The colorless flavonoids of Arabidopsis thaliana (Brassicaceae). II. Flavonoid 3‘ hydroxylation and lipid peroxidation

Abstract

The 3' hydroxylation of kaempferol forms quercetin with an orthodihydroxy structure having two neighboring hydroxyl groups that could theoretically chelate with metal ions and mediate oxidative phenomena. Colorless flavonoids were purified by high pressure liquid chromatography (HPLC) and screened by diode array analysis. The accumulation of quercetin derivatives in Arabidopsis was coordinately regulated with flavonoid biosynthesis in a chalcone isomerase mutant having reduced flux through the biosynthetic pathway, but not within differing wild-type tissues, where seedling, floral, and leaf tissue have a reduced ratio of quercetin to kaempferol derivatives, respectively. The accumulation of lipid peroxidation products in kaempferol proficient mutant seedlings was indistinguishable from that in quercetin proficient wild-type seedlings, leaving no evidence for the role of quercetin antioxidants. However, laser scanning confocal microscopy revealed quercetin derivatives lining the tonoplast of diphenylboric acid 2-aminoethyl ester-stained Arabidopsis seedling tissue and floral papillae, and Norfluorazon induced oxidative stress decreased the most lipophilic of HPLC purified quercetin derivatives. Its potential involvement with lipophyllic oxidative phenomena may warrant further study.

Cytochrome P450CYP78A9Is Involved in Arabidopsis Reproductive Development

“…10A). It has been reported that Arabidopsis leaves have a reduced flux through the flavonoid biosynthetic pathway and accumulate a higher ratio of kaempferol to quercetin derivatives than flowers and seedlings (Sheahan and Cheong, 1998). In line with this, in our study, hardly any quercetin intensities in leaves were detected, and no difference by PCA analysis was found.…”

“…First, kaempferol levels of cyp78a9 and cyp78a8 cyp78a9 mutants were not in accordance with the data reported for the tt7 mutant, deficient in F39H activity, which overaccumulates kaempferol and does not produce quercetin (Shirley et al, 1995;Peer et al, 2001). In this sense, the cyp78a8 cyp78a9 kaempferol profile resembles more the tt5 mutant, which shows a drastically reduced flux through the biosynthetic pathway in relation to the wild type (Sheahan and Cheong, 1998); however, it does not have the same change in testa color: cyp78a8 cyp78a9 has pale brown testa and tt5 has yellowish testa. The profiles reported for tt3 and tt6 mutants did not resemble the situation of our mutant, as tt3 has been reported to accumulate excess quercetin and kaempferol ) and tt6 has reduced kaempferol content and has no quercetin (Shirley et al, 1995).…”

Chloroplast‐located flavonoids can scavenge singlet oxygen

“…6(d). Vacuolar fluorescence attributed to flavonoids was not detected in our experiment, although we do not know to what extent NR is able to enter the vacuole in mesophyll cells (Sheahan & Cheong, 1998). Our data therefore confirm previous reports of a chloroplastic location of flavonoids (Saunders & McClure, 1976; Charriere‐Ladreix & Tissut, 1981; Semerdjieva et al ., 2003; Zaprometov & Nikolaeva, 2003), and lead us to conclude that flavonoids appeared to be optimally located to scavenge the short‐diffusing 1 O 2 generated by the photosynthetic apparatus in P. latifolia leaves under photoinhibition.…”

The colorless flavonoids of Arabidopsis Thaliana (Brassicaceae). I. A model system to study the orthodihydroxy structure

“…Both situations are uncommon, except for relatives of Arabidopsis (Herrmann, 1976). In Arabidopsis leaves, the sinapate esters have greater UV-B attenuation (Sheahan, 1996) and antioxidant activity (Landry, Chapple, and Last, 1995) than flavonoids. Arabidopsis seedlings had greater concentrations of flavonoids and a higher ratio of quercetin to kaempferol derivatives than leaf tissue, but yielded only indirect evidence of orthodihydroxy flavonoid involvement in oxidative phenomena (Sheahan and Cheong, 1997).…”