Experiments Regarding the Problem of Differentiation in Multicellular Systems

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Abstract
The temporal pattern of control by phytochrome of the enzyme lipoxygenase (EC 1.13.1.13) in the mustard seedling (Sinapis alba L.) is described. The biosynthetic system which produces lipoxygenase does not respond to phytochrome (Pfr) up to 33.25 h after sowing (25°C). By this time the control by Pfr comes suddenly and fully into play. At 48 h after sowing the system escapes from the control by Pfr. Neither the beginning nor the end of the period of control is influenced by phytochrome. Interpretation of the data requires a double action control mechanism. It is argued that such a mechanism is necessarily a characteristic of development in multicellular organism.