On the phytochrome phototransformation kinetics in mustard seedlings

The in vivo phototransformation kinetics of mustard hook and cotyledon phytochrome exhibit a deviation from a single first order curve, quite similar to that for pumpkin hooks as reported in a previous paper (Boisard, Marmé and Schäfer, 1971). The P fr→Prkinetics can be characterized by the ratios ɛ fr,λ (I) · P fr (I) /ɛ fr,λ (II) · P fr,λ (II) and [Formula: see text] where P fr (I) and P fr (II) are two populations of phytochrome molecules which convert to P rwith a first order half-life of [Formula: see text] and [Formula: see text]. These ratios depend on the length of time of etiolation. The ratio ɛ fr,λ (I) · P fr (I) /ɛ fr,λ (II) · P fr,λ (II) is independent of the amount of total P frpresent at the beginning of the P fr→Prphototransformation after a non-saturating dose of red light. The half-lives of the two populations, however, depend on the concentration of total P frinitially present. P fr→Prphototransformation kinetics with different light intensities show that reciprocity holds.