Metabolomic elucidation of recovery of Melissa officinalis from UV-B irradiation stress

UV irradiation is a major stress and leads to the accumulation of secondary metabolites in plants as a protective mechanism. The altered metabolism caused by the stress will eventually return to basal conditions, however, the recovery mechanism after UV irradiation stress remains unknown. To understand how plant metabolism recovers following UV irradiation stress, global metabolite profiling of Melissa officinalis (lemon balm) was performed using gas chromatography/mass spectrometry (GC/MS). Principal component and hierarchical clustering analyses showed the significant discrimination of metabolite profiles between the control (non-irradiated), UV-irradiated M. officinalis, and M. officinalis allowed to recover from the UV stress. The glycolysis and phenylpropanoid pathway rapidly reverted to their original states. In contrast, the TCA cycle and amino acid biosynthesis returned slowly to their original states. This study determined that the metabolism and metabolite levels recover their original conditions after the removal of UV irradiation, and that the recovery time of each metabolic pathway differs.