Temperature dependence of phytochrome dark reactions.

The dark reversion and the destruction reaction of the phytochrome of squash (Cucurbita pepo L.) cotyledons show different temperature behaviour in the temperature range 15-35°. The Arrhenius activation energy of the destruction reaction is temperature independent whereas that of the reversion reaction shows a jump at 20°. This indicates an interaction of phytochrome molecules with membranes. A reaction scheme is discussed which can explain the differences of the dark kinetics in a quantitative manner.