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PHYTOCHROME INTERMEDIATES IN VIVO—IV. KINETICS OF P fr EMERGENCE*
Author(s) -
Spruit C. J. P.
Publication year - 1982
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.1751-1097.1982.tb03818.x
Subject(s) - arrhenius equation , reaction rate constant , phytochrome , epicotyl , kinetics , activation energy , chemistry , oxygen , atmosphere (unit) , photochemistry , analytical chemistry (journal) , thermodynamics , botany , biology , physics , organic chemistry , quantum mechanics , red light , seedling
— Rate constants for the formation of P fr , the far‐red‐absorbing form of phytochrome, from photochemical intermediates, have been measured in vivo in a number of plants. Two first order processes were observed, the slowest of which has been studied in detail. In pea epicotyl hooks, the rate constants proved dependent on temperature as well as on composition of the gas phase. A transition point was observed at about—2°C. Above this temperature the Arrhenius activation energy is 61 ± 6 kJ/mol, below the transition temperature 200 + 17 kJ/mol. The data correspond to half lives of between 0.4 and 0.2 s in an atmosphere of oxygen at 20°C, depending upon the species of plant. In oxygen‐free atmospheres, the rates are between 1.7 and 1.9 times as fast. The data prove that, on the time scale relevant to the usual type of photomorphogenetic experiments, the occurrence of phytochrome intermediates generally can be neglected. Exceptions to this generality are formed by experiments involving continuous or very rapidly intermittent exposures to very high light intensities. Under these conditions the steady state fraction of P fr may be considerably lower than calculated from the spectroscopic data for the pigment and the light sources.