Sinapate esters provide greater UV‐B attenuation than flavonoids in Arabidopsis thaliana (Brassicaceae)

Abstract

Mutants affected in flavonoid (tt4) or sinapate ester (fah1) biosynthesis were used to assess the relative importance of these phenolic UV photoprotectants in Arabidopsis. Flavonoid and sinapate ester absorption was more specific for UV‐B than major nonphenolic chromophores in crude extracts. A new method of evaluating phenolic UV‐B attenuation was developed using fluorescence analysis. When excited by UV‐B, sinapate ester containing leaves and cotyledons had enhanced sinapate ester fluorescence and reduced chlorophyll fluorescence relative to those without sinapate esters. Although fluorescence analysis gave no evidence of UV‐B attenuation by flavonoids, enhanced chlorophyll and protein loss were observed upon UV‐B exposure in flavonoid‐deficient leaves, suggesting they have another mechanism of UV‐B protection. The hydroxycinnamates have been largely ignored as UV‐B attenuating pigments, and the results indicate that greater attention should be paid to their role in attenuating UV‐B.

The effect of u.v.‐B radiation on u.v.‐absorbing secondary metabolites in birch seedlings grown under simulated forest soil conditions

“…Stapleton, 1992;Li et aL, 1993;Middleton & Teramura, 1993;Lois, 1994;Reuber et , 1996). Of the u.v.-B-absorbing compounds other than flavonoids, some phenolic acids (sinapyl esters) and carotenoids have recently been acknowledged to play a role in u.v.-protection (Li et aL, 1993;Middleton & Teramura, 1993;van de Staaij et aL, 1995;Sheahan, 1996). In this study, the amount of chlorogenic acid signiflcantly increased, but the amount of DPPG decreased, in the u.v.-B irradiated seedlings (Table 1).…”

“…Recently, it has been shown that in some plant species, u.v.-B radiation leads to an increase in the * To whom correspondence should be addressed. E-mail: lavola@joyl.joensuu.fi amounts of fiavonoids and phenolic acids (Li et al, 1993;Middleton & Teramura, 1993;Lois, 1994;van de Staaij et al, 1995;Reuber, Bornman & Weissenbock, 1996;Sheahan, 1996;Lavola, 1997). However, changes in individual phenolic components have not yet been widely reported.…”

Flavonoid Profiling and Biosynthetic Gene Expression in Flesh and Peel of Two Tomato Genotypes Grown under UV-B-Depleted Conditions during Ripening

“…Finally, flavonoid-deficient mutants from Arabidopsis thaliana displayed more sensitivity to excessive UV-B irradiation (16), whereas other mutants characterized by high flavonoid content were shown to be less sensitive than wild type (17). Flavonoids are not the only components involved in the plant response to UV-B radiation; other phenolics, such as hydroxycinnamic acids, are also thought to contribute to the plant natural shielding (18).…”

Effects of supplementary ultraviolet-B irradiance on maize yield and qualities: a field experiment

“…The mechanism of UV-B protection includes the accumulation of UV-absorbing compounds in leaf tissue in response to UV-B radiation. The importance of the accumulation of flavonoids in the epidermis in terms of providing UV-B radiation protection has been considered (15,16). There have been many studies to examine UV-B effects on terrestrial plants using growth chambers or greenhouses (17,18).…”