The aim of this study was to elaborate an efficient in vitro multiplication protocol for Mentha piperita L. (peppermint) and to perform a comparative evaluation of some biochemical compounds in plants regenerated by micropropagation and conventional method. The use of a plain Murashige and Skoog (MS) basal medium favored the induction of regenerative processes, the percentage of explants that started to grow four weeks after inoculation being 92%. The highest multiplication rate (7.12 shoots/explant) and the highest average shoot length (8.11 cm) were obtained on the MS medium supplemented with 1 mg/L benzylaminopurine, when nodal fragments were used as explants. The rooting phase was not necessary, the shoots developing roots on the multiplication medium. The acclimatization rate of in vitro regenerated plants to ex vitro conditions was 96%. Although biochemical investigations revealed some differences between in vitro regenerated plants and those obtained by conventional methods, the results obtained show that micropropagation can be used successfully to obtain high-quality peppermint biological material, a potential source of bioactive compounds with therapeutic effect.

Salvia officinalis L. (sage) and Melissa officinalis L. (lemon balm) are two valuable medicinal plants from Lamiaceae family. Considering the therapeutic potential of sage and lemon balm extracts, there is currently great interest to increase the production of biological material and the synthesis of bioactive compounds by different methods. Both micropropagation and gamma irradiation represent efficient methods of stimulating the synthesis of bioactive compounds in plants. In order to produce biological material, it is important to establish the doses of gamma radiation that do not have a phytotoxic effect on plants. The aim of the present study was to evaluate the effect of different doses of gamma irradiation (100, 300, and 500 Gy) on sage and lemon balm by quantifying of some biochemical compounds (assimilatory pigments, soluble carbohydrates, and total polyphenols) in in vitro plants. The results obtained revealed that high doses of gamma radiation have phytotoxic effect on in vitro raised plants. However, micropropagation is an efficient method to produce high quality biological material, source for obtaining extracts with therapeutic potential.