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10. Antioxidant Mechanisms of Polyphenolic Caffeic Acid Oligomers, Constituents of Salvia officinalis

Author

BORS,WOLF, CHRISTA,MICHEL, STETTMAIER,KURT, YINRONG,LU, L. YEAP,FOO, BORS,WOLF, CHRISTA,MICHEL, STETTMAIER,KURT, YINRONG,LU, and L. YEAP,FOO

Abstract

Caffeic acid, rosmarinic acid and oligomers of caffeic acid with multiple catechol groups are all constituents of Salvia officinalis. Their antioxidant potential was investigated with regard to their radical scavenging activity and the stability and structure of the intermediate radicals. Pulse-radiolytic studies revealed very high rate constants with hydroxyl radicals. Evidence from kinetic modeling calculations suggested an unusual complex behavior due to the presence of both O4- and O3-semiquinones and formation and decay of a hydroxyl radical adduct at the vinyl side chain. The radical structures observed by EPR spectroscopy after autoxidation in slightly alkaline solutions were only partially identified due to their instability and generally represented dissociated O4-semiquinones. Hybrid density-functional calculations of the potential radical structures showed distinct differences between the resonance stabilization of the O4- and O3-semiquinones of caffeic and dihydrocaffeic acids, reflected also in the considerably faster decay of the O3-semiquinone observed by pulse radiolysis. No evidence was found for dimerization reactions via Cb radicals typical for lignin biosynthesis

Published
2004

25. Nitric oxide is induced by wounding and influences jasmonic acid signaling in Arabidopsis thaliana.

Author

Xi Huang, Stettmaier, Kurt, Michel, Christa, Hutzler, Peter, Mueller, Martin J., and Durner, Jörg

Subjects
NITRIC oxide, ARABIDOPSIS thaliana, PLANT defenses, PLANT ecology, CELL death, PLANT cells & tissues
Abstract

Nitric oxide (NO) has been associated with plant defense responses during microbial attack, and with induction and/or regulation of programmed cell death. Here, we addressed whether NO participates in wound responses in Arabidopsis thaliana (L.) Heynh.. Real-time imaging by confocal laser-scanning microscopy in conjunction with the NO-selective fluorescence indicator 4,5-diaminofluorescein diacetate (DAF-2 DA) uncovered a strong NO burst after wounding or after treatment with JA. The NO burst was triggered within minutes, reminiscent of the oxidative burst during hypersensitive responses. Furthermore, we were able to detect NO in plants (here induced by wounding) by means of electron paramagnetic resonance measurements using diethyldithiocarbamate as a spin trap. When plants were treated with NO, Northern analyses revealed that NO strongly induces key enzymes of jasmonic acid (JA) biosynthesis such as allene oxide synthase (AOS) and lipoxygenase (LOX2). On the other hand, wound-induced AOS gene expression was independent of NO. Furthermore, JA-responsive genes such as defensin (PDF1.2) were not induced, and NO induction of JA-biosynthesis enzymes did not result in elevated levels of JA. However, treatment with NO resulted in accumulation of salicylic acid (SA). In transgenic NahG plants (impaired in SA accumulation and/or signaling), NO did induce JA production and expression of JA-responsive genes. Altogether, the presented data demonstrate that wounding in Arabidopsis induces a fast accumulation of NO, and that NO may be involved in JA-associated defense responses and adjustments. [ABSTRACT FROM AUTHOR]

Published
2004
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28. Methoxyphenols—antioxidant principles in food plants and spices: Pulse radiolysis, EPR spectroscopy, and density functional theory calculations<FNR HREF="fn1">*</FNR> <FN ID="fn1"> This article was presented in part as a poster (Abstract, p. 7) at the MathChemComp2000 conference in Dubrovnik, Croatia, June 19–24, 2000. </FN>

Author

Bors, Wolf, Kazazic, Snjezana P., Michel, Christa, Kortenska, Vessela D., Stettmaier, Kurt, and Klasinc, Leo

Abstract

The phenoxyl radicals of several phenols and phenolic acids with o-methoxy groups were generated by pulse-radiolytic oxidation with azide radicals and their buildup and decay evaluated with kinetic spectroscopy. Structures of the phenoxyl radicals were obtained with EPR spectroscopy and the experimental isotropic coupling constants confirmed by hybrid density-functional calculations with Becke's three parameter hybrid functional using the Lee, Yang, and Parr functional theory and a variety of basis sets, and with consideration of the solvent. While the calculations resulted in reasonable correlations with the experimental data, the apparent distinction in the stability of the various radicals seems to be primarily due to kinetic rather than electronic effects. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem, 2002

Published
2002
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