STABILIZATION OF PHYTOCHROME INTERMEDIATES BY LOW TEMPERATURE*

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Abstract
Abstract— The photocon versions between the red‐absorbing form (Pr) and the far‐red absorbing form (Pfr) of phytochrome were examined at low temperatures. Partially purified preparations of the chromoprotein were examined in phosphate buffer and in 25 per cent buffer plus 75 per cent glycerol. Actinic irradiation of P, below – 150°C produces an intermediate with maximum absorbance near 695 nm, R695. Actinic irradiation of R695 converts it back to P. Above – 150°C R695 decays to a low extinction form of phytochrome, R, which in turn decays to Pfr upon further warming. Light absorption by Pfr below – 150°C results in the formation of an intermediate form of phytochrome with maximum absorbance near 660 nm, FR660. FR660 decays upon warming to a lower extinction form, FR'. which in turn decays to Pr on continued warming. No evidence was obtained to suggest that any of the observed intermediate states are involved in more than one direction of phytochrome photocon version.

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