Effects of PAR and UV-B radiation on herbal yield, bioactive compounds and their antioxidant capacity of some medicinal plants under controlled environmental conditions.

Photosynthetically active radiation (PAR) and Ultraviolet B (UV-B) radiation are among the main environmental factors acting on herbal yield and biosynthesis of bioactive compounds in medicinal plants. The objective of this study was to evaluate the influence of biologically effective UV-B light (280-315 nm) and PAR (400-700 nm) on herbal yield, content and composition, as well as antioxidant capacity of essential oils and polyphenols of lemon catmint (Nepeta cataria L. f. citriodora), lemon balm (Melissa officinalis L.) and sage (Salvia officinalis L.) under controlled greenhouse cultivation. Intensive UV-B radiation (2.5 kJ m(-2)  d(-1) ) influenced positively the herbal yield. The essential oil content and composition of studied herbs were mainly affected by PAR and UV-B radiation. In general, additional low-dose UV-B radiation (1 kJ m(-2) d(-1) ) was most effective for biosynthesis of polyphenols in herbs. Analysis of major polyphenolic compounds provided differences in sensitivity of main polyphenols to PAR and UV-B radiation. Essential oils and polyphenol-rich extracts of radiated herbs showed essential differences in antioxidant capacity by the ABTS system. Information from this study can be useful for herbal biomass and secondary metabolite production with superior quality under controlled environment conditions.