Ontogenetic regulation of metabolite dynamics in Thymbra capitata : temporal reconfiguration of essential oils and antioxidant capacities across sequential harvests

Uğur Tan

Abstract

Thymbra capitata is a Mediterranean aromatic shrub that is extensively used to produce essential oils and phenolic antioxidants. Despite having a chemical profile that varies with phenological stage, most previous studies have been based on single or few harvests, giving only a fixed perspective of metabolism. As a result, the ontogenetic control of essential oil production, monoterpene formation, and antioxidant-related metabolism throughout the entire vegetation cycle has been poorly clarified. The aim of this study was to measure such changes in these characteristics over sequential periods of harvest to determine developmental trade-offs between essential oils and antioxidants under natural conditions. Plant samples were collected bi-weekly (H1–H14) from late winter through late summer. Essential oils were extracted by hydrodistillation and their composition analyzed by gas chromatography–mass spectrometry (GC-MS). The Folin-Ciocalteu, Aluminium chloride colorimetric, 2,2-diphenyl-1-picrylhydrazyl (DPPH), and 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays were used to measure total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activities. Mixed-effects models with unequal variance structures were employed in the analysis of data, and principal component analysis was used to examine multivariate patterns in essential oil composition. The content of essential oils showed high ontogenetic modulation, increasing from 1.38% at the initial harvest to a maximum of 5.97% at flowering (H11) with a 333% increase, and followed by a 46% decrease during post-flowering senescence. The highest levels of TFC were reached in initial harvest as 225.83 mg rutin g −1 dry weight (DW) at H2 and decreased by 49% at the final harvest. The TPC ranged between 41.58 mg gallic acid equivalents (GAE) g −1 DW and 65.47 mg GAE g −1 DW, with the highest value occurring in the middle of the season. DPPH activity reached 64.47 mg Trolox equivalent antioxidant capacity (TEAC) g −1 DW at H5 and dropped to a minimum value at H13–H14. The essential oil composition also changed with time, with carvacrol decreased from 81.2% at H1 to 64.6% at H14, and p-cymene (cymol) and γ-terpinene increased from 2.6% to 13.4% and 3.8% to 9.3% respectively. These findings demonstrate that phenolic-related antioxidants and terpenoid volatiles in T. capitata undergo coordinated, developmentally driven changes that result in a quantitative trade-off between these metabolite groups. Early harvest maximizes the levels of antioxidants and phenolic monoterpenes, whereas flowering and late harvests favor higher essential oil with a hydrocarbon-rich profile. Understanding these temporal metabolic patterns provides a practical background for optimizing harvest timing to achieve specific industrial, nutritional, or therapeutic objectives.

Source: semanticscholar · PDF

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