Influence of environmental factors on the volatile composition of two Brazilian medicinal plants: Mikania laevigata and Mikania glomerata.

Abstract

Mikania laevigata Sch.Bip. ex Baker and Mikania glomerata Spreng. are medicinal plants popularly known as guaco, used for inflammatory diseases of the respiratory system, included in pharmaceutical formularies and often used without distinction. However, several studies show that the chemical composition varies between these species, as well as in plants are subjected to different environmental stresses. Few studies have been carried out with the volatile compounds of guaco, even less about the changes in volatile composition due to abiotic variation. The aim of this work was to evaluate how volatile compounds vary according to the seasons and at different times of the day and if these compounds are influenced by the variations in the growth conditions such as: temperature, luminosity and water. The headspace volatiles of the leaves were sampled by solid phase micro extraction and analyzed by gas chromatography-mass spectrometry. Untargeted metabolomic analysis of the resulting chromatograms and chemometrics was applied. The chemical profile of the volatiles of M. laevigata and M. glomerata were different; being clearly separated in the exploratory grouping analyzes (PCA), followed by analysis of variance of the marker compounds of both species. Only M. laevigata contained coumarin, considered to be the chemical marker of both species and to be responsible for the therapeutic activities. There was no significant difference between the morning and afternoon collections of either species. Coumarin, α-pinene and bicyclogermacrene were more intense in the volatiles of M. laevigata throughout the year and responsible for grouping the samples of this species. For M. glomerata, hexanal and 2-hexenal were responsible for grouping the samples and were more intense in all months. The growth conditions tested affected the intensity of specific compounds in the chromatograms. Some compounds were less intense with the increase of the temperature and in the plants subjected to full sunlight. However, certain volatile compounds-such as pinenes-were more intense in plants suffering drought. The variation in composition between species of guaco was greater than those observed in the seasonal and cultivation studies, indicating that these species cannot be used indistinctly.