Transport of Salicylic Acid and Related Compounds

Various stresses promote SA accumulation. SA is in part conjugated in the cytoplasm to inactive compounds such as salicylic acid O-β-glucoside (SAG) or modified to active compounds such as methylsalicylate (MeSA). SAG is sequestered in the vacuole by an A

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Transport of Salicylic Acid and Related Compounds J.-L. Bonnemain, J.-F. Chollet and F. Rocher

Abstract Various stresses promote SA accumulation. SA is in part conjugated in the cytoplasm to inactive compounds such as salicylic acid O-b-glucoside (SAG) or modified to active compounds such as methylsalicylate (MeSA). SAG is sequestered in the vacuole by an ATP-binding cassette transporter mechanism or an H+-antiporter mechanism. Free SA is mobile and can be transported within the plant, mainly via the phloem. SA molecules found in the phloem sap may come from the synthesis area via the symplastic route in symplastic loaders or may be taken up from the phloem apoplast (apoplastic loaders). In this latter case, SA must cross the plasma membrane of the companion cell-sieve cell complex. Similarly, synthetic derivatives or analogs applied to the foliage to enhance plant defence must cross at least once the plasma membrane before reaching the sieve tubes. The ability of molecules to diffuse through the plasma membrane is dependent on their chemical properties (size of the molecule, Log D, polar surface area, number of hydrogen bond donors). On these bases, the discrepancies between the computed predictions of phloem mobility of SA and various analogs and the actual results, as well as the effect of pCMBS on uptake suggest that SA transport involves a pHdependent carrier system in addition to the ion trap mechanism, at least in the cotyledons of Ricinus communis. Although SA levels increase in both the phloem and systemic leaves after mature leaf infection, this salicylate is clearly not the primary systemic signal which contributes to SAR. Several data strongly suggest J.-L. Bonnemain (&) Laboratoire Écologie et Biologie des Interactions, Université de Poitiers, Unité Mixte de Recherche CNRS 7267, 40 avenue du Recteur Pineau F-86022 Poitiers cedex, France e-mail: [email protected] J.-F. Chollet  F. Rocher Institut de Chimie des Milieux et des Matériaux de Poitiers, Université de Poitiers, Unité Mixte de Recherche CNRS 7285, 40 avenue du Recteur Pineau F-86022 Poitiers cedex, France e-mail: [email protected] F. Rocher e-mail: [email protected]

S. Hayat et al. (eds.), Salicylic Acid, DOI: 10.1007/978-94-007-6428-6_4, Ó Springer Science+Business Media Dordrecht 2013

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that MeSA as well as azelaic acid and small lipids are earlier signals. As MeSA is predicted to be very poorly phloem mobile, the mechanism of long distance transport of this volatile compound remains to be elucidated.







Keywords Salicylic acid Salicylic acid metabolites Salicylic acid analogs Cell compartmentation Long distance transport Ricinus model Diffusion predictors







1 Introduction Salicylic acid (SA) or 2-hydroxybenzoic acid belongs to the very large group of plant phenolics which play an essential role in plant growth, development and interaction with other organisms (Harborne 1980). It has been known for a long time that SA is the natural inducer of thermogenesis in several a

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