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ACTION SPECTRA OF PHYTOCHROME IN VIVO *
Author(s) -
Seyfried Max,
Schäfer Eberhard
Publication year - 1985
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1985.tb08947.x
Subject(s) - phytochrome , mole fraction , cucurbita pepo , in vivo , absorption (acoustics) , action spectrum , mole , spectral line , analytical chemistry (journal) , attenuation coefficient , fluence , in situ , absorption spectroscopy , chemistry , materials science , biophysics , botany , optics , biology , physics , biochemistry , chromatography , red light , laser , microbiology and biotechnology , organic chemistry , astronomy
— A method is described to determine spectral properties of phytochrome in vivo. For photochrome in 7‐day‐old dark‐grown Cucurbita pepo L. seedlings the mole fraction of the far‐red‐absorbing form (P fr ) present at photoequilibrium at 664 nm was found to be 0.76 ± 0.02 in vivo . Based on reflectance measurements, the photon fluence rate just below the surface of the cotyledons was calculated. Local rates of photoconversion for known local fluence rates were measured across cotyledons after non‐saturating irradiations with wavelengths between 544 and 781 nm and in situ molar photoconversion coefficients were obtained. In contrast to purified oat phytochrome, the in situ molar photoconversion coefficients for P fr show a strong shoulder between 660 and 700 nm. The maximum of P fr absorption is at 726 nm. An isosbestic point of phytochrome is found at 686 nm. The mole fraction of P fr present at photoequilibrium with 686 nm light is 0.58. The ratio of photoconversion quantum yields (that for P r → P fr divided by that for P fr → P r ) is 1.38 ± 0.06.