Lavandula stoechas subsp. luisieri and L. pedunculata - phytochemical study, micromorphology and histochemistry

Abstract

Extracts of different polarities were obtained from plants of Lavandula stoechas subsp. luisieri and Lavandula pedunculata collected in the Center and Southwest Portugal. In order to have an idea on the possible classes of compounds present in each extract, they were subjected to a preliminary phytochemical screening through thin layer chromatography on silica gel plates, developed in appropriated mixtures of eluents and revealed with the specific reagents. Both taxa showed a hydrophilic and lipophilic chemical composition, being more diverse in L. stoechas subsp. luisieri. The micromorphology and histochemistry of secretory structures were also investigated by light and scanning electron microscopy. The common types of glandular trichomes, found in the Lamiaceae, peltate and capitate type I and II, were identified in each species as well as non-glandular stellate trichomes. In addition to these, L. pedunculata also presented capitate type III trichomes and still more two types of secretory trichomes: i) stellate type with both glandular and non glandular arms and ii) another type of capitate trichome, with a long and broad stalk formed by 2 cells, the basal is conical and much larger than the second, this similar to a ring, which supports a pluricelular head. These types of trichomes appear in the leaves but predominate in the flowers. The histochemical tests confirmed the existence of hydrophilic and lipophilic metabolites in glandular trichomes, except in the peltate hairs of the leaves of L. stoechas subsp. luisieri where only lipophilic secretions prevail.