Sage at the botanic garden: GC-MS characterization of the lipophilic epicuticular depositions and tissue content

A deep characterization of the metabolite profile of four target species – Salvia verticillata, S. uliginosa, S. blepharophylla and S. greggii – preserved at the “G.E. Ghirardi” Botanic Garden of the University of Milan (Toscolano Maderno, Brescia), was achieved. In particular, we evaluated and compared the composition of (i) the lipophilic epicuticular exudates with (ii) the lipophilic tissue content of both leaves and flowers. Selective solvent extractions were carried out with acetone (after soaking of the entire leaves and flower), and n-hexane (after grinding of the plant material), respectively, and the dried extracts analyzed by GC-MS after derivatization with HCl-saturated methanol. The composition of all the extracts was dominated by: hydrocarbon compounds (24.0 – 86.0%), with the exception of the leaf n-hexane extract of S. uliginosa (0.7%) and of the acetone and n-hexane extracts of S. greggii obtained both from leaves and flowers (2.6% and 5.2%); fatty acids (e.g., υ3 linolenic acid ranging from n.d. in S. uliginosa up to 29.0% in the n-hexane extract of S. greggii flowers). In addition, it is noteworthy the occurrence and the different distribution pattern of triterpenic structures endowed with anti-inflammatory activity among the species. Indeed, α- and β-amyrins, β-sitosterol, kaurenoic acid, abietic acid and isopimaric acid were partitioned between the epicuticular depositions and the tissue content. In particular, the highest percentages of all of these compounds were detected in Salvia species from Central and South American regions compared to the native European S. verticillata. Hence, considering the standardized plant growing conditions, these differences can be attributed to intrinsic intra-species variations in the metabolic pathways across the examined sages, rather than to different pedo-climatic and ecological factors.