Hydroxycinnamic acids in sunflower leaves serve as UV-A screening pigments

Flavonoids and hydroxycinnamic acid derivatives, which are located in the upper epidermis of plants, are well known to screen ultraviolet radiation, thus protecting the underlying tissue from these harmful wavelengths. Both classes of secondary products complement each other over the UV spectral reg...

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Bibliographic Details
Published in:Photochemical & photobiological sciences 2019, Vol.18 (7), p.1649-1659
Main Authors: Stelzner, Jana, Roemhild, Roderich, Garibay-Hernández, Adriana, Harbaum-Piayda, Britta, Mock, Hans-Peter, Bilger, Wolfgang
Format: Article
Language:English
Subjects:
Absorption spectra
Attenuators
Biochemistry
Biomaterials
Chemistry
Deactivation
Derivatives
Epidermis
Flavonoids
High-performance liquid chromatography
Hydroxycinnamic acid
Inactivation
Leaves
Liquid chromatography
Microscopy
Photosystem II
Physical Chemistry
Pigments
Plant protection
Plant Sciences
Quinic acid
Screening
Sunflowers
Transmittance
Ultraviolet radiation
Vacuoles
Wavelengths
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Summary:Flavonoids and hydroxycinnamic acid derivatives, which are located in the upper epidermis of plants, are well known to screen ultraviolet radiation, thus protecting the underlying tissue from these harmful wavelengths. Both classes of secondary products complement each other over the UV spectral region according to their absorption spectra: flavonoids are most efficient as UV-A attenuators while hydroxycinnamates (HCAs) screen well within the UV-B region. Analysis of epidermal transmittance revealed a substantial UV-A screen in Helianthus annuus L. cv. Peredovick. Identifying responsible pigments by HPLC-MS, we found surprisingly low amounts of flavonoids but dominant abundance of the HCA derivatives chlorogenic and di-caffeoyl quinic acid. Both display low UV-A absorbance and thus, should contribute only a little to UV-A protection. However, growth at high light led to a decrease of epidermal transmittance at 366 nm of up to 90%. Underpinning the screening role, HCA autofluorescence microscopy revealed storage to occur predominantly in vacuoles of the upper epidermis. UV-A treatment in the absence of D1-repair resulted in photosystem II inactivation proportional to epidermal UV-A transmittance. Our findings suggest that UV-A protection can be achieved solely with HCAs, apparently through accumulation of high amounts of these compounds. Despite the weak absorption of hydroxycinnamic acids in the UV-A region, we found evidence that these compounds protect against damage induced by UV-A radiation in sunflowers.
ISSN:1474-905X
1474-9092
1474-9092
DOI:10.1039/c8pp00440d