Leaf secretory tissues in Myrsine coriacea and Myrsine venosa (Primulaceae): ontogeny, morphology, and chemical composition of essential oils

Abstract

Secretory structures are an outstanding feature in Primulaceae (Ericales). Such structures are known for their taxonomical and medicinal importance. However, a detailed morphological study of the secretory structures in Primulaceae has been neglected. Selected species for this study belong to Myrsine, a widely distributed genus in Brazil, popularly known as “capororoca”. In this study, we aimed to elucidate the ontogenesis of the secretory structures in the leaves of Myrsine coriacea (Sw.) R. Br. ex Roem & Schult. and Myrsine venosa A.DC. and report, for the first time, on the composition of their essential oils. The following secretory structures are found in M. coriacea and M. venosa: idioblasts, glandular trichomes, and secretory cavities. The development of all secretory structures, which is asynchronous, occurs during leaf expansion and differentiation; therefore, in leaf primordia, the same type of secretory structure could be observed at different stages of differentiation. By the complete expansion of leaf primordia, all secretory structures have reached their full size. Idioblasts are derived from both protodermal and ground meristem cells and they secrete mucilage or phenolic compounds. The glandular trichomes can be peltate, as found in both species, or branched, as found only in M. coriacea. Trichomes are initiated by the enlargement of protodermal cells, followed by their division, and they are completely formed by the end of leaf expansion. Secretory cavities are schizogenous and originated from ground meristem cells. Major components from M. coriacea essential oils were β-elemene, γ-muurolene, and α-cadinene, while the major components of M. venosa essential oils were β-caryophyllene, γ-muurolene, and δ-cadinene.