Rhododendron Microshoot Culture as a Source of Phenolic Antioxidants for Biomedicine

The search for alternative sources of biologically active compounds of plant origin, including phenolic compounds (PCs), is of great importance in medicine and pharmacology. Morphophysiological characteristics, photosynthetic pigments, PCs content, phenolic profile, as well as antioxidant (AOA) and antiradical activity (ARA), were studied for in vitro rhododendrons' microshoots (R. smirnowii, R. PJM Elite, R. japonicum). The microshoots of R. PJM Elite had the highest photosynthetic pigments content (chlorophylls a and b), exceeding that of R. smirnowii and R. japonicum, it was 33% and 42%, respectively. The total phenolic content increased in the row R. PJM Elite < R. smirnowii < R. japonicum. Twelve to twenty phenolic compounds were identified in ethanol extracts of rhododendron microshoots, using high-performance liquid chromatography. Quercetin, kaempferol, and myricetin dominated in the phenolic complex of R. japonicum and R. smirnowii, whereas in R. PJM Elite, they were taxifolin and (-)-epicatechin. The AOA and ARA evaluation in DPPH-radical system and the model of initiated liposomes oxidation allowed to determine the highest activity in both systems for R. japonicum extracts, which was not typical for the other two species extracts. A high correlation was found between AOA extracts and the flavonoid content in them. The results obtained indicate the prospects of using R. japonicum and R. PJM Elite microshoots as an alternative source of flavonols and flavanols, accordingly.