Increased Antioxidant Activity, Despite Reduced Rosmarinic Acid Accumulation in Methanolic Extracts, of Spearmint (Mentha spicata L.) Plantlets Regenerated In Vitro

One hundred spearmint (Mentha spicata) plantlets were regenerated from apical shoot segments of ten field- grown donor plants. Although the accumulation of rosmarinic acid and total phenolics in vitro was almost half than in vivo, regenerants demonstrated a tenfold-higher hydrogen peroxide compared to the donor plants. This finding may have been associated with the increased activity of hydroxyphenylpyruvate reductase, a key enzyme of the phenolic biosyn- thetic pathway and the increased production of yet unidentified phenolic compounds in vitro. This process of in vitro cul- ture associated with a reduction of rosmarinic acid and total phenolics and with an increase of the antioxidant capacity in- dicated the possible promotion of in vitro-specific biosynthetic pathways.