Influence of in vitro growth conditions in the production of defence compounds in Mentha pulegium L.

- Increased MI induces the production of lateral roots and root exudates.
- Increased MI induces the production of essential oils and biomass.
- Increased MI and water stress increases the number of trichomes and leaf hairs.
- Pulegone contain increases both with MI and water stress.

The content in secondary metabolites greatly affects the quality of plants used for food consumption. Specifically, the production of defence secondary metabolites is triggered by a number of biotic and abiotic stress factors. Commonly studied biotic factors include insects and other herbivores that cause wounding and tissue damage due to microorganisms. Among abiotic factors, mechanical stress induced in the roots has yet to be studied in depth. Such studies are of interest because of the influence of this factor on plants grown under in vitro conditions. Herein, we present our results on essential oil production and other defence-related morphological traits in terms of the effect of mechanical stress induced in the roots of Mentha pulegium plants grown under different conditions: greenhouse using soil as support and non-soil in vitro conditions using gelose and glass beads. A positive correlation has been found between secondary metabolites production, i.e. essential oil and growth conditions. The presence and development of morphological characteristics linked to their storage and lixiviation into the environment - trichomes and glandular hairs in the leaves; lateral roots and fibrous roots - has also been positively related to an increase in penetration resistance on the roots by the substrate - mechanical impedance. Pulegone is the major defence compound in pennyroyal essential oil. Pulegone production and other essential oil constituents present in trichomes have been quantified under different growth conditions and the results have been correlated with morphological characteristics and growth conditions.