Abstract
Lamiaceae contains many species known for their aromatic properties that are produced by the production of essential oils in glandular trichomes. Hyptis is one of the most common genera of Lamiaceae in the Brazilian flora, and includes several species with medicinal value. However, studies on the morphology and functioning of their glandular trichomes are lacking. We analyzed the morphology, histochemistry and ultrastructure of the glandular trichomes in leaves of H. villosa, emphasizing the differential distribution of actin filaments and microtubules in cells secreting hydrophilic and lipophilic compounds. Four morphotypes of glandular trichomes were identified. Total lipid, terpenes, alkaloids, phenolic compounds, proteins and polysaccharides were histochemically detected in all morphotyes. This evidences the mixed nature of the secretions of this species, although there are differences in the prevalence of lipophilic and hydrophilic components among the glandular morphotypes and among the cells of the same trichome. The actin microfilaments are more abundant in cells that secrete mainly hydrophilic compounds, and microtubules predominate in cells that secrete lipophilic compounds. Our results corroborate the correlation between the glandular morphotype and the composition of the secretion produced, with a differential distribution of the cytoskeletal elements according to the prevalence of either hydrophilic or lipophilic substances.
Highlights
Glandular trichomes are epidermal appendices with highly variable morphology and responsible for the production of secretion with economic, medicinal and ecologic values (Ascensão et al 1999; Argyropoulou et al 2010; Tozin et al 2015a)
Our results corroborate the correlation between the glandular morphotype and the composition of the secretion produced, with a differential distribution of the cytoskeletal elements according to the prevalence of either hydrophilic or lipophilic substances
Substances of different chemical categories can be produced by glandular trichomes, and their subcellular features vary according to the substances produced and the form of release of the secretion (Ascensão et al 1995; Ascensão & Pais 1998; Appezzato-da-Glória et al 2012; Naidoo et al 2012; Tozin et al 2015a; Silva et al 2016)
Summary
Glandular trichomes are epidermal appendices with highly variable morphology and responsible for the production of secretion with economic, medicinal and ecologic values (Ascensão et al 1999; Argyropoulou et al 2010; Tozin et al 2015a). The subcellular features of glandular trichomes have been exhaustively described to several species from different families (Ascensão & Pais 1998; Sacchetti et al 1999; Argyropoulou et al 2010; Papini et al 2010; Paiva & Martins 2011; Appezzato-da-Glória et al 2012; Naidoo et al 2012; Amrehn et al 2014; Tozin et al 2015a; Silva et al 2016 and references therein); some important aspects, such as the involvement of the cytoskeletal elements in such secretory process remains poorly studied. Peculiarities on the distribution, arrangement and function of the different glandular morphotypes have been observed in Lamiaceae (Corsi & Bottega 1999) and a correlation between the gland morphology and the composition of secretion has been proposed (Werker 1993; Ascensão & Pais 1998; Corsi & Bottega 1999)
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