Coordinated enzyme expression

Phases of susceptibility in which secondary metabolism is influenced by appropriate signals have also been detected in higher plants. The induction of antho-cyanin biosynthesis (D 22.3.3) by phytochrome in the epidermal cells of the cotyledons of Sinapis alba for instance, first begins 27 h after sowing, despite the fact that the phytochrome system per se is fully functional immediately after sowing. Competence with respect to anthocyanin formation is determined endogenously, i.e., by the state of differentiation of the epidermis cells in which the anthocyanins are formed and accumulated. 

Luckner, M. Expression and control of secondary metabolism In Encyclopedia of Plant Physiology, New Series, Vol. 8, Secondary Plant Products (E. A. Bell, B. V. Charlwood, eds.), pp. 23-63. Springer, Berlin-Heidelberg-New York 1980 Nover, L., Luckner, M., Parthier, B. (eds.) Cell Differentiation. Fischer/Springer, Jena/Berlin-Heidelberg-New York 1982 

Coordinated regulation of the activity of enzymes of one biosynthetic pathway seems to occur frequently in secondary metabolism (see, e.g.. Figs. 7 and 8). It has been examined in detail in the flavonoid metabolism of higher plants. 

In the plant itself, however, another pattern of control is established. In cotyledons and leaves of Petroselinum hortense seedlings the regulatory behavior of PAL and several group II enzymes 

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Ethylene coordinates the expression of genes responsible for enhanced respiratory metabolism, chlorophyll degradation, carotenoid synthesis, conversion of starch to sugars, increased activity of cell wall-degrading enzymes, aroma volatile production, and so on. All these events stimulate a series of biochemical, physiological, and structural changes making fruits mature and attractive to the consumer. 

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