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Salicylic Acid Synthesis | |
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Salicylic acid induces
flowering, inhibits K+ and P+ uptake, and inhibits ethylene
synthesis. It is probably antagonistic to jasmonic acid. SA
triggers the systemic acquired response (SAR) and may move as a
long-distance component of a signal transduction pathway. SA induces the
pathogenesis related proteins PR-1, PR-2, PR-5, beta-1,3-glucanase, and
glutathione S-transferase. SA participates in SAR and in the localized
hypersensitive response (HR). It induces alternative pathway
respiration.
Two alternative pathways for SA synthesis have been proposed. One pathway would convert chorismate via isochorismate synthase and pyruvate lyase to SA (Wildermunt). In the other pathway (Klessig) phenylalanine is converted by PAL and BA-2-hydroxylase into SA. Other reactions using SA and derivatives use UDP-glucose:SA glucosyltransferase, and SA-B-glucosidase for interconversion of SA derivatives.
SA elevates H2O2 levels and binds and inhibits catalase,
which degrades H2O2, which, in turn, induces PR-1
(pathogenesis related protein-1). SA also inhibits ascorbate peroxidase,
which also scavenges H2O2, but does not inhibit peroxidases
involve in lignification and cell wall cross-linking (Klessig). SA
inhibits ACC synthase, reducing ethylene production, and aconitase. PR-1 and PR-5 have activity against oomycetes; chitinases have anti fungal activity.
Refs: Wildermunt, M.C., J. Dewdne, G. Wu, A.M. Ausubel. 2001. Nature 414:562-565 Klessig, D.F, J. Durner, J. Shah, Y. Yang. 1998. Phytochemical Signals and Plant Microbe Interactions, ed. Romeo et al. Ch. 7. Plenum Press, NY. pp.119-137 Verberne et al. 2000. Nature Biotech 18:779-783
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