The Ghirardi botanic garden, beyond the visible

Plants preserved in botanic gardens are primarily experienced for their aesthetic value, often losing their identity to give rise to a whole that welcomes visitors. However, beyond the visual display, each plant dialogues with the other living organisms through the production of a plethora of different secondary metabolites. In this perspective, botanic gardens become not only showcases of plant beauty, but also factories of molecules that drive multiple biotic interactions. Under this novel inquiring approach, botanic gardens may be explored for intrinsic features lying at a higher level than that visually perceived. In this framework, we planned a research project on 30 selected medicinal species preserved at the Ghirardi Botanic Garden (Toscolano Maderno, Bs) on the basis of their productivity in volatile compounds (VOCs), essential oils (EOs), epicuticular depositions and substances stored at tissue level. The project encompasses analyses on the: (i) micromorphology of the secretory structures; (ii) the chemistry of the secondary metabolites; (iii) the evaluation of their ecological roles and (iv) of their biological activity. By way of example, we presented hereafter the results of the investigations performed on some target-species for each of the three-scale analyses. (i) We addressed our attention on Cinnamomum camphora (L.) J.Presl. The structures responsible for oil synthesis and storage were secretory cells distributed in the foliar mesophyll, in the bark and in close association to the xylem medullary rays. (ii) We analysed the composition of the EOs obtained from the leaves of Myrtus communis L., following different preservation procedures: fresh, dried and stored at room temperature, dried and stored at -20°C, dried and stored at -80°C. A high level of chemical consistency emerged across the EOs, due to the occurrence of 11 common compounds that included the main constituents. (iii) We observed the peculiar handling strategies of the local insect visitors on the flowers of two Mexican sage species: Salvia blepharophylla Brandegee (ex Epling) and Salvia greggii A. Gray. (iv) We evaluated the antimalarial activity on Plasmodium falciparum chloroquine (CQ)-sensitive (D10) and CQresistant (W2) strains and the antileishmanial activity on Leishmania infantum and Leishmania tropica of the EO of Eugenia uniflora L. aerial parts. The cytotoxicity of the oils was evaluated on human cells to calculate the selectivity index. E. uniflora showed antimalarial and antileishmanial activity at micromolar concentrations, but exhibited high cytotoxicity. The overall results were discussed in the light of the most recent literature contributions.