Secondary Metabolites: Killing Pathogens

Abstract

Plants produce many antimicrobial secondary metabolites. Two major classes with a demonstrated or proposed role in resistance to plant pathogens are phytoanticipins, or preformed inhibitors, which are present constitutively in plants, and phytoalexins, which are synthesized only in response to pathogen attack. Available evidence is consistent with both phytoanticipins and phytoalexins being important in defence in some disease interactions.

Keywords: phytoalexin; phytoanticipin; plant disease; inducible defence; elicitor

Figure 1.

Structures of three phytoanticipins. Avenacin A‐1 is a triterpenoid saponin from oat (Avena sativa). It is biologically active in its native state and is detoxified by some fungi by hydrolysis of the terminal glucose residues. DIMBOA glucoside is a cyclic hydroxamic acid (benzoxazinone) found in maize (Zea mays), wheat (Triticum aestivum), and rye (Secale cereale). Upon hydrolysis of the glucoside, the compound undergoes spontaneous ring contraction to form the more toxic benzoxazolinone. Dhurrin is a cyanogic glucoside made by sorghum (Sorghum vulgare). Upon hydrolysis of the glucoside, the resulting hydroxynitrile undergoes spontaneous or enzymatic conversion to produce hydrogen cyanide. Some fungi can detoxify cyanide by conversion to formamide.

Figure 2.

Structures of six characteristic phytoalexins. Pisatin is an isoflavonoid of the pterocarpan class produced by pea (Pisum sativum). Rishitin is a bicyclic sesquiterpene made by potato (Solanum tuberosum), and gossypol is a dimeric sesquiterpene phytoalexin made by cotton (Gossypium hirsutum). Wyerone acid is an acetylene produced by Vicia faba. Resveratrol is a stilbene found in several plants including peanut (Arachis hypogaea) and grapevine (Vitis vinifera). Camalexin is a tryptophan derivative found in Arabidopsis thaliana and other species in the Brassicaceae.

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References

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Further Reading

Bailey JA and Mansfield JW (eds) (1982) Phytoalexins. New York: Wiley & Sons.

Kuc J (1995) Phytoalexins, stress metabolism, and disease resistance in plants. Annual Review of Phytopathology 33: 275–297.

Osbourn AE (1996) Preformed antimicrobial compounds and plant defense against fungal attack. Plant Cell 8: 1821–1831.

Smith CJ (1996) Accumulation of phytoalexins: defense mechanism and stimulus response system. New Phytologist 132: 1–45.

VanEtten HD, Matthews DE and Matthews PS (1989) Phytoalexin detoxification: importance for pathogenicity and practical implications. Annual Review of Phytopathology 27: 143–164.

VanEtten HD, Sandrock RW, Wasmann CC et al. (1995) Detoxification of phytoanticipins and phytoalexins by phytopathogenic fungi. Canadian Journal of Botany 73 (supplement): S518–S525.

Zhu Q, DrogeLaser W, Dixon RA and Lamb C (1996) Transcriptional activation of plant defense genes. Current Opinions in Genetics and Development 6: 624–630.

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How to Cite close
Walton, Jonathan D(Apr 2001) Secondary Metabolites: Killing Pathogens. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0000917]