Glandular Trichomes, Terpenoid Pathways, and Chemotype Interpretation: A Plant-Centered Review of Essential Oil Variability
Radosław Kowalski*
Department of Analysis and Food Quality Assessment, University of Life Sciences in Lublin, Lublin, Poland
* Corresponding Author: Radosław Kowalski. Email: 
(This article belongs to the Special Issue: The Biological Activity of Essential Oils, Volume II)
Phyton-International Journal of Experimental Botany https://doi.org/10.32604/phyton.2026.087213
Received 12 June 2026; Accepted 29 July 2026; Published online 05 August 2026
Abstract
Essential oils (EOs) are most commonly characterized by GC–MS profiles and the relative abundance of dominant constituents. This approach is essential for chemical description and quality control, but it does not fully explain why EO composition differs among species, populations, organs, developmental stages, and growth conditions. Here, EO variability is examined from a focused, plant-centered perspective, with emphasis on terpenoid-rich systems in which glandular trichomes or other secretory structures are documented sites of volatile-metabolite biosynthesis, accumulation, or profile variation. The analysis centers on glandular trichomes as metabolic units, MEP/MVA precursor supply, prenyl diphosphate nodes, terpene synthases, and tailoring enzymes, all of which contribute to EO profile formation and chemotype interpretation. The ecological functions of plant volatiles are treated as a regulatory and interpretative background, with a clear distinction between VOC emissions from living plants, the pool of volatile metabolites stored in secretory structures, and EOs obtained by isolation or distillation. Selected model systems, including examples outside classical EO plants, are used as sources of mechanistic evidence on trichomes, terpenoid pathways, and metabolic regulation, rather than as equivalent examples of standard EO raw materials. The review also addresses the limited comparability of EO bioactivity data, which may result from mixture effects, the contribution of minor constituents, matrix-dependent responses, stereochemistry, and changes induced by stress or biotic pressure. The proposed plant-centered workflow integrates taxonomic authentication, herbarium voucher specimens, organ and phenology data, secretory-structure phenotyping, standardized isolation and analytical protocols, and minimal ecological metadata. Chemotypes should therefore be interpreted not solely on the basis of dominant compounds, but as reproducible chemical profiles embedded in the biological, ecological, and methodological context of the plant material.
Keywords
Essential oils; glandular trichomes; chemotypes; terpenoid biosynthesis; volatile organic compounds; secretory structures; botanical metadata; bioactivity
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