Molecular and phytochemical investigation of medicinal Rhododendron spp. in the Qinghai-Xizang Plateau: the botanical sources of the traditional Tibetan medicine "Tale"

The Qinghai-Xizang Plateau in China is a hotspot for Rhododendron species, with approximately 400 species distributed across the region. Various Rhododendron species in this area have been used medicinally in traditional Tibetan medicine for a long time and are collectively referred to as "Tale." Furthermore, "Tale" is classified as "Talegabao" or "Talenabao," depending on the species. These two types of medicine have similar but distinct properties, and "Talenabao" is usually used as an alternative to "Talegabao." However, differences in their phytochemical compositions and methods for discriminating between them have not been examined. To solve these problems limited the use of "Tale" medicines, 46 plant specimens belonging to nine Rhododendron species were collected from the Qinghai-Xizang Plateau. Molecular methods based on the internal transcribed spacer 2 (ITS2) region of nuclear DNA and psbA-trnH regions of chloroplast DNA were applied to these samples. In addition, 10 flavonoid compounds were quantitatively determined by HPLC. The results indicated psbA-trnH region successfully distinguished the species used as "Talegabao" or "Talenabao," whereas ITS2 failed to distinguish them because of its high degree of conservation. All 10 compounds were detected in all samples. However, the species used as "Talegabao" had more than twice the total content of the 10 flavonoid compounds observed in the species used as "Talenabao." Moreover, differences in the contents of certain compounds among species were detected, indicating potential chemical markers for the quality evaluation of "Tale" medicines. "Talegabao" is the first choice among "Tale" medicines. "Talenabao" can be used as an alternative to "Talegabao"; however, the appropriate dose requires further discussion in practical use. The psbA-trnH region is recommended as a DNA barcode for distinguishing between these two types of medicines.