Natural products plant hormones

Steroids, compounds with a cyclopenta[a]phenanthrene skeleton (15), include a wide range of natural products such as sterols (e.g., cholesterol), sex hormones, adrenocorticoid hormones, cardiac glycosides and vitamin D [31]. Sterols are steroids having a hydroxyl group at position 3 of the basic skeleton. Steroids can be found both in plants and in animals. 

Throughout history, mankind has always been interested in naturally occurring compounds from prebiotic, microbial, plants and animals sources. Various extracts of flowers, plants and insects have been used for isolating compounds whose task, color and odor could be used for various purposes. Many natural products, such as plant hormones, have a regulatory role, while others function as chemical defense against pests. The role of certain compounds is to act as chemical messengers, such as sex-attractants (pheromones) in insects, terrestrial and marine animals and humans. What is the origin of natural products ... 

It was only recently that the presence and significance of the sano, or structurally closely related, natural products on land and in the sea has received specific attention (Pietra 1995). Three main conclusions were arrived at (a) the highest fiequency of structural similarities for secondary metabolites occurs with terpenoids fi om anthozoans and land plants (b) biosynthetic routes became adapted to the fimction of the metabolite, such as a defensive one that must persist, or a hormonal one that needs to be rapidly switched off, so, the synthesis of the same compoimd in phylogeneticalfy close organisms should occur by the same pathway, while different biosynthetic routes should be used by phylogenetically distant organisms, and (c) the contribution of marine bacteria to the genes for secondary metabolites in eukaryotes was scarce (Pietra 1995). 

Pearce, G. Moura, D.S. Stratmann, J. Ryan, C.A. (2001) Production of multiple plant hormones from a single polyprotein precursor. Nature, 411, 817-20. 

Enzymes that directly incorporate molecular oxygen into organic substrates play a crucial role in many fundamental biological processes such as degradation of natural products in the biosphere, biosynthesis and metabolism of amino acids, hormones, drugs, etc. A wide variety of enzymic oxygenases has been identified and isolated from microorganisms, plants and animals. A detailed description of these enzymes is beyond the scope of this chapter, but several books and review articles are available.1,58-62... 

Terpenes are natural products usually obtained from the essential oils of plants. They contain multiples of five-carbon atoms (5, 10, 15, and so on). Each five-carbon arrangement is called an isoprene unit, a four-carbon chain with a one-carbon branch at C-2. Terpenes are frequently used in fragrances and perfumes. Steroids are lipids that contain a unique four-ring structure and are biosynthetically related to terpenes. Important examples of steroids include cholesterol, the bile acids, and the sex hormones. 

The simplest unsaturated carbon compound, ethylene, exerts a major influence on many if not all aspects of plant growth and development. Although ethylene is a gas at physiological temperatures and pressures, it is now recognized as a plant hormone because it is a natural product of metabolism, acts in trace amounts and is neither a substrate nor cofactor in reactions which are associated with major developmental plant processes. Whether or not ethylene meets all the standard criteria established for hormones, there is no question that this gas is a powerful natural regulating substance in plant metabolism, and that it acts and interacts with other recognized plant hormones. With the advent of gas chromatography, ethylene has become the simplest plant hormone to assay since it is evolved from the tissues and requires no extraction or purification prior to analysis. 

Interestingly, several natural products, besides their role as antibiotics and phytotoxins, exhibit plant growth responses (mainly inhibition). In order to keep their identity as such, these were listed under miscellaneous natural products (Table 1). Furthermore, compounds which have structural features similar to those present in hormones (gibberellins and ABA.) and which exhibit similar growth responses are also listed under miscellaneous natural products (Table 1). 

Francke W. and Schulz S. (1999) Pheromones. In Natural Products, Vol. 8 (Including Marine Natural Products, Pheromones, Plant Hormones and Aspects of Ecology, eds D. Barton, K. Nakanishi, and O. Meth-Cohn, pp. 197-261. Elsevier Science Ltd, Oxford. 

But chrysanthemic acid derivatives are by far not the only examples of cyclopropane-containing structures in nature. In fact, the highly strained three-membered carbocycle is virtually ubiquitous. It occurs, for example, in every green plant in the form of 1-aminocyclopropanecarboxylic acid (ACC) 2, a direct precursor to the plant hormone ethylene [3]. In addition, the cyclopropane unit is found in a variety of other natural products, inter alia in terpenes and in various cyclopropanated fatty acids [4]. The biochemical precursors of the latter are unsaturated fatty acids, and in view of the existence of polyunsaturated fatty... 

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