The influence of altering the physical environment on the growth (fresh weight), morphogenesis (leaf, root, and shoot numbers) and secondary metabolism (i.e., volatile monoterpene, and carvone) of Mentha spicata L. (spearmint) shoots cultured on MS medium was studied. The type of physical support (e.g., agar, liquid, platforms, or glass supports) using Magenta vessels altered growth and morphogenesis. Mint shoots grown on liquid produced 4-x fold more fresh weight than on agar. Carvone levels were unaffected physical supports. Increasing the frequency of media replacement significantly increased growth without altering carvone. Vessel size influence was tested by culturing shoots on culture tubes, Magenta vessels and ½-gal. jars. Positive correlations occurred between vessel capacity and culture growth, morphogenesis and carvone levels. A comparative study testing several spearmint cultivars on either culture tubes or an automated plant culture system (APCS, a sterile hydroponics system) was conducted. The APCS produced more biomass (e.g., ≈15-x fold increase in fresh weight), morphogenesis and carvone than employing culture tubes. Carvone was only produced from shoots and was absent in either roots or callus. Carvone levels decreased proportionally in shoots as the distance from the shoot terminus increased. Altering the number of media culture immersions (4, 8, 12, or 16 immersions/day) with the APCS was tested. Twelve immersions of media/day was optimum. Higher culture growth rates resulted in lower carvone levels/culture; however, overall carvone levels/vessel increased due to greater biomass production.
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