Complex C-Glycosyl Flavonoid Phytoalexins from Cucumis sativus

Abstract

Extraction of cucumber leaf tissue expressing induced resistance against powdery mildew fungi revealed the presence of two new major C-glycosyl flavonoid products: vitexin-6-(4-hydroxy-1-ethylbenzene) (cucumerin A, 1) and isovitexin-8-(4-hydroxy-1-ethylbenzene) (cucumerin B, 2). In addition, the known C-glycosyl flavonoids apigenin-8-C-beta-D-glucopyranoside (vitexin, 3), apigenin-6-C-beta-D-glucopyranoside (isovitexin, 4), luteolin-8-C-beta-D-glucopyranoside (orientin, 5), and luteolin-6-C-beta-D-glucopyranoside (isoorientin, 6), as well as 4-hydroxycinnamic acid (p-coumaric acid, 7) and its methyl ester (p-came, 8), were found in higher quantities within resistant plants. The structures of 1-8 were elucidated using spectroscopic methods and unambiguously confirmed for 3-8 using co-chromatography experiments with authentic standards. On the basis of the results of this study and the reported biological activities of C-glycosyl flavonoids, these compounds would play a vital role in the defense strategy of this species by acting as phytoalexins.

Identification of a Bifunctional Maize C- and O-Glucosyltransferase

“…In particular, cereals like wheat, rice, and maize mainly accumulate C-glycosyl flavones that are involved in protection against UV-B radiation and defense against pathogens (12)(13)(14). For example, maysin, the C-glycosyl flavone predominant in silk tissues of some maize varieties, is a natural insecticide against the corn earworm Helicoverpa zea (15,16), whereas C-glycosyl flavonoids identified in cucumber leaves act as phytoalexins in defense against powdery mildew fungi (17,18). From another perspective, there is an increasing interest for C-glycosyl flavones because of their benefits for human health and their possible applications in the prevention of diverse diseases (19,20).…”

An Overview of Plant Photosynthesis Modulation by Pathogen Attacks

“…Within each of the major groups of secondary metabolites such as alkaloids, phenylpropanoids and terpenoids, several thousand individual compounds accumulating in plants have been characterised and their role in plant-pathogen interactions studied (Ishihara et al, 2011). For example, induction of phenolic compounds, flavonoid phytoalexins, (Daayf et al, 1997, Fawe et al, 1998, Fofana et al, 2002, McNally et al, 2003b, McNally et al, 2003 was reported in cucumber plants following pathogen attacks and elicitor treatments. Synthesis of phytoalexins involves the rapid transcriptional activation of genes encoding a number of key biosynthetic enzymes that include anthranilate synthase (AS) (IshiharaHashimotoTanaka et al, 2008) phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) which is the early committed key enzyme of the flavonoid/isoflavonoid pathway, chalcone isomerase (CHI) and isoflavone reductase (IFR) (Dixon et al, 1995, Baldridge et al, 1998, Fofana et al, 2002, Fofana et al, 2005.…”

“…Synthesis of phytoalexins involves the rapid transcriptional activation of genes encoding a number of key biosynthetic enzymes that include anthranilate synthase (AS) (IshiharaHashimotoTanaka et al, 2008) phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) which is the early committed key enzyme of the flavonoid/isoflavonoid pathway, chalcone isomerase (CHI) and isoflavone reductase (IFR) (Dixon et al, 1995, Baldridge et al, 1998, Fofana et al, 2002, Fofana et al, 2005. The chemical nature of some of these compounds is now well elucidated (Ibanez et al, 2010, Ishihara et al, 2011, McNally et al, 2003. McNally et al (McNally et al, 2003b, McNally et al, 2003 reported the synthesis of complex C-glycosyl flavonoid phytoalexins, referred to as vitexin-6-(4-hydroxy-1-ethylbenzene) (cucumerin A) and isovitexin-8-(4-hydroxy-1-ethylbenzene) (cucumerin B), as a site-specific response to fungal penetration in cucumber.…”

“…The chemical nature of some of these compounds is now well elucidated (Ibanez et al, 2010, Ishihara et al, 2011, McNally et al, 2003. McNally et al (McNally et al, 2003b, McNally et al, 2003 reported the synthesis of complex C-glycosyl flavonoid phytoalexins, referred to as vitexin-6-(4-hydroxy-1-ethylbenzene) (cucumerin A) and isovitexin-8-(4-hydroxy-1-ethylbenzene) (cucumerin B), as a site-specific response to fungal penetration in cucumber. In a recent study, Ishihara et al (IshiharaHashimotoTanaka et al, 2008) reported on an induced accumulation of Trp-derived secondary metabolites, including tryptamine, serotonin, and hydroxycinnamic acid amides of serotonin in rice leaves by infection with Bipolaris oryzae.…”

Production of <i>C</i>-glucosides of flavonoids and related compounds by <i>Escherichia coli</i> expressing buckwheat <i>C</i>-glucosyltransferase

“…Many kinds of plant C-glycosides have been reported (Franz and Grün 1983), and the most common are the flavonoid C-glycosides that have been found in mosses, liverworts, ferns, gymnosperms, monocots, and dicots (Jay 1994;Talhi and Silva 2012). These C-glycosides are known to show various biological activities in planta, such as antioxidant, antifungal, insecticide, and allelochemical activities (Byrne et al 1996;Hooper et al 2010;Jay 1994;McNally et al 2003). In animals, flavonoid C-glycosides have shown antioxidant, antiinflammatory, antihyperglycemic, anti-obesity, and anti-ulcer activities (reviewed by Talhi and Silva 2012).…”