Phenylpropanoid compounds encompass a wide range of structural classes and biological functions. Limiting discussion to stress-induced phenylpropanoids eliminates few of the structural classes, because many compounds thst are constitutive in one plant species or tissue can be induced by various stresses in another species or in another tissue of the same plant (Beggs et al., 1987; Christie et al., 1994).

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Stress-Induced Phenylpropanoid Metabolism.

The antioxidative activity of a total of 92 phenolic extracts from edible and nonedible plant materials (berries, fruits, vegetables, herbs, cereals, tree materials, plant sprouts, and seeds) was examined by autoxidation of methyl linoleate. The content of total phenolics in the extracts was determined spectrometrically according to the Folin-Ciocalteu procedure and calculated as gallic acid equivalents (GAE). Among edible plant materials, remarkable high antioxidant activity and high total phenolic content (GAE > 20 mg/g) were found in berries, especially aronia and crowberry. Apple extracts (two varieties) showed also strong antioxidant activity even though the total phenolic contents were low (GAE < 12.1 mg/g). Among nonedible plant materials, high activities were found in tree materials, especially in willow bark, spruce needles, pine bark and cork, and birch phloem, and in some medicinal plants including heather, bog-rosemary, willow herb, and meadowsweet. In addition, potato peel and beetroot peel extracts showed strong antioxidant effects. To utilize these significant sources of natural antioxidants, further characterization of the phenolic composition is needed.

Antioxidant activity of plant extracts containing phenolic compounds

/pdf/purification-and-characterization-2y44lhntkf.pdf

Purification and Characterization

The chemical diversity and distribution of glucosinolates and isothiocyanates among plants

The biochemistry and medical significance of the flavonoids.

https://digital.library.unt.edu/ark:/67531/metadc488146/m2/1/high_res_d/2003_phytochemistry_815.pdf

Phytochemistry meets genome analysis, and beyond.

Colonization of barley (Hordeum vulgare cv Salome) roots by an arbuscular mycorrhizal fungus, Glomus intraradices Schenck & Smith, leads to elevated levels of endogenous jasmonic acid (JA) and its amino acid conjugate JA-isoleucine, whereas the level of the JA precursor, oxophytodienoic acid, remains constant. The rise in jasmonates is accompanied by the expression of genes coding for an enzyme of JA biosynthesis (allene oxide synthase) and of a jasmonate-induced protein (JIP23). In situ hybridization and immunocytochemical analysis revealed that expression of these genes occurred cell specifically within arbuscule-containing root cortex cells. The concomitant gene expression indicates that jasmonates are generated and act within arbuscule-containing cells. By use of a near-synchronous mycorrhization, analysis of temporal expression patterns showed the occurrence of transcript accumulation 4 to 6 d after the appearance of the first arbuscules. This suggests that the endogenous rise in jasmonates might be related to the fully established symbiosis rather than to the recognition of interacting partners or to the onset of interaction. Because the plant supplies the fungus with carbohydrates, a model is proposed in which the induction of JA biosynthesis in colonized roots is linked to the stronger sink function of mycorrhizal roots compared with nonmycorrhizal roots.

Induction of Jasmonate Biosynthesis in Arbuscular Mycorrhizal Barley Roots

The repertoire of secondary metabolism (involving the production of compounds not essential for growth) in the plant kingdom is enormous, but the genetic and functional basis for this diversity is hard to analyse as many of the biosynthetic enzymes are unknown We have now identified a key enzyme in the ornamental plant Gerbera hybrida (Asteraceae) that participates in the biosynthesis of compounds that contribute to insect and pathogen resistance Plants transformed with an antisense construct of gchs2, a complementary DNA encoding a previously unknown function1,2, completely lack the pyrone derivatives gerberin and parasorboside The recombinant plant protein catalyses the principal reaction in the biosynthesis of these derivatives: GCHS2 is a polyketide synthase that uses acetyl-CoA and two condensation reactions with malonyl-CoA to form the pyrone backbone of thenatural products The enzyme also accepts benzoyl-CoA to synthesize the backbone of substances that have become of interest as inhibitors of the HIV-1 protease3,4,5 GCHS2 is related to chalcone synthase (CHS) and its properties define a new class of function in the protein superfamily It appears that CHS-related enzymes are involved in the biosynthesis of a much larger range of plant products than was previously realized

New pathway to polyketides in plants

Antioxidant flavonoids from leaves of Polygonum hydropiper L.

Experiments were performed to confirm that the aldimine bond formation is a spontaneous reaction, because attempts to find an enzyme catalyzing the last decisive step in betaxanthin biosynthesis, the aldimine formation, failed. Feeding different amino acids to betalain-forming hairy root cultures of yellow beet ( Beta vulgaris L. subsp. vulgaris “Golden Beet”) showed that all amino acids ( S - and R -forms) led to the corresponding betaxanthins. We observed neither an amino acid specificity nor a stereoselectivity in this process. In addition, increasing the endogenous phenylalanine (Phe) level by feeding the Phe ammonia-lyase inhibitor 2-aminoindan 2-phosphonic acid yielded the Phe-derived betaxanthin. Feeding amino acids or 2-aminoindan 2-phosphonic acid to hypocotyls of fodder beet ( B. vulgaris L. subsp. vulgaris “Altamo”) plants led to the same results. Furthermore, feeding cyclo -3-(3,4-dihydroxyphenyl)-alanine ( cyclo -Dopa) to these hypocotyls resulted in betanidin formation, indicating that the decisive step in betacyanin formation proceeds spontaneously. Finally, feeding betalamic acid to broad bean ( Vicia faba L.) seedlings, which are known to accumulate high levels of Dopa but do not synthesize betaxanthins, resulted in the formation of dopaxanthin. These results indicate that the condensation of betalamic acid with amino acids (possibly including cyclo -Dopa or amines) in planta is a spontaneous, not an enzyme-catalyzed reaction.

Dieter Strack

Papers

Phytochemistry meets genome analysis, and beyond.

Induction of Jasmonate Biosynthesis in Arbuscular Mycorrhizal Barley Roots

New pathway to polyketides in plants

Antioxidant flavonoids from leaves of Polygonum hydropiper L.

The decisive step in betaxanthin biosynthesis is a spontaneous reaction1