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Effects of Ultraviolet‐A Exposure on Ultraviolet‐B–induced Accumulation of Specific Flavonoids in Brassica napus ¶
Author(s) -
Wilson Kenneth E.,
Thompson John E.,
Huner Norman P. A.,
Greenberg Bruce M.
Publication year - 2001
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2001)0730678eouaeo2.0.co2
Subject(s) - brassica , quercetin , flavonoid , botany , photoprotection , antioxidant , ultraviolet b , flavonols , biology , chemistry , epidermis (zoology) , biochemistry , photosynthesis , medicine , anatomy , dermatology
ABSTRACT Many plant species are able to acclimate to changes in ultraviolet‐B radiation (UVB) (290–320 nm) exposure. Due to the wide range of targets of UVB, plants have evolved diverse repair and protection mechanisms. These include increased biosynthesis of UVB screening compounds, elevated antioxidant activity and increased rates of DNA repair. We have shown previously that Brassica napus L. cv Topas plants can acclimate quite effectively to environmentally relevant increases in UVB through the accumulation of specific flavonoids in the leaf epidermis. However, B. napus was found to lose other flavonoids when plants are exposed to ultraviolet‐A radiation (UVA) (320–400 nm) and/or UVB (Wilson et al. [1998] Photochem. Photobiol. 67 , 547–553). In this study we demonstrate that the levels of all the extractable flavonoids in the leaves of B. napus plants are decreased in a dose‐dependent manner in response to UVA exposure. Additionally, the accumulation of the extractable flavonoids was examined following a shift from photosynthetically active radiation (PAR) + UVA to PAR + UVB to assess if preexposure to UVA affected UVB‐induced flavonoid accumulation. UVA preexposures were found to impede UVB‐induced accumulation of some flavonoids. This down regulation was particularly evident for quercetin‐3‐ O ‐sophoroside and quercetin‐3‐ O ‐sophoroside‐7‐ O ‐glucoside, which is interesting because quercetins have been demonstrated to be induced by UVB and correlated with UVB tolerance in some plant species. The photobiological nature of these UVA‐mediated effects on flavonoid accumulation implies complex interactions between UVA and UVB responses.