Essential Oil and Glandular Hairs: Diversity and Roles

The accumulation of essential oils in plants is generally limited to specialized secretory structures, namely, glandular trichomes (hairs) which are multicellular epidermal glands, found in some families such as Lamiaceae, Asteraceae, and Solanaceae, and which secrete terpenes in an extracellular cavity at the apex of the trichome. Storage of terpenoids in these structures can also be used to limit the risk of toxicity to the plant itself. The morphology of these structures varies according to the conditions of irrigation and also according to the toxicity of intracuticular contents and can be changed with the phenology of the plant. The secretory glands of aromatic plants come in different shapes and sizes, in order to ensure a specific function. This function consists mainly in the protection of different plant organs and the attraction of pollinators. Some scientist classified these glands into peltate hairs and capitate hairs, based on morphological criteria; however, others classified them into short-term glands and long-term glands, based on the mode of secretion. Short-term glands are glands that secrete rapidly to protect young organs. The long-term glands are glands in which the secretory substance accumulates gradually in the subcuticular space and play a role in the protection of mature organs such as the flower, as well as in pollination. According to this definition, he inferred that the capitate hairs are the short-term glands, while the peltate hairs are long-term glands. The difference between these two types of glands consists several aspects like structure, mode of secretion, and timing of secretion. In this object, this chapter includes some microscopic observation to glandular hairs and their combination with mode of secretion, nature of contents, and phenology of plant to give a good comprehension and classification

Effect of the exogenous application of abscisic acid (ABA) at fruit set and at veraison on cell ripeness of olives Olea europaea L. and the extractability of phenolic compounds in virgin olive oil

Abstract Background The effect of the exogenous application of abscisic acid (ABA) at the fruit set and veraison on the cell maturity of the olive Olea europaea L. and on the extractability of phenolic compounds (PC) in the virgin oil olive was studied. Methods The ABA was sprayed on olive trees of the Moroccan Picholine variety at a concentration of 10−3 mg/l, some olive trees are treated at fruit set stage and other olive trees are treated at veraison stage. The effects of these treatments were evaluated by fruit yield and determination of the date of veraison and ripening period of the olives. The extractability of olive oil and diffusion of PC in the latter as well as the weakening of the parietal structures are also estimated. Results and discussion The application of ABA at fruit set causes a decrease in the production of fruit about 50% and precocity of ripening estimated 45 days. At this stage, comparing with the control in the same period, there was a significant accumulation of fat in olives, an increase in oil extractability and a significant improvement in the diffusion of PC in oils. The treatment of the olives by the ABA at veraison has no effect on yield. However, we observe physiological and biochemical changes to be identical during the treatment by ABA at veraison but smaller than that at fruit set. Graphical abstract Effect of exogenous application of ABA on the ripening of Moroccan Picholine olives and on the extractability of the fat and phenolic compounds in virgin olive oil. ↑, Increase; ∼, environ

Effect of ethephon application on the cellular maturity of Olea europaea L. and on the extractability of phenolic compounds in virgin olive oil

Abstract Background The effect of the ethephon application at fruit set and veraison on cell maturity of Olea europaea L. olives and on the extractability of phenolic compounds (PC) in virgin olive oil has been studied. Methods The ethephon was sprayed on olive trees of the Moroccan Picholine at the fruit set stage and on other olive trees at the veraison stage at a concentration of 100 mg/L. The effect of these treatments was evaluated by the fruit yield and the determination of the period of olives growth and ripening. The extractability of the olive oil and the diffusion of the PCs in the fat as well as the embrittlement of the parietal structures are also monitored. Results and conclusions A chemical thinning is entrained out by ethephon when applied at fruit set (16%) or veraison (12%). It also results in precocious ripening of fruits treated at fruit set (about 2 weeks) and a precocity of the harvest similar to that induced in olives treated at veraison (estimated at 6 weeks). At this stage, a significant increase in the fat accumulation (more than 26 g/100 g in the olives treated compared to 7.7 g/100 g olive pulp in the control) and quantities of extracted oils (87 and 83%, respectively, in the olives treated at fruit set and those treated at veraison compared to 70% in the control) as well as a significant improvement in the extractability of the diffusible PCs in these oils at maturity (540 and 590 mg/kg, respectively, in the treated olives at fruit set and those treated at veraison compared to 216 mg/kg in the control oil)

Effect of gibberellic acid (GA), indole acetic acid (IAA) and benzylaminopurine (BAP) on the synthesis of essential oils and the isomerization of methyl chavicol and trans-anethole in Ocimum gratissimum L

Basil (O. gratissimum L) is a aromatic and medicinal plant widely used in traditional medicine in Morocco. The aim of this work was to study the effect of three plant growth regulators gibberellic acid (GA), indole 3-acetic acid (IAA) and benzylaminopurine (BAP) on the content and composition of essential oils of this plant, especially on the main compound (methyl chavicol) and its isomer (the trans-anethole). The results showed a wide variation on yield, content and range of the molecule constituent of oil, with a balance of appearances and/or disappearances of a few molecules. GA caused a slight decrease in the oil yield (0.2%), but it increased the diversity of compounds (17 molecules) with the appearance of four new compounds (naphthalene, camphor, germacrene-D, and ledene) and disappearance of (β cedrene, azulene). This variation also caused a very important decrease in the main compound (methyl chavicol) and increases its isomer (trans-anethole). IAA and BAP caused an increase in the yield of essential oil (0.30% and 0.32% respectively) without much influence on the main compounds, but with some change in the composition such as the appearance of (germacrene-D) and the disappearance of (aristolene)

Effect of arbuscular mycorrhizal fungi and water stress on ultrastructural change of glandular hairs and essential oil compositions in Ocimum gratissimum

Abstract Background The objective of this work is to study the influence of arbuscal mycorrhizal fungi (Glomus intraradices) and water stress on the ultrastructural change of basil glandular hair and also on the essential oil synthesis, especially on the isomerization of the two main compounds methyl chavicol and trans-anethole. Results The results of this study show that mycorrhization increases the yield of essential oils, with a maximum recorded in mycorrhizal stressed plants (0.33%) and a minimum among non-mycorrhizal unstressed plants (0.22%). Oxygenated monoterpenes represent the main family of essential oils. Furthermore, the chemical composition of these essential oils changed under the condition in which the plant is. However, the main compound methyl chavicol was found to be at maximum concentration (93%) in mycorrhizal stressed plants and minimum in non-mycorrhizal stressed plants (84%). Contrariwise, its isomer trans-anethole reached the maximum (8%) among non-mycorrhizal non-stressed plants and minimum (2%) in non-mycorrhizal stressed plants. Conclusion Ocimum gratissimum L. leaves showed the presence of two types of peltate glands: the first one with 4 secreting cells and the second with 8 secreting cells. The diameter of these glands changed with the hydric state of plants; in the absence of mycorrhization, stress causes a decrease in the extracellular cavity diameter of glandular trichomes and their deflation which would cause a concentration of essential oil in the glands. Graphical abstract Effect of arbuscular mycorrhizal fungi and water stress on essential oil yield and compositions by the change in some endogenous plant growth regulators and glandular hairs morphology and density in Ocimum gratissimu