Rupture of glandular trichomes in Ocimum gratissimum leaves influences the content of essential oil during the drying method

Medicinal and aromatic plants are commonly sold dried; however, it is necessary to understand the effects different drying methods have on these materials, to ensure their efficiency and quality. Ocimum gratissimum L., Lamiaceae, is an aromatic plant whose essential oil is stored in glandular trichomes. This study aimed to confirm the effects of different drying temperatures and methods of O. gratissimum leaves on trichome integrity and essential oil content. Leaves dried in a forced ventilation oven at 60ºC display damaged trichomes and a reduction in the essential oil content. The different drying methods (oven, dehumidification and air drying) were not identified to elicit changes in the essential oil content or damage to trichomes. All of the drying methods showed a reduction in fungal contamination in a logarithmic cycle.

Light affects Varronia curassavica essential oil yield by increasing trichomes frequency

Light can act on essential oil yield directly on synthesis of secondary metabolites, or indirectly on plant growth. Varronia curassavica Jacq., Boraginaceae, is a native medicinal species from Brazil known as “erva-baleeira”, with anti-inflammatory activity related to its essential oil. Despite pharmacological evidences of this species and its economic importance for herbal medicine production, little is known about the effect of light on growth and essential oil production. This study aimed to analyze the influence of different irradiances on growth, frequency of trichomes, essential oil yield and composition of V. curassavica. The irradiance affected plant growth, but no significant alteration on leaf biomass was detected. The increase in essential oil content under higher irradiance reflected on essential oil yield, and is associated with higher frequency of glandular, globular trichomes. The essential oil composition, rich in caryophyllene derivatives was affected by irradiance, but α-humulene, the constituent of pharmaceutical interest, remained unchanged.

Light intensity on growth, leaf micromorphology and essential oil production of Ocimum gratissimum

Light conditions can promote the growth and development of plants and contribute to increase the essential oil production of commercially cultivated medicinal and aromatic species. In view of the great importance of Ocimum gratissimum L., Lamiaceae, as an aromatic plant, the objective of this work was to determine the effect of light intensities (approximately 4, 7, 11 and 20 mol m-2 d-1) on growth, foliar micromorphology, essential oil content, yield and chemical composition of O. gratissimum. Biomass production of different organs, root:shoot ratio and leaf mass per area were found to linearly increase with increased light availability, whereas stem dry matter fraction, number of leaves, leaf area and plant height have increased up to 10 mol m-2 d-1 and decreased from this value. The tector trichomes density increased with increased light availability, but there was no effect of light treatments on the glandular trichomes density and essential oil content. Regardless of the light level, the major component of the essential oil was eugenol. The essential oil yield per plant increased linearly with light intensity as a direct effect of increased leaf biomass under similar conditions.