Alteration of foliar flavonoid composition induced by enhanced UV-B radiation in Pinus ponderosa, Quercus rubra, Pseudotsuga menziesii and Populus trichocarpa.
Warren1, J.M., J.H. Bassman1, D.S. Mattinson2, J.K. Fellman2, G.E. Edwards3, and R. Robberecht4. 2000.

North American Forest Biology Workshop in Merida, Mexico. July 16-20, 2000.
HPLC analyses of foliage from several common north temperate tree species illustrate the species-specific effects of UV-B radiation on both quantity and composition of foliar flavonoids.  Pinus ponderosa, Quercus rubra and Pseudotsuga menziesii were field-grown under ambient (1X) and elevated (2X) biologically effective UV-B radiation (UV-BBE) for Pullman, WA, USA.  A computer-controlled modulated lamp system was used to supply the supplemental UV-B radiation.  Additionally, Populus tricocarpa was grown in a glasshouse under 0X, 1X and 2X UV-BBE treatments.  Foliage was harvested seasonally over a three-year period, extracted, purified and applied to a μBondapak/C18 column HPLC system sampling at 254 nm.  Twelve standards were applied for comparison and several flavonoids were identified; unknown species are being elucidated via LC-MS.  Higher levels of foliar flavonoids were induced by UV-B radiation in all species.  The two gymnosperms were less affected by the UV-B treatments than the two angiosperms.  Q. rubra foliage flavonoid concentrations were more than twice that of any other species, followed by P.  tricocarpa, P. menziesii and P. ponderosa.  Two-year-old conifer foliage had higher levels of flavonoids than one-year-old tissue.  In addition, the composition of the flavonoids shifted as foliage aged.  Of the 27 flavonoid peaks found in year-old pine foliage, 18 were higher and 3 were lower in the 2X treatment as compared to the 1X treatment.  After two years, only 11 of the flavonoid peaks remained elevated in the 2X treatment, while 7 flavonoids had higher levels in the 1X treatment.  Young tissue of P. tricocarpa had higher concentrations of flavonoids than more mature tissue, which also demonstrated reduced treatment effects.

1Department of Natural Resource Sciences, Washington State University, Pullman, WA 99164-6410 USA

2Department of Horticulture and Landscape Architecture, Washington State University, Pullman, WA 99164-6414 USA

3Department of Botany, Washington State University, Pullman, WA 99164-4238 USA

4Department of Rangeland Ecology, University of Idaho, Moscow, ID 83844-1135 USA