Growth, morphogenesis, and essential oil production in Mentha spicata L. plantlets in vitro

Abstract

To date, plantlet culture has not been explored as a means to obtain secondary metabolites in vitro. However, plantlets readily produce desirable secondary metabolites, which may not be produced in cell suspension or callus cultures. To optimize plantlet growth in vitro, the influences of various physical environments on the growth (fresh weight), morphogenesis (leaf, root, and shoot number), and volatile carbon metabolites (i.e. monoterpene, (−)-carvone) of Mentha spicata L. (spearmint) plants were studied. The carvone content in different portions of sterile plantlets was analyzed. Carvone was only produced from the foliar regions of cultured plantlets and was absent in the callus and roots. The influence of physical support (e.g., agar, glass gravel, liquid, platform or sponge), frequency of media replacement, and culture vessel capacity on spearmint plantlets growth and carvone production was tested. A comparative study was conducted testing the growth, morphogenesis, and secondary metabolism occurring with three different spearmint cultivars grown in either culture tubes containing 25 ml agar medium or in an automated plant culture system (APCS; a sterile hydroponics system) employing a 1-l medium reservoir. Increasing the number of media immersions (4, 8, 12 or 16 immersions d−1) of plantlets growing in the APCS increased growth and morphogenesis responses. Generally, higher culture growth rates resulted in lower carvone treatment−1 (mg carvone g-FW−1); however, overall total carvone ((mg carvone g-FW−1) × g culture FW) increased because of the production of greater biomass obtained per vessel.