Effects of solar UV-A and UV-B radiation on gene expression and phenolic accumulation in Betula pendula leaves

Summary Ultraviolet (UV) radiation is an important environmental factor for plant communities; however, plant re-sponses to solar UV are not fully understood. Here, we report differential effects of solar UV-A and UV-B radiation on the expression of flavonoid pathway genes and phenolic accu-mulation in leaves of Betula pendula Roth (silver birch) seedlings grown outdoors. Plants were exposed for 30 days to six UV treatments created using three types of plastic film. Epidermal flavonoids measured in vivo decreased when UV-B was excluded. In addition, the concentrations of six flavonoids determined by high-performance liquid chro-matography-mass spectrometry declined linearly with UV-B exclusion, and transcripts of PAL andHYHmeasured by quan-titative real-time polymerase chain reaction were expressed at lower levels. UV-A linearly regulated the accumulation of quercetin-3-galactoside and quercetin-3-arabinopyranoside and had a quadratic effect on HYH expression. Furthermore, there were strong positive correlations between PAL expres-sion and accumulation of four flavonols under the UV treat-ments. Our findings in silver birch contribute to a more detailed understanding of plant responses to solar UVradiation at both molecular and metabolite levels