 nm and 705 nm in the excitation and emission spectra; the far‐red light absorbing form of phytochrome (Pfr) is practically nonfluorescent. Three isochromic emitting Pr species are present differing in their photochemical properties: Pr1 and Pr2 which phototransform irreversibly and reversibly at T 170 K into lumi‐R, and lumi‐R2, respectively, and Pr3 which undergoes photoconversion only at T > 240 K. The activation energies of Pr2 and Pr3 photoreactions are evaluated to be 2.9–3.3 kJ/mol and 26 kJ/mol. Complex dynamics of changes of Pr fluorescence and of the extent of its decrease in the photoconversion Pr? Pfr in germinating pea and bean seeds suggests the existence of two Pr pools one of which is incapable of Pr? Pfr phototransformation. Thus, the developed fluorescent method of phytochrome assay and investigation in the cell revealing multiplicity of phytochrome states in vivo proves to be very sensitive (about 1 ng) and informative.