Secondary Metabolism and Cell Differentiation

1. Secondary Metabolism and Differentiation In addition to the primary metabolic reactions, which are similar in all living beings (formation and breakdown of nucleic acids and proteins as well as of their precursors, of most carbohy­ drates, of some carboxylic acids, etc. ), a vast number of metab­ olic pathways lead to the formation of compounds peculiar to a few species or even to a single chemical race only. These reac­ tions, in accord with CZAPEK (1921) and PAECH (1950), are summed up under the term "secondary metabolism", and their products are called "secondary metabolites. " The wide variety of secondary products formed in nature includes such well-known groups as alkaloids, antibiotics, cardiac glyco­ sides, tannins, saponins, volatile oils, and others. A consider­ able number of them are of economic importance in therapeutics or technology. Although secondary products are produced by micro­ organisms, higher plants, and animals (cf. LUCKNER, 1972), most of the substances are found in the plant kingdom. The lack of mechanisms for true excretion in higher plants may result in this unequal distribution, the "waste products" of metabolism in plants instead being accumulated in the vacuoles, the cell walls, or in special excretory cells or spaces of the organism ("metabolic excretion," cf. FREY-WYSSLING, 1935, 1970; MOTHES, 1966a, b, 1972; LUCKNER et al. , 1976. Many secondary substances have, however, a direct biologic func­ tion. They can be regulatory effectors, e. g.

Contenu

I. Expression of Secondary Metabolism, An Aspect of Cell Specialization of Microorganisms, Higher Plants, and Animals.- A. Introduction.- 1. Secondary Metabolism and Differentiation.- 2. Investigation of the Molecular Biology of Differentiation.- B. Coordinate and Noncoordinate Formation of Enzymes of Secondary Metabolism.- C. Regulatory Effectors of Secondary Metabolism.- 1. The Influence of Tryptophan and Tryptophan Analogs on the Expression of Ergolin Alkaloid Biosynthesis in Clavieeps Species.- 2. Stimulation of Streptomycin Formation in Actinomyces strep tony cini by the A-Factor.- 3. The Effect of Cinnamic Acids on Anthocyanin Synthesis in Petunia hybrida.- 4. The Influence of the Light-Phytochrome System on the Regulation of Phenylpropanoid Metabolism in Higher Plants.- 5. The Action of Adrenocorticotrophic Hormone on Corticosteroid Formation in the Adrenal Cortex.- D. Phase Dependence of Secondary Metabolism and the Organization of Differentiation Programs.- 1. Integration of Alkaloid Metabolism into the Developmental Program of Penioillium cyelopium.- a) Growth, Conidia, and Alkaloid Formation.- b) Formation of the Enzymes of Alkaloid Metabolism during Conidiation.- c) Influence of Inhibitors of Gene Expression on Hyphal Cyclopenin-Cyclopenol Formation.- d) Glucose as Repressor of Idiophase Development.- e) The Developmental Program of Penicillium eyelopium.- 2. Biosynthesis of Secondary Products during Bacterial Sporulation.- 3. Sequential Gene Expression in Secondary Metabolism of Penieillium urtieae?.- 4. Sequential Formation of Secondary Products during the Generative Development of Mucoraceous Fungi.- 5. Expression of Secondary Metabolism in Developing Chloroplasts.- 6. Secondary Product Formation during Microsporogenesis in Higher Plants.- 7. Induction of Urea Cycle Enzymes as Part of the Thyroid Hormone-Stimulated Metamorphosis of Rana eatesbeiana Tadpoles.- 8. The Formation of Tanning Agents during Ecdysone-Controlled Pupation of Calliphova Larvae.- E. Conclusions.- References.- II. Secondary Metabolism in Cell Cultures of Higher Plants and Problems of Differentiation..- A. Introduction.- B. The Fate of Secondary Metabolism during Initiation of Plant Cell Cultures.- C. Realization of Secondary Metabolism in Plant Cell Cultures.- 1. Triggering Factors.- 2. Enzyme Activities.- 3. Comparison with the Related Intact Plant.- D. Correlation between Secondary Metabolism and Cellular Structures.- E. Growth of Plant Cell Cultures and Formation of Secondary Substances.- F. Concluding Remarks.- References.