Phytochrome: First-order phototransformation kinetics in vivo.
The deviation from first order commonly observed in phototransformation kinetics of phytochrome in vivo is due to a light-intensity gradient within the sample. This gradient was measured and was found to approach that predicted by the Kubelka-Munk theory of light scatter in turbid materials. The influence of this gradient is eliminated and first-order phototransformation kinetics are obtained, when either (i) thin samples of translucent (low optical density) material of high phytochrome content are measured directly; or (ii) thin samples of opaque (high optical density) or translucent material are sandwiched between two layers of light-scattering material. This result is consistent with the existence of only one population of photoreversible phytochrome molecules in vivo.
Institute für Biologie III und II der Universität Freiburg, Schänzlestraße 9-11, D-7800, Freiburg i. Br., Federal Republic of Germany.
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W
Schmidt
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D
Marmé
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P
Quail
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Schäfer