Glandular trichomes of Coleus amboinicus Lour. and the effect of developmental stage on leaf headspace volatile composition
Guilherme Perez Pinheiro, Diego da Silva Graciano, Juliana Lischka Sampaio Mayer, Leandro Wang Hantao, Alexandra Christine Helena Frankland Sawaya
Abstract
Coleus amboinicus Lour. is a perennial shrub frequently used in folk medicine for the treatment of cough, sore throat and other respiratory disorders. Although being one of the best chemically documented Lamiaceae species, little is known about the glandular trichomes that secrete essential oils in this species and the effects of leaf development on the volatile composition. We characterized herein the different types of glandular trichomes of C. amboinicus and, using headspace solid phase microextraction coupled to gas chromatography (HS-SPME-GC–MS), we evaluated the chemical composition of leaves in different stages of development. Two main categories of glandular trichomes were observed: short-stalked and long-stalked capitate trichomes, two types of each were described whilst no peltate trichome was observed. The chromatographic analysis showed that carvacrol was the main component of the volatile profile, followed by o-cymene, γ-terpinene, (E)-caryophyllene and α-trans-bergamotene. The proportion of mono- and sesquiterpenes changed as the leaves expanded, every volatile component varied significantly (p < 0.05) such as an increase in carvacrol area percentage and decrease in (E)-caryophyllene and γ-terpinene, suggesting that expanding leaves are chemically distinct to the fully expanded ones. These results provide new insights about C. amboinicus morphoanatomy and phytochemistry, further research is required to establish the effects of leaf developmental stage on volatile composition and glandular trichome distribution in other Lamiaceae species.