The main difference between glandular and non-glandular trichomes is that glandular trichomes have a glandular head and secrete secondary metabolites, whereas non-glandular trichomes do not have a glandular head.
Trichomes are unicellular or multicellular appendages that are extensions of the above-ground epidermal cells in plants. These appendages help in the development of plants and are present in a wide variety of species of plants. Trichomes act as natural barriers against natural hazards, hence providing protection to plants. These natural hazards include UV radiation, pathogen attacks, excessive transpiration, seed spread, and seed protection. Moreover, trichomes are used in various industries, including the tea and textile industries. They also have nutritional, therapeutic, and medicinal benefits. Trichomes can be divided into glandular and non-glandular trichomes depending on the morphology and secretion ability.
Key Areas Covered
1. What are Glandular Trichomes
– Definition, Structure, Function
2. What are Non-Glandular Trichomes
– Definition, Structure, Function
3. Difference Between Glandular Trichomes and Non-Glandular Trichomes
– Comparison of Key Differences
Key Terms
Capitate Trichomes, Glandular Trichomes, Non-Glandular Trichomes, Peltate Trichomes, Trichomes
What are Glandular Trichomes
Glandular trichomes are specialized hair cells present on the surfaces of vascular plants. Multicellular glandular trichomes are epidermal outgrowths that have a head made of cells with the ability to secrete and store large quantities of specialized metabolites. They basically act like cell factories. These glandular trichomes are considered to have elaborate, highly organized, and polarized cells. Glandular trichomes are present in approximately 30% of vascular plant species. In fact, one can observe the presence of both glandular and non-glandular trichomes in a single plant.
There are two main types of glandular trichomes; the are capitate and peltate, depending on the stalk length and size of the head. Capitate trichomes have a stalk that is more than half of the head height. On the other hand, peltate trichomes have a short stalk with a large secretory head made of 4 to 18 cells. These cells are arranged in one or two concentric circles. The stalks are unicellular or bicellular. Capitate trichomes have a vast variety, depending on the length of the stalk, the number of cells in the stalk, the morphology of the glandular head, and the pattern of secretion. Hence, there are several different types of capitate trichomes.
Glandular trichomes secrete specialized metabolites. For example, trichomes release terpenoids, flavonoids, methyl ketones, and acyl sugars. Moreover, these trichomes have been studied mostly to decode the biochemical pathways of the compounds they produce and secrete.
What are Non-Glandular Trichomes
The main feature of non-glandular trichomes is the absence of a glandular head, unlike in glandular trichomes. These trichomes often take a star shape. Non-glandular trichomes can either be unicellular or multicellular. They have a thin apex and can either be branched or not. Furthermore, they cover a wide area of the surface of plant organs.
Non-glandular trichomes do not produce, liberate, or store biologically active chemical compounds. But they protect the plants from biotic and abiotic stress-causing factors like low humidity, high temperatures, and radiation from the sun. Additionally, they retain an air film on the surface of the aquatic plants. The presence of these trichomes also helps with resistance to herbivore attacks.
During the early stages of development, non-glandular trichomes are very much similar to glandular trichomes, just like the apical cells, which are balloon-like and contain numerous phenolics. At later developmental stages, the phenolics are transferred to the cell wall of the trichomes during the secondary wall thickening.
Difference Between Glandular and Non-Glandular Trichomes
Definition
Glandular trichomes are specialized hair-like structures found on the surface of many plants that produce and secrete various substances, while non-glandular trichomes are small, hair-like structures that are found on the surface of many plants.
Presence of a Glandular Head
Glandular trichomes have a glandular head, whereas non-glandular trichomes do not have any glandular head.
Function
While glandular trichomes secrete secondary metabolites that are important for defense, protection, and pollination, non-glandular trichomes provide physical protection to plants against biotic and abiotic stresses.
Secretion
Glandular trichomes secrete specialized metabolites like terpenoids, flavonoids, methyl ketones, acyl sugars, and terpenoids, whereas non-glandular trichomes do not produce, liberate, or store biologically active chemical compounds.
Structure of the Apex
In glandular trichomes, a glandular head is present at the apex, whereas, in non-glandular trichomes, a thin apex is present without a head.
Conclusion
Trichomes are unicellular or multicellular appendages that are extensions of the above-ground epidermal cells in plants. There are two main types of trichomes depending on the morphological structure and function. They are glandular trichomes and non-glandular trichomes. The main difference between glandular and non-glandular trichomes is that glandular trichomes have a glandular head and secrete secondary metabolites, whereas non-glandular trichomes do not have a glandular head.
Reference:
1. Santos Tozin, L. R., de Melo Silva, S. C., & Rodrigues, T. M. (2016). Non-glandular trichomes in Lamiaceae and Verbenaceae species: Morphological and histochemical features indicate more than physical protection. New Zealand Journal of Botany, 54(4), 446–457.
2. Glas, J., Schimmel, B., Alba, J., Escobar-Bravo, R., Schuurink, R., & Kant, M. (2012). Plant glandular trichomes as targets for breeding or engineering of resistance to herbivores. International Journal of Molecular Sciences, 13(12), 17077–17103.
Image Courtesy:
1. “Violet glandular trichomes” By Ivan Bachev – Own work (CC BY 4.0) via Commons Wikimedia
Leave a Reply