Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Vitamin C degradation in plant cells via enzymatic hydrolysis of 4-O-oxalyl-l-threonate


Increasing the l-ascorbate (vitamin C) content of crops could in principle involve promoting its biosynthesis or inhibiting its degradation. Recent progress has revealed biosynthetic pathways for ascorbate1,2,3, but the degradative pathways remain unclear. The elucidation of such pathways could promote an understanding of the roles of ascorbate in plants4, and especially of the intriguing positive correlation between growth rate and ascorbate oxidase5,6 (or its products7). In some plants (Vitaceae), ascorbate is degraded via l-idonate to l-threarate (l-tartrate), with the latter arising from carbons 1–4 of ascorbate3,8,9,10,11. In most plants, however (including Vitaceae)11, ascorbate degradation can occur via dehydroascorbate, yielding oxalate12 plus l-threonate, with the latter from carbons 3–6 of ascorbate3,10,13. The metabolic steps between ascorbate and oxalate/l-threonate, and their subcellular location, were unknown. Here we show that this pathway operates extracellularly in cultured Rosa cells, proceeds via several novel intermediates including 4-O-oxalyl-l-threonate, and involves at least one new enzyme activity. The pathway can also operate non-enzymatically, potentially accounting for vitamin losses during cooking. Several steps in the pathway may generate peroxide; this may contribute to the role of ascorbate as a pro-oxidant14,15 that is potentially capable of loosening the plant cell wall and/or triggering an oxidative burst.

This is a preview of subscription content, access via your institution

Access options

Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Chemical characterization and metabolism of product F (4-O-oxalyl-l-threonate).
Figure 2: Periodate oxidation of 14C-F.
Figure 3: Inter-conversions involving compounds C, D, E, F and G (proposed chemical identities of D, F and G are shown in Fig. 4e).
Figure 4: Enzymatic and non-enzymatic degradation of vitamin C.


  1. Wheeler, G. L., Jones, M. A. & Smirnoff, N. The biosynthetic pathway of vitamin C in higher plants. Nature 393, 365–369 (1998)

    ADS  CAS  Article  Google Scholar 

  2. Agius, F. et al. Engineering increased vitamin C levels in plants by overexpression of a d-galacturonic acid reductase. Nature Biotechnol. 21, 177–181 (2003)

    CAS  Article  Google Scholar 

  3. Asard, H., May, J. M. & Smirnoff, N. (eds) Vitamin C Function and Biochemistry in Animals and Plants (Bios Scientific Publishers, London, 2004)

  4. Smirnoff, N. The function and metabolism of ascorbic acid in plants. Ann. Bot. 78, 661–669 (1996)

    CAS  Article  Google Scholar 

  5. Lin, L. S. & Varner, J. E. Expression of ascorbic acid oxidase in zucchini squash (Cucurbita pepo L). Plant Physiol. 96, 159–165 (1991)

    CAS  Article  Google Scholar 

  6. Pignocchi, C., Fletcher, J. M., Wilkinson, J. E., Barnes, J. D. & Foyer, C. H. The function of ascorbate oxidase in tobacco. Plant Physiol. 132, 1631–1641 (2003)

    CAS  Article  Google Scholar 

  7. Hidalgo, A., García-Herdugo, G., González-Reyes, J. A., Morré, D. J. & Navas, P. Ascorbate free-radical stimulates onion root growth by increasing cell elongation. Bot. Gaz. 152, 282–288 (1991)

    CAS  Article  Google Scholar 

  8. Williams, M. & Loewus, F. A. Biosynthesis of (+ )-tartaric acid from l-ascorbic-4-C14 acid in grape and geranium. Plant Physiol. 61, 672–674 (1978)

    CAS  Article  Google Scholar 

  9. Saito, K. & Kasai, Z. Synthesis of l-(+ )-tartaric acid from l-ascorbic-acid via 5-keto-d-gluconic acid in grapes. Plant Physiol. 76, 170–174 (1984)

    CAS  Article  Google Scholar 

  10. Saito, K., Ohmoto, J. & Kuriha, N. Incorporation of 18O into oxalic, l-threonic and l-tartaric acids during cleavage of l-ascorbic and 5-keto-d-gluconic acids in plants. Phytochemistry 44, 805–809 (1997)

    CAS  Article  Google Scholar 

  11. deBolt, S., Hardie, J., Tyerman, S. & Ford, C. M. Composition and synthesis of raphide crystals and druse crystals in berries of Vitis vinifera L. cv. Cabernet Sauvignon: ascorbic acid as precursor for both oxalic and tartaric acids as revealed by radiolabelling studies. Aust. J. Grape Wine Res. 10, 134–142 (2004)

    CAS  Article  Google Scholar 

  12. Yang, J. C. & Loewus, F. A. Metabolic conversion of l-ascorbic-acid to oxalic-acid in oxalate-accumulating plants. Plant Physiol. 56, 283–285 (1975)

    CAS  Article  Google Scholar 

  13. Helsper, J. P. & Loewus, F. A. Metabolism of l-threonic acid in Rumex × acutus L. and Pelargonium crispum (L.) l'Hér. Plant Physiol. 69, 1365–1368 (1982)

    CAS  Article  Google Scholar 

  14. Podmore, I. D. et al. Vitamin C exhibits pro-oxidant properties. Nature 392, 559 (1998)

    ADS  CAS  Article  Google Scholar 

  15. Fry, S. C. Oxidative scission of plant cell wall polysaccharides by ascorbate-induced hydroxyl radicals. Biochem. J. 332, 507–515 (1998)

    CAS  Article  Google Scholar 

  16. Takahama, U. Redox state of ascorbic acid in the apoplast of stems of Kalanchoë daigremontiana . Plant Physiol. 89, 791–798 (1993)

    CAS  Article  Google Scholar 

  17. Offord, R. E. Electrophoretic mobilities of peptides on paper and their use in the determination of amide groups. Nature 211, 591–593 (1966)

    ADS  CAS  Article  Google Scholar 

  18. Deutsch, J. C. Oxygen-accepting antioxidants which arise during ascorbate oxidation. Anal. Biochem. 265, 238–245 (1998)

    CAS  Article  Google Scholar 

  19. Dekker, A. O. & Dickinson, R. G. Oxidation of ascorbic acid by oxygen with cupric ion as catalyst. J. Am. Chem. Soc. 62, 2165–2171 (1940)

    CAS  Article  Google Scholar 

  20. Lane, B. G., Dunwell, J. M., Ray, J. A., Schmitt, M. R. & Cuming, A. C. Germin, a protein marker of early plant development, is an oxalate oxidase. J. Biol. Chem. 268, 12239–12242 (1993)

    CAS  PubMed  Google Scholar 

  21. Saito, K. Metabolism of l-threotetruronic acid by Pelargonium crispum . Phytochemistry 31, 1219–1222 (1992)

    CAS  Article  Google Scholar 

  22. Halliwell, B. & Gutteridge, J. M. C. Role of free radicals and catalytic metal ions in human disease: an overview. Methods Enzymol. 186, 1–85 (1990)

    CAS  Article  Google Scholar 

  23. Schopfer, P. Hydroxyl radical-induced cell-wall loosening in vitro and in vivo: implications for the control of elongation growth. Plant J. 28, 679–688 (2001)

    CAS  Article  Google Scholar 

  24. Rodríguez, A. A., Grunberg, K. A. & Taleisnik, E. L. Reactive oxygen species in the elongation zone of maize leaves are necessary for leaf extension. Plant Physiol. 129, 1627–1632 (2002)

    Article  Google Scholar 

  25. Dumville, J. C. & Fry, S. C. Solubilisation of tomato fruit pectins by ascorbate: a possible non-enzymic mechanism of fruit softening. Planta 217, 951–961 (2003)

    CAS  Article  Google Scholar 

  26. Plochl, M., Lyons, T., Ollerenshaw, J. & Barnes, J. Simulating ozone detoxification in the leaf apoplast through the direct reaction with ascorbate. Planta 210, 454–467 (2000)

    CAS  Article  Google Scholar 

  27. Conklin, P. L., Williams, E. H. & Last, R. L. Environmental stress sensitivity of an ascorbic acid-deficient Arabidopsis mutant. Proc. Natl Acad. Sci. USA 93, 9970–9974 (1996)

    ADS  CAS  Article  Google Scholar 

  28. Keates, S. E., Tarlyl, N. M., Loewus, F. A. & Franceschi, V. R. l-Ascorbic acid and l-galactose are sources for oxalic acid and calcium oxalate in Pistia stratiotes . Phytochemistry 53, 433–440 (2000)

    CAS  Article  Google Scholar 

  29. Fry, S. C. & Street, H. E. Gibberellin-sensitive suspension cultures. Plant Physiol. 65, 472–477 (1980)

    CAS  Article  Google Scholar 

  30. Fry, S. C. The Growing Plant Cell Wall: Chemical and Metabolic Analysis Reprint edn< (Blackburn Press, Caldwell, New Jersey, 2000)

    Google Scholar 

Download references


We thank B. Dudley and J. Miller for technical assistance. M.A.G. thanks the BBSRC for a research studentship.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Stephen C. Fry.

Ethics declarations

Competing interests

The authors declare that they have no competing financial interests.

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Green, M., Fry, S. Vitamin C degradation in plant cells via enzymatic hydrolysis of 4-O-oxalyl-l-threonate. Nature 433, 83–87 (2005).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing