The Structural Peculiarities of the Leaf Glandular Trichomes: A Review

Abstract

Leaf glandular trichomes are multicellular secretory structures that arise from protodermal cells. They are characterized by a diverse form, localization, density, and composition of secreted substances. Formation of the glandular trichomes is caused by the need to protect plants from various biotic and abiotic factors, including herbivorous insects, fungi, pathogens, extensive light, UVB radiation, or high temperature. The main feature of the glandular trichomes is an ability to synthesize and accumulate the various compounds of primary and secondary metabolism. Morphology, development, ultrastructural characteristics of the cells producing the secondary compounds, content of the secretory products, as well as mechanisms of secretion are discussed in this chapter.

Ultrastructural Alterations in Cells of Sunflower Linear Glandular Trichomes during Maturation

“…In the pre-secretory stage, it was very rich in plasma, but contained no or only few plastids compared to the adjacent glandular cells. The high amount of endoplasmic reticulum and Golgi vesicles (Figure 3) is described as typical for a secretory cell [3]. The compounds appeared to be predominantly produced by glandular cells beneath the apical cell.…”

“…Whether rupture of the cuticle is necessary to release secreted compounds is unknown and requires further studies. However, alternative modes such as micro-channels [3] or minute pores in the intact cuticle for the release of volatile metabolites [21] are thinkable as well for the release of volatile compounds.…”

“…Plant trichomes are highly essential structures of the epidermis which have numerous physical and physiological functions in various developmental stages of the plant's life cycle [1,2]. Particularly trichomes with glandular activity have attracted scientific interest due to their ability to produce and spread a multitude of highly specialized metabolites for organismic interaction and their suitability for human use [3]. Glandular trichomes occur in nearly all plant families with a broad variety of different morphological types [2], which in some cases such as in Lamiaceae, Solanaceae or Asteraceae, have gained model character for investigation of developmental and biosynthetic processes [4][5][6].…”

Cannabis Glandular Trichomes: A Cellular Metabolite Factory

“…Glandular trichomes, which arise from the epidermis on vegetative and reproductive organs, can be generally divided into secretory and non-secretory types with the former being able to secrete substances ( Tian et al, 2017 ). Both the morphologies and metabolic secretions of trichomes are consistent within a plant species, and some species have different trichome morphs on the same plant organ ( Muravnik, 2020 ). Secreted compounds, including THCA ( Sirikantaramas et al, 2005 ), can be toxic to plant cells; therefore, metabolite storage in the cavity of the glandular head affords protection to the plant ( Sirikantaramas et al, 2008 ).…”

“…While different glandular trichome morphs invoke different storage strategies, the architecture of the morph and cavity position in relation to the secretory cells determine secretion direction ( Tissier et al, 2017 ). The molecular details surrounding the development of glandular trichomes and their secretions are beyond the scope of this article, and we refer to in-depth reviews by Muravnik (2020) and Tian et al (2017) .…”