The Metabolism of Sunflower Phytoalexins Ayapin and Scopoletin

Abstract

The coumarin phytoalexins ayapin and scopoletin accumulate in longitudinal stem sections of sunflower (Helianthus annuus L., Compositae) following inoculation with fungi both pathogenic (Alternaria helianthi) and nonpathogenic (Helminthosporium carbonum) to this plant. Both compounds were induced more rapidly, and they attained higher levels in tissue inoculated with the heterologous pathogen H. carbonum as compared with the sunflower pathogen A. helianthi. Similarly, scopoletin and ayapin accumulated to comparatively low concentrations following inoculation with a second sunflower pathogen, Phoma macdonaldii. Scopoletin was biosynthesized de novo following inoculation, although levels of its glucoside scopolin exceeded those of the aglucone in both infected and control tissues. Both scopoletin and scopolin were routinely detected in trace amounts in uninoculated tissue. In contrast, ayapin was not detected as a component of uninfected plants. When [I4Cjscopoletin was supplied to induced sunflower stem sections about 36% of the recovered radioactivity was in the form of ayapin. In vitro studies demonstrated that A. helianthi possessed the ability to rapidly degrade both scopoletin and ayapin, whereas H. carbonum was much less efficient in these traits. The differential degradation of these compounds by phytopathogenic fungi which do not attack sunflower is also discussed.

Effect of defoliation stress on 2-hydroxy cinnamic acid content at different growth stages in Melilotus albus

“…insect or disease damage, inadequate nodulation or nutrient deficiency) tends to decrease the concentration of HCA. Contrary responses have also been reported with other plants; for example, the concentration of 2 coumarin analogues in sunflower increased following insect damage or fungal infection (Olsen and Roseland 1991;Tal and Robeson 1986). The finding of the present study that defoliation triggers an increase in HCA concentration is consistent with the potential role of coumarin and its analogues in the chemical defence against microorganisms, insects or neighbouring plants (Murray et al 1982;Wang et al 2005).…”

Macroevolution of leaf defenses and secondary metabolites across the genus Helianthus

“…The subset of 22 secondary compounds present in at least 20 species of Helianthus is dominated by phenylpropanoids, especially hydroxycinnamoyl‐quinic acid conjugates (Table S1). The list also includes three putative coumarins (coumarin, scopolin, and scopoletin) as well as one putative terpenoid (ciliarin), all of which have been previously reported in sunflowers (Table S1; Tal & Robeson, ; Spring & Schilling, ; Olson & Roseland, ). The overall abundance of these 22 compounds, as described by HeliaMet Subset PC1 (Table S1, Fig.…”

Fungitoxic effect of scopolin and related coumarins on Sclerotinia sclerotiorum. A way to overcome sunflower head rot

“…Coumarins are derived from the "core" phenolic phenylpropanoid biosynthetic pathway (reviewed by Dixon et al, 2002) metabolic flux, which is regulated by the initial conversion of phenylalanine to trans-cinnamic acid by the enzyme phenylalanine ammonia lyase (PAL; Bate et al, 1994). The coumarins scopoletin, its glucosylated form scopolin and ayapin have attracted attention because of evidence that their formation is induced in response to abiotic stress (Cabello-Hurtado et al, 1998;Gutierrez et al, 1995;Jorrin & Prats, 1999;Prats et al, 2000;Serghini et al, 1996), and to attack by both the parasitic plant Orobanche (Serghini, 2000) and pathogenic fungi (Ding et al, 2000;Prats et al, 2002;Tal & Robeson, 1986a, 1986b. Furthermore, ayapin and scopoletin have been shown to have marked antifungal activity in vitro (Tal & Robeson, 1986a,b;Urdangarin et al, 1999).…”