Essential Oil and Glandular Hairs: Diversity and Roles

Abstract

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.

Improving salinity tolerance in Salvia officinalis L. by foliar application of salicylic acid

“…Microscopic observations on S. officinalis leaves showed the presence of peltate and capitate glands and non-glandular trichomes (protective hairs), which is confirmed and detected by many authors, Es-sbihi et al [18] and Hazzoumi et al [26]. The capitate glands: ("glandular trichomes short-term", as indicated by Werker et al [51]), present the main secretory hairs for some protective substance, release their secretory material shortly after their production and serve to protect young organs.…”

“…Several reports also indicate antigenotoxic and chemopreventive activities of different extracts of S. officinalis L. species. Its essential oil contains cineole, borneol, thujone, camphor, pinene and camphene [18,26]. Like other Lamiaceae, S. officinalis essential oil is located in specialized structures called glandular trichomes [26].…”

“…Its essential oil contains cineole, borneol, thujone, camphor, pinene and camphene [18,26]. Like other Lamiaceae, S. officinalis essential oil is located in specialized structures called glandular trichomes [26]. In Lamiaceae, functionally and according to their mode of secretion, glandular hairs can be classified into two main types, capitate and peltate.…”

The Quality of Greek Oregano (O. vulgare L. subsp. hirtum (Link) Ietswaart) and Common Oregano (O. vulgare L. subsp. vulgare) Cultivated in the Temperate Climate of Central Europe

“…Two different types of these glands were recognized on the epidermis of Origanum species: peltate and capitate glands. The glandular trichomes are built of one basal cell, one stalk cell and a multi-cellular head, where essential oil is synthesized before being transferred to subcuticular area [ 54 , 55 , 56 ]. Svidenko et al [ 56 ] claim that the location of glandular trichomes have valuable taxonomical significance at the species level.…”

Fleeting Beauty—The World of Plant Fragrances and Their Application

“…It occurs when secretory cells are located in some areas of epiderma and secreting fragrant substances through the cell wall. This process is realized by terpenoid glandular trichomes located on the skin surface [ 108 ], like in, e.g., hop plants [ 109 ], peppermint [ 110 ] or through accumulating secreting substances between secretory cells (like in citrus fruits epiderma, where these spaces are formed by the breakdown of secretory cells, or pine resins, which are accumulated in developing regular channel galleries between secretory cells). Interesting is that not only has genetics influenced the chemical composition of aroma compounds in plants but, in basil leaves ( Ocimum basilicum ), it may change after various colours of artificial mulch have been applied during cultivation.…”