In the growth condition(s) of plants, numerous secondary metabolites (SMs) are produced by them to serve variety of cellular functions essential for physiological processes, and recent increasing evidences have implicated stress and defense response signaling in their production. The type and concentration(s) of secondary molecule(s) produced by a plant are determined by the species, genotype, physiology, developmental stage and environmental factors during growth. This suggests the physiological adaptive responses employed by various plant taxonomic groups in coping with the stress and defensive stimuli. The past recent decades had witnessed renewed interest to study abiotic factors that influence secondary metabolism during in vitro and in vivo growth of plants. Application of molecular biology tools and techniques are facilitating understanding the signaling processes and pathways involved in the SMs production at subcellular, cellular, organ and whole plant systems during in vivo and in vitro growth, with application in metabolic engineering of biosynthetic pathways intermediates.

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Stress and defense responses in plant secondary metabolites production

Plant in vitro culture for the production of antioxidants : A review

Plant in vitro culture for the production of antioxidants

Plant aromatic L-amino acid decarboxylases: evolution, biochemistry, regulation, and metabolic engineering applications

The present review focuses on the various Ocimum species, often referred to as the “king of the herbs.” The botany of more than 50 species of herbs and shrubs belonging to this genus is thoroughly reported, along with traditional uses and cultivation techniques. Since basil is a rich source of natural compounds, details on the several chemical constituents of essential oil, plant parts and derived food and medical products, such as monoterpenes, sesquiterpenes, phenylpropanoids, anthocyanins, and phenolic acids, as well as their effect on sensory qualities are included. Furthermore, particular emphasis is given to the application of biotechnology for the clonal micropropagation of basil lines with improved traits and the use of basil tissue culture for the derivation of valuable compounds, such as antioxidant phenolics and essential oil components.

Ocimum sp. (Basil): Botany, Cultivation, Pharmaceutical Properties, and Biotechnology

Rosmarinic acid, or α-0-caffeoyl-3,4-dihydroxyphenyllactic acid (Fig. 1), is a representative of a major class of plant secondary metabolites, the ester- or amide-linked conjugates of hydroxycinnamic acids. These compounds, along with the flavonoid tannins, are believed to serve as the substrates for peroxidases and polyphenol oxidases during the browning of damaged plant tissues and the hypersensitive response to pathogen attack (Tomiyama et al. 1967). Auto-oxidation and enzymic oxidation convert the hydroxycinnamoyl moiety to various reactive species which can readily couple covalently with electron-deficient centers in proteins, nucleic acids and other metabolites (Pierpoint et al. 1977; Igarashi and Yasui 1985). Since this process can rapidly destroy the functional integrity of a cell, hydroxycinnamoyl conjugates in living cells must normally be sequestered in a cellular compartment which isolates them from oxidative enzyme catalysis. The limited evidence on this point indicates that the soluble conjugates are normally stored within the central vacuole (Chaprin and Ellis 1984). There is also a pool of insoluble conjugates associated with the cell wall (El-Basyouni et al. 1964), but their metabolic relationship to the soluble conjugates remains unknown.

Rosmarinic acid production in Coleus cell cultures.

Tyrosine decarboxylase (EC 4.1.1.25) from Syringa vulgaris L. cell cultures and from Hordeum vulgare L. seedlings is strongly inhibited by the phenylalanine analogue, l-α-aminooxy-β-phenylpropionate. l-α-Aminooxy-β-phenylpropionate is therefore not specific in its inhibitory action against phenylalanine ammonia-lyase (EC 4.3.1.5). Hordeum tyrosine decarboxylase is also very sensitive to α-fluoromethyl(3,4-dihydroxyphenyl)alanine, but preparations from Nicotiana tabacum L. and Sanguinaria canadensis L. are largely unaffected by either type of inhibitor.

Plant tyrosine decarboxylase can be strongly inhibited by L-α-aminooxy-β-phenylpropionate.

Phenylalanine ammonia-lyase from an "over-producer" strain of Coleus blumei Benth. cell cultures accumulating high levels of rosmarinic acid (RA) has been shown to possess no special feed-back sensitivity to RA or its precursors. No tyrosine-3-hydroxylase activity could be detected in culture extracts and no specific inhibitors of tyrosine incorporation into RA were found. L-α-aminooxy-β-phenyl propionic acid, however, was effective in specifically blocking phenylalanine incorporation. This block also led to an accumulation of label from tyrosine in 4-hydroxyphenyllactic acid rather than in 3,4-dihydroxyphenylalanine (DOPA) or 3,4-dihydroxyphenyllactic acid. These observations require a re-evaluation of the possible role of DOPA as a major biogenic precursor to RA.

B. E. Ellis

Papers

Rosmarinic acid production in Coleus cell cultures.

Plant tyrosine decarboxylase can be strongly inhibited by L-α-aminooxy-β-phenylpropionate.

Interactions between parallel pathways during biosynthesis of rosmarinic acid in cell suspension cultures of Coleus blumei