Metabolic programming of Rhododendron chrysanthum leaves following exposure to UVB irradiation

Excessive UVB reaching the earth is a cause for concern. To decipher the mechanism concerning UVB resistance of plants, we studied the effects of UVB radiation on photosynthesis and metabolic profiling of Rhododendron chrysanthum Pall. by applying 2.3Wm-2 of UVB radiation for 2days. Results showed that maximum quantum yield of PSII (Fv/Fm) and effective quantum yield of PSII (φPSII) decreased by 7.95% and 8.36%, respectively, following UVB exposure. Twenty five known metabolites were identified as most important by two different methods, including univariate and multivariate statistical analyses. Treatment of R. chrysanthum with UVB increased the abundance of flavonoids, organic acids, and amino acids by 62%, 22%, and 5%, respectively. UVB irradiation also induced about 1.18-fold increase in 11 top-ranked metabolites identified: five organic acids (d-2,3-dihydroxypropanoic acid, maleic acid, glyceric acid, fumaric acid and suberic acid), four amino acids (l-norleucine, 3-oxoalanine, l-serine and glycine), and two fatty acids (pelargonic acid and myristoleic acid). In addition, UVB irradiation increased the intermediate products of arginine biosynthesis and the TCA cycle. Taken together, the accumulation of flavonoids, organic acids, amino acids and fatty acids, accompanied by enhancement of TCA cycle and arginine biosynthesis, may protect R. chrysanthum plants against UVB deleterious effects.