|HUGHES, NICOLE - High Point University|
|CAVENDER-BARES, JEANNINE - University Of Minnesota|
|SMITH, WILLIAM - Wake Forest University|
Submitted to: Journal of Experimental Botany
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/19/2011
Publication Date: 3/1/2012
Citation: Hughes, N.M., Burkey, K.O., Cavender-Bares, J., Smith, W.K. 2012. Xanthophyll cycle pigment and antioxidant profiles of winter-red (anthocyanic) and winter-green (acyanic) angiosperm evergreen species. Journal of Experimental Botany. 63:1895-1905.
Interpretive Summary: Less than ten percent of light absorbed by plants is used to fix carbon dioxide through photosynthesis. The remainder of the light energy must be dissipated within the leaf by mechanisms that prevent formation of reactive oxygen molecules capable of damaging tissue. This challenge is even greater for evergreen plants that retain leaves during the winter and continue to absorb light when both photosynthesis and general physiology are suppressed by cold temperature. In this study, evergreen species that turn red in the winter were compared with evergreen species that remain green to determine the role of red pigments called anthocyanins in dissipation of excess light energy. Biophysical and biochemical approaches were used to show that anthocyanins in winter-red species serve a photoprotective function not found in winter-green species. The results enhance our knowledge of the mechanisms in plants that mediate environmental stress.
Technical Abstract: Leaves of many angiosperm evergreen species turn red during winter, corresponding with synthesis of anthocyanin pigments. The function of winter color change, and why it occurs in some species and not others, is not yet understood. We hypothesized that anthocyanins play a compensatory photoprotective role in species with limited capacity for energy dissipation. We compared seasonal xanthophyll pigment content, chlorophyll fluorescence, leaf nitrogen, and low molecular weight antioxidants (LMWA) of five winter-red and five winter-green angiosperm evergreen species. Our results showed no difference in seasonal xanthophyll pigment content (V+A+Z per g leaf dry mass) or LMWA between winter-red and winter-green species, indicating red-leafed species are not deficient in their capacity for these types of non-photochemical energy dissipation. Winter-red and winter-green species also did not differ in percent leaf nitrogen, consistent with our previous studies showing no difference in seasonal photosynthesis under saturating irradiance. Consistent with a photoprotective function of anthocyanin, winter-red species had significantly lower xanthophyll content on per unit chlorophyll, and less sustained photoinhibition than winter-green species (higher pre-dawn Fv/Fm and a lower proportion of de-epoxidized xanthophylls retained overnight). Red-leafed species also maintained a higher maximum quantum yield efficiency of PSII at mid-day (Fv’/Fm’) during winter, and showed characteristics of shade acclimation (positive correlation between anthocyanin and chlorophyll content, and negative correlation with chlorophyll a/b). The results suggest that the capacity for energy dissipation (photochemical and non-photochemical) is not limited in red-leafed species, and that anthocyanins more likely function as an alternative photoprotective strategy to increased VAZ/Chl during winter.