Characterization of glandular trichomes of Minthostachys verticillata “peperina” from northwest and central Argentina: relation with essential oil content

Abstract

Minthostachys verticillata is an endemic species in Argentina that shows higher contents of essential oils (EO %, v/w) in plants from the central area than in those from the northwest. Although the reason for this difference is still unknown, studies on species from this family indicate that the variation in essential oil yields could be due to genetic or environmental factors or their interaction, which modifies the number and size of the glandular trichomes, structures where the oil is synthesized and stored. The main objective of this study was to analyze the density and size of glandular trichomes on M. verticillata leaves and their relation to the EO in wild plants from northwestern (NA) and central Argentina (CA); and then in a semi controlled environment, we studied the relation between the density and size of these to the leaf size (apical vs basal leaves) and plant origin. For the first experiment, we collected random wild plants in the main natural areas of distribution; and in the second one, we used cloned plants and grew them in a completely randomized design. The analyses of the trichome density and size and the EO% were carried out using a transmission electron microscope and a Clevenger type trap respectively. The wild plants from the central area showed larger glandular trichomes and higher EO concentrations; in addition, under semi-controlled conditions, we also found a greater number of trichomes per mm2 in both apical and basal leaves in the plant from CA than in that from NA. Thus, the trichome size and number were affected in a different way by the environment.