Micropropagação, caracterização dos tricomas glandulares foliares e análise da composição química dos óleos essenciais de Hyptis pycnocephala Benth. (Lamiaceae)

Abstract

Hyptis pycnocephala Benth., is a native and endemic species of Brazil, with distribution in the cerrados of Tocantins and Goiás, in this, it is restricted to the region of Chapada dos Veadeiros. It is known by the traditional Kalunga community as “alecrim-do-campo”, and is used in the treatment of respiratory diseases and gastrointestinal disorders. The species is endangered due to deforestation and fragmentation of its natural habitat, the Cerrado. In this context, the objectives of this work were: to develop a micropropagation protocol, to characterize the leaf micromorphology and the essential oil components of the species. The plant material was collected in the municipality of Cavalcante, GO. H. pycnocephala seeds were decontaminated and used in in vitro germination tests with different concentrations of gibberellic acid (GA3). The seedlings obtained were used to test the media for in vitro establishment, between MS media; MS½; WPM. For multiplication, the influence of cytokinin 6-benzylaminopurine (BAP) and different concentrations of auxin naphthaleneacetic acid (NAA) for rooting was tested. For acclimatization, substrates with different amounts of gully soil, commercial substrate and sand were tested. For the micromorphological analyses, the usual techniques of plant anatomy were used. The essential oil was extracted by hydrodistillation in a Clevenger type apparatus and the constituents were identified by gas chromatography coupled to mass spectrometry. In vitro germination has better results with 144.5 µM GA3. For in vitro establishment, the WPM medium proved to be the best. For shoot multiplication, the use of 6.66 µM of BAP is indicated and for rooting, the use of auxins is not necessary. For acclimatization, there were no significant differences for the substrate, however, roots with less than 1 cm provided lower performances. A morphological and histochemical diversity was observed in the glandular trichomes present in the leaves of H. pycnocephala, both in field and micropropagated plants. Two types have been identified: peltado and capitate. Among the capitates, six types have been described. Different essential oil yields and chemical composition were obtained between leaves collected in the field when compared to micropropagated ones. Essential oils were mainly made up of monoterpenes, sesquiterpenes. The major compounds are endo-fenchol, α-pinene and β-caryophyllene both in samples from micropropagation and those collected in nature. Plants from in vitro cultivation showed higher yields compared to other samples and new compounds such as Dauca-4 (11), 7-diene and δ-3-Carene and increased levels of β-caryophyllene and endo-fenchol. These promising results will support future research on medicinal properties and commercial applications, in addition to contributing to the conservation of H. pycnocephala.