Response of selected antioxidants and pigments in tissues of Rosa hybrida and Fuchsia hybrida to supplemental UV-A exposure

The effect of supplemental UV-A (320–400 nm) radiation on tissue absorption at 355 nm, levels of various antioxidants (ascorbate, glutathione, carotenoids and flavonoids) and of antioxidant scavenging capacity were investigated with leaves and petals of Rosa hybrida , cv. Honesty and with leaves, petals and sepals of Fuchsia hybrida , cv. Dollarprinzessin. Supplemental UV-A did not result in visible changes in plant morphology of either species. In leaves it induced small increases in levels of chlorophylls a and b , the carotenoids antheraxanthin, lutein and β-carotene, and high increases in the flavonols quercetin and kaempferol. Petals hardly responded, while the coloured sepals of fuchsia showed an increase in quercetin derivatives. HPLC of unhydrolysed flavonoids showed that individual quercetin derivatives in leaves of both species and kaempferol derivatives in rose leaves increased 2-fold. Some kaempferol derivatives in fuchsia leaves were more than 2-fold enhanced or were newly induced by supplemental UV-A. Increases in l-ascorbic acid levels in fuchsia leaves, and decreases in rose leaves as result of supplemental UV-A were observed, but differences appeared statistically not significant, while l-ascorbate levels remained unchanged in the other tissues investigated. Anthocyanins and reduced glutathione levels were unaffected in all tissues. The combined UV-A induced increases in concentrations of these antioxidant species, did not lead to significant increases in antioxidant capacity of tissues, measured as Trolox equivalents in 50%-ethanol extracts. Light absorption at 355 nm of leaf extracts was significantly increased upon UV-A exposure. Our results indicate that the major protection towards UV-A exposure, in particular in the leaves, will originate from absorption of irradiation, and not from scavenging reactive oxygen species.