Secondary metabolites tissue

Application of Preparative Layer Chromatography for the Separation of Secondary Metabolites from Plant Tissues... 

In 1992, Paul and Van Alstyne reported on the processes that occur after tissue disruption in different species of the calcified green seaweed Halimeda [56]. After wounding, these algae transform their major secondary metabolite, the his-enoylacetate diterpene halimedatetraacetate (48), into halimedatrial (50) and epihalimedatrial (51). The structural relationship between the educt and the reaction products suggests that the transformation occurs by a combination of solvolysis and hydrolysis reactions as indicated in Scheme 14 [108]. 

Marine hydroids are commonly defended from predation by nematocysts that are capable of penetrating the tissue of predators, and injecting proteinaceous venom. However, lipophilic secondary metabolites also protect many hydroid species. The hydroid Tridentata marginata is chemically defended by tridentatols A-D (85-88), of which tridentatol A (85) is a potent deterrent to fish predation (Scheme 22) [160]. 

The presence in molluscs of molecules structurally related to typical dietary metabolites could be ascribed either to selective accumulation of minor compounds acquired through the diet, or to an in vivo chemical transformation of major metabolites acquired from the prey. However, all reports on this topic have to be carefully evaluated before drawing hurried conclusions. In particular, interaction among molecules from different organs could favor formation of artifacts when the secondary metabolites are extracted from the whole mollusc and not from individual dissected tissues. Only some cases, where the ability of the molluscs to modify dietary metabolites seems to be well supported, are reported in this chapter. 

Expressed sequence tag (EST) analysis of cDNAs from specific plant tissues has proved to be a valuable tool for the identification of genes for secondary metabolite biosynthesis.36 We have used this approach to identify two distinct sequences predicted to encode OSCs from cDNA libraries from roots of diploid oat (Avena strigosa).35 One of these sequences is highly homologous to cycloartenol... 

Since 1988, the methods that we use to isolate cDNAs of alkaloid biosynthesis have become ever more facile and sensitive, allowing for more efficient cDNA identification. We do not, however, yet understand enough about the cellular localization of alkaloid formation or about the nature of the catalysts to move completely away from enzymology and biochemistry and to use only molecular genetic techniques to dissect these biosynthetic pathways. Even our most recently successful cDNA isolations and identifications involved classical protein purification. We are beginning now to use proteomics and EST sequencing to identify natural product biosynthetic cDNAs, but these approaches are more feasible when a specialized cell/tissue type in which secondary metabolite biosynthetic pathways are active, can be isolated and used as a protein or RNA source. 

Allelopathy is defined as biochemical interactions between one plant or microorganism (alga, bacteria, or virus) and another plant through the production of chemical compounds - secondary metabolites (allelochemicals), which influence, direct or indirect, harmful or beneficial, plant growth and development (Rice 1984). Allelochemicals are present in almost all plants and in many tissues, like leaves, stems, flowers, fruits, seeds, roots, or pollen and may be released from plants into the environment by volatilization, leaching, root exudation, and decomposition of plant residues (Chou 1990). 

Studies that address the site of production, the transport, and the deposition of secondary metabolites provide another level of resolution that needs to be considered when evaluating the function of secondary metabolites and their patterns of distribution. Unlike approaches that quantify an alga s total metabolite concentration, studies that localize metabolites contained within algal tissues provide evidence of more subtle changes in metabolite distribution in response to stimuli and may clarify metabolite function. 

About 120 chemical constituents have been identified in chamomile as secondary metabolites, including 28 terpenoids, 36 flavonoids and 52 additional compounds [4]. A substantial part of drag effects are determined by the essential oil content. Oil is collected from flower heads, either by steam distillation or solvent extraction, for yields of 0.24-1.90% of fresh or dry plant tissue. Among the essential oil constituents the most active are /-/-a-bisabolol and chamazulene. /-/-a-bisabolol has demonstrated anti-inflammatory, antispasmodic, antimicrobial, antiulcer, sedative and CNS activity. Chamazulene is also anti-inflammatory. Topical applications of chamomile preparation have shown benefit in the treatment of eczema, dermatitis and ulceration [5]. 

Mulabagal V, Lee C-Y, Lo S-F, Nalawade SM, Lin, C-Y, Tsay H-S. (2004) Studies on the production of some important secondary metabolites from medicinal plants by plant tissue cultures. Bot Bull Acad Sinica (Taiwan) 45 1-22. 

Phase I renders xenobiotics more polar. Oxidation is the most important process of phase I. It is carried out in the endoplasmic reticulum in many tissues by monooxygenases that contain cytochrome P450 (P450-dependent mixed function oxidases) as electron carrier. These enzymes have evolved in the past billion years in response to plant secondary metabolites. There are a number of P450 gene families. 

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