Do magnetic field applications affect in vitro regeneration, growth, phenolic profiles, antioxidant potential and defense enzyme activities (SOD, CAT and PAL) in lemon balm (Melissa officinalis L.)?

Abstract

Abstract Melissa officinalis L. (lemon balm) is a valuable medicinal plant used in the treatment of nervousness, cardiac failure, hypersensitivities, depression, insomnia, indigestion and colic. Objective of the first part of the study was to determine the effect of 3 different magnetic fields (MF-50\u202fmT, 100\u202fmT and 150\u202fmT) with 5 different exposure times (5\u202fmin, 15\u202fmin, 30\u202fmin, 1\u202fh and 3\u202fh) on in vitro regeneration of explants containing preexisting meristem (axillary, shoot tip and hypocotyl buds). Regenerated shoots were also compared in terms of shoot length, root length, fresh-dry weight and % water content. In the second stage, regenerated shoots obtained from 3 different MF treatments for 1\u202fh and no MF-treated shoots (control) were compared according to their phenolic profile, total phenol-flavonoid content, free radical scavenging activity, superoxide dismutase (SOD), catalase (CAT) and phenylalanine ammonium lyase (PAL) activities. The best regeneration was obtained with axillary buds exposed to 100\u202fmT for 1\u202fh (15.8\u202fshoots at 100 % shoot frequency). Furthermore, 50\u202fmT and 100\u202fmT MF treatments improved the growth parameter and water contents of regenerated shoots. Comparison of 4 different sources (3\u202fMF exposure and no exposure-control) found out that 50\u202fmT MF treatment was the most effective for the enhancement of rosmarinic acid quantity, total phenol-flavonoid content, non-enzymatic antioxidant activity (IC50), stress related enzymatic antioxidant activity (SOD and CAT) and phenol production related PAL enzyme activity. Although 100\u202fmT MF for 1\u202fh treatment was found to be the most potent in regard to number of shoot formation, the most productive shoot length and fresh-dry weight was obtained with 50\u202fmT MF exposure for 1\u202fh. Considering the all results about growth parameters, medicinal quality (rosmarinic acid amount, total phenol-flavonoid content and antioxidant activity) and endurance capacity against stress (SOD, CAT and PAL activities), it can be concluded that exposure to 50\u202fmT MF was the most effective treatment for in vitro culture of M. officinalis.