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

Authors: Tisserat, Brent; Vaughn, Steven

Submitted to: In Vitro Cellular and Developmental Biology - Plants
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/19/2006
Publication Date: 1/1/2008
Citation: Tisserat, B., Vaughn, S.F. 2008. Growth, morphogenesis and essential oil production in Mentha spicata L. plantlets in vitro. In Vitro Cellular and Developmental Biology - Plants. 44:40-50.

Interpretive Summary: Spearmint and other Lamiaceae species provide several commercial essential oils. Plant tissue culture technologies offers a means to produce economically important secondary metabolites within controlled laboratory environments. The same essential oil composition found in field grown plants occurs in tissue culture plants. In this study, the influence of the physical cultural supports (vessel size, media replenishment, culture support types) on spearmint plantlets was documented. Enhanced secondary metabolism in vitro coupled with high biomass production was obtained by altering the physical support environment. These techniques can be readily employed to enhance essential oil production in plantlets grown in vitro.

Technical Abstract: The influence of various physical environments were studied on the growth (fresh weight), morphogenesis (leaf, root and shoot numbers) and secondary metabolism [i.e., production of the monoterpene (-)-carvone] of Mentha spicata L. (spearmint) shoots cultured on Murashige and Skoog medium. Carvone analyses of different portions of sterile plantlets were conducted. Shoot tip regions produced the highest carvone concentrations and declined as the distance from the tip increased. Carvone is only produced from the foliar regions of cultured plants and was absent in callus and roots. The type of physical support (e.g., agar, glass, liquid, platform, or sponge) employed within Magenta vessels greatly influenced culture growth and morphogenesis responses. For example, mint shoots grown on the liquid medium produced 3-x fold greater fresh weights than shoots grown on the agar medium. However, carvone concentrations in shoots grown on agar were higher than in shoots grown on liquid medium. Replacing culture media more frequently within Magenta vessels during an 8 week culture period significantly increased growth and morphogenesis without affecting carvone concentrations. The influence of culture vessel capacity on spearmint shoots was tested by culturing shoots on a variety of culture vessels including: culture tubes, Magenta vessels and 1.89 l jars. Positive correlations occurred between culture vessel capacities and culture growth, morphogenesis and carvone concentrations. A comparative study was conducted testing growth, morphogenesis and secondary metabolism occurring with 3 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 one-l medium reservoir. The APCS allowed for the production of greater biomass (e.g., ~12 to 15-x fold increase in fresh weight), and morphogenesis to occur compared to that obtained within culture tubes. However, shoots grown in the APCS produced less carvone compared to shoots grown in agar medium. Carvone concentrations decreased in spearmint shoots grown in the APCS as the distance from the shoot terminus increased. Increasing the number of media immersions (4, 8, 12, or 16 immersions day-1) employing the APCS increased growth and morphogenesis responses. Twelve immersions day-1 of media was optimum for growth and morphogenesis compared to 4, 8 or 16 immersions day-1. Generally, higher culture growth rates resulted in lower carvone concentrations per treatment; however, overall total carvone concentrations per vessel increased due to the greater biomass production occurring per vessel.