Glandular trichomes on aerial and underground organs in Chrysolaena species (Vernonieae – Asteraceae): Structure, ultrastructure and chemical composition

Although the occurrence of glandular trichomes is frequently reported for aerial vegetative organs, many questions still remain opened about the presence of such trichomes in underground systems. Here, we present, for the first time, a comparative study concerning the structure, ultrastructure and chemical aspects of both, the aerial and underground glandular trichomes of two different Chrysolaena species, C. obovata and C. platensis. Glandular trichomes (GTs) were examined using LM, SEM, and TEM and also analyzed by GC–MS and HPLC coupled to UV/DAD and HR-ESI-MS (HPLC–UV–MS). In both aerial (leaf and bud) and underground (rhizophore) organs, the GTs are multicellular, biseriate and formed by five pairs of cells: a pair of support cells, a pair of basal cells, and three pairs of secreting cells. These secreting cells have, at the beginning of secretory process, abundance of smooth ER. The same classes of secondary metabolites are biosynthesized and stored in both aerial and underground GTs of C. platensis and C. obovata. These GTs from aerial and underground organs have similar cellular and sub-cellular anatomy, however the belowground trichomes show a higher diversity of compounds when compared to those from the leaves. We also demonstrate by means of HPLC–UV–DAD that the sesquiterpene lactones are located inside the trichomes and that hirsutinolides are not artifacts.