Citral chemotypes Cinnamomum camphora (C. camphora) and Cinnamomum bodinieri (C. bodinieri) are promising industrial plants that contain abundant citral. For a more in-depth study, their significant biological effect, the chemical composition and antioxidant capacity of essential oils of citral-rich chemotype C. camphora and C. bodinieri (EOCC) were determined in the present study. The EOCC yield, obtained by hydro-distillation and analyzed by gas chromatography–mass spectrometry (GC-MS), ranged from 1.45–2.64%. Forty components more than 0.1% were identified and represented, mainly by a high content of neral (28.6–39.2%), geranial (31.8–54.1%), Z-isocitral (1.8–3.2%), E-isocitral (3.2–4.7%), geraniol (1.3–2.6%) and caryophyllene (0.6–2.4%). The antioxidant properties of EOCC were estimated by DPPH, ABTS and FRAP methods. As our results indicated, the antioxidant activity was significantly correlated to oxygenated monoterpenes. The variety of C. bodinieri (N7) presented the best antioxidant profile, given its highest inhibition of DPPH radical (IC₅₀ = 6.887 ± 0.151 mg/mL) and ABTS radical scavenging activity (IC₅₀ = 19.08 ± 0.02 mg/mL). To the best of our knowledge, more than 88% citral of C. bodinieri was investigated and the antioxidant properties described for the first time. Considering high essential oil yield, rich citral content and high antioxidant activity, the N7 variety will be a good candidate for pharmaceutical and cosmetic development of an improved variety.

The citral-type is the most common chemotype in Cinnamomum bodinieri Levl (C. bodinieri), which has been widely used in the daily necessities, cosmetics, biomedicine, and aromatic areas due to their high citral content. Despite of this economic prospect, the possible gene-regulatory roles of citral biosynthesis in the same geographic environment remains unknown. In this study, the essential oils (EOs) of three citral type (B1, B2, B3) and one non-citral type (B0) varieties of C. bodinieri were identified by GC-MS after hydrodistillation extraction in July. 43 components more than 0.10% were identified in the EOs, mainly composed of monoterpenes (75.8–91.84%), and high content citral (80.63–86.33%) were identified in citral-type. Combined transcriptome and metabolite profiling analysis, plant-pathogen interaction(ko04626), MAPK signaling pathway-plant(ko04016), starch and sucrose metabolism(ko00500), plant hormone signal transduction(ko04075), terpenoid backbone biosynthesis (ko00900) and monoterpenoid biosynthesis (ko00902) pathways were enriched significantly. The gene expression of differential genes were linked to the monoterpene content, and the geraniol synthase (CbGES), alcohol dehydrogenase (CbADH), geraniol 8-hydroxylase-like (CbCYP76B6-like) and 8-hydroxygeraniol dehydrogenase (Cb10HGO) were upregulated in the citral-type, indicating that they were associated with high content of geraniol and citral. The activities of CbGES and CbADH in citral type were higher than in non-citral type, which was corroborated by enzyme-linked immunosorbent assay (ELISA). This study on the accumulation mechanism of citral provides a theoretical basis for the development of essential oil of C. bodinieri.

The citral chemotype of Camphora officinarum Nees ex Wall. is a promising industrial plant that contains an abundance of citral, which is widely used in medical, chemical, food, and other fields. For a more in-depth exploration, the dynamic characteristics of its essential oil (EO), oil compositions (OCs), and oil cells during leaf development were determined in the present study. The leaf phenotype changed rapidly from the 1st to the 4th week after leaf bud germination. The oil yield (OY), obtained via supercritical carbon dioxide extraction, reached the highest value of 2.82% ± 0.20% in the 12th week. Leaf development is a prerequisite for the production of EO, and the difference in the OY was not significant after leaf maturation. The OCs, analyzed using gas chromatography–mass spectrometry (GC-MS), mainly included aldehydes, alcohols, and hydrocarbons. Different types of compounds accumulated differently during leaf development: the highest relative content of alcohol in the OCs was 30.18% in the 2nd week, while that of aldehyde was 76.11% in the 6th week. In total, 130 OCs were detected, and two isomers of citral, namely, geranial and neral, had the highest relative levels of 51.12% (12th week) and 28.63% (6th week), respectively. The OY was closely related to the developmental stage of the oil cells. In the 1st–2nd weeks, the oil cells were mostly in the non-essential oil stage and essential oil-forming stage, with a lower OY; oil cells reached saturation in the 12–24th weeks, with a higher OY. Transmission electron microscopy showed that osmium droplets were present in large quantities during leaf development and gradually integrated into the vacuoles, finally making the vacuoles become oil bladders for oil storage. In conclusion, EO may have new uses due to the different OCs in leaf development; additionally, the microscopic changes in C. officinarum provide a reference for the cellular mechanism of EO accumulation.

Camphora officinarum Nees ex Wall ( C. officinarum ), a citral-rich aromatic plant, is recognized as an unrivalled natural source of citral for spice production. Its large-scale cultivation in China via the sustainable coppice-rotation system has markedly revitalized rural economies. Nevertheless, the genetic basis driving its prolific citral accumulation remains elusive. We conducted an integrated transcriptomic and metabolomic analysis comparing three citral type accessions (C1, C2, C3) with a non-citral type control (C0). Metabolomic profiling identified 904 leaf metabolites, with terpenoids representing the most abundant class (19.49%). Strikingly, GC-MS analysis unveiled a monoterpene-dominated essential oil composition in citral type C. officinarum leaves , characterized by four dominant constituents: geranial (36.9%-44.7%), neral (30.7%-34.1%), E-isocitral (2.2%-2.9%), and Z-isocitral (1.5%-2.1%). Integrated transcriptomic and metabolomic analysis highlighted critical key genes, acetyl-CoA C-acetyltransferase ( CoAACT ), hydroxymethylglutaryl-CoA synthase ( CoHMGS) , hydroxymethylglutaryl-CoA reductase ( CoHMGR ), phosphomevalonate decarboxylase ( CoMVD ), 1-deoxy-D-xylulose-5-phosphate synthase ( CoDXS ), geranylgeranyl diphosphate synthase, type Ⅲ ( CoGGPS) , farnesyl diphosphate synthase ( CoFDPS ) showed elevated expression, enhancing precursor availability. The geraniol synthase ( CoGES ) and alcohol dehydrogenase ( CoADH ) involved in citral synthesis were significantly up-regulated in citral type C. officinarum . These findings demonstrate that the quantitative disparities in terpenoid distribution and concentration collectively define the species’ unique aromatic identity, underscoring chemotype-specific metabolic regulation mechanisms, while also screening key genetic determinants of citral biosynthesis preliminarily, thereby laying the groundwork for precision breeding programs in aromatic C. officinarum .

To explore the patterns of essential oil synthesis and the optimal harvesting period of citral-type Camphora officinarum Nees ex Wall (C. officinarum) at different growth stages, three varieties (C1, C2, C3) from the citral-type C. officinarum coppice were taken as research objects. During the leaf growth cycle from February 2022 to January 2023 (12 periods in total), their morphological indicators, biomass, essential oil yield, chemical components, and output were determined. As a natural monoterpenoid widely used in the food additive, pharmaceutical intermediate, and flavor/fragrance industries, citral-related research is of great significance for improving the breeding value of citral-type C. officinarum germplasm resources. The results showed that: (1) The leaf area, total biomass, and leaf-branch ratio of the three varieties all reached the maximum in Period I (late August, full fruit stage), among which the leaf biomass and total biomass of C1 were significantly higher than those of C2 and C3. (2) The essential oil yield based on dry weight of leaves (0.53–2.79%) was significantly higher than that of branches (0.48–0.7%). Citral (geranial and neral) was the main component of the essential oil; the citral contents in C1 and C2 were the highest in Period G (late June, early fruit stage) (78.38% and 71.78%, respectively), while that in C3 peaked in Period F (late May, late flowering stage) (70.46%). (3) The total essential oil yield reached the peak in Period I, with C1 being significantly higher at 20.19 ± 1.88 g/plant than C2 (13.8 ± 0.61 g/plant) and C3 (16.47 ± 0.87 g/plant). Comprehensive analysis indicated that C1 was identified as the top-performing cultivar among citral-type C. officinarum, and July–August was the optimal harvest period. During this period, both essential oil yield and citral content could be balanced to maximize economic benefits.

Citral-type Camphora officinarum (C. officinarum) exhibits high economic value due to its branch and leaf essential oil enriched with citral, yet the low natural concentration of this compound necessitates urgent strategies to enhance yield and quality. Methyl jasmonate (MeJA), a recognized safe elicitor, stimulates aromatic compound accumulation in plants and promotes monoterpene synthesis in C. officinarum suspension cells. However, it remained unclear whether foliar MeJA application enhances monoterpene biosynthesis in C. officinarum. This study evaluated the effects of near-harvest foliar MeJA application at gradient concentrations 0 μmol/L (control, M0), 100 μmol/L (M100), 250 μmol/L (M250), and 500 μmol/L (M500) on growth, oil gland morphology, and essential oil composition in citral-type C. officinarum. The results demonstrated that: M100 treatment significantly increased plant height, branch biomass, leaf biomass, and total biomass compared to the control M0. M250 treatment induced structural modifications in oil cells, enlarging their diameter and increasing density, resulting in an 11.83% increase in essential oil yield per unit fresh leaf weight. Both M100 and M250 treatments enhanced citral content by 3.6% and 3.31%, respectively, while total essential oil production surged by 12.31% (M100) and 15.46% (M250). Principal component analysis (PCA) collectively demonstrated that 100–250 μmol/L MeJA (M100/M250) represented the optimal induction concentration for enhancing essential oil yield and promoting citral synthesis, whereas 500 μmol/L (M500) induced detrimental osmotic stress. These findings demonstrate that MeJA serves as a safe agricultural regulation approach for enhancing essential oil yield and citral content, offering valuable insights for other aromatic plant species.