Evidence for Binding of Phytochrome to Membranes
Whether phytochrome can act as a membrane effector in photomorphogenesis is still controversial. Recently phytochrome-mediated threshold responses have been observed which imply significant cooperativity of the primary reaction, Pfr + X →PfrX (OELZE and MOHR, 1973; SCHOPFER and OELZE-KAROW, 1971). But it has also been found that, in the same organ (mustard cotyledons), the primary reaction of Pfr does not involve any significant cooperativity in the case of phytochrome-mediated anthocyanin synthesis (DRUMM and MOHR, 1974). This indicates that the concept of a common initial reaction of Pfr can hardly be maintained. It was furthermore concluded by DRUMM and MOHR (1974) that in phytochrome-mediated anthocyanin synthesis a phytochrome (Pfr) induced change in the reaction matrix occurs. However the actual threshold value was not obviously affected by different Pfr concentrations (OELZE and MOHR, 1973). Against the background of these physiological data new results on phytochrome membrane interactions will be discussed.
KeywordsPrimary Reaction Equilibrium Binding Constant Photostationary State Significant Cooperativity Corn Coleoptile
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