Altitudinal variation of UV-absorbing compounds in Plantago asiatica

UV-absorbing compounds such as flavonoids and phenolic acids are important for plants to protect their vegetative organs from harmful UV radiation at higher altitude. Two chemotypes, i.e., acteoside mainly-containing (AM) type and plantamajoside mainly-containing (PM) type were found by qualitative HPLC analysis of the phenolics in the leaves of Plantago asiatica in Mt. Norikura, Japan. Though AM type was not detected in low altitude populations, it occurred in high altitude populations. Acteoside has been reported to be more effective antioxidant than plantamajoside. On the other hand, higher accumulations of UV-absorbing substances were seen in higher altitude populations by quantitative analyses. Besides, B-ring ortho-dihydroxylated flavonoids notably increased than mono-hydroxylated flavonoids with increasing altitude. These results demonstrate that P. asiatica has chemically acclimated to high altitudes, in which severe environmental conditions such as higher UV radiation exist.