Diversity of essential oil glands of clary sage (Salvia sclarea L., Lamiaceae)

Exploring the co-operativity of secretory structures for defense and pollination in flowering plants

MAIN CONCLUSION

In flowers multiple secretory systems cooperate to deliver specialized metabolites to support specific roles in defence and pollination. The collective roles of cell types, enzymes, and transporters are discussed. The interplay between reproductive strategies and defense mechanisms in flowering plants has long been recognized, with trade-offs between investment in defense and reproduction predicted. Glandular trichomes and secretory cavities or ducts, which are epidermal and internal structures, play a pivotal role in the secretion, accumulation, and transport of specialized secondary metabolites, and contribute significantly to defense and pollination. Recent investigations have revealed an intricate connection between these two structures, whereby specialized volatile and non-volatile metabolites are exchanged, collectively shaping their respective ecological functions. However, a comprehensive understanding of this profound integration remains largely elusive. In this review, we explore the secretory systems and associated secondary metabolism primarily in Asteraceous species to propose potential shared mechanisms facilitating the directional translocation of these metabolites to diverse destinations. We summarize recent advances in our understanding of the cooperativity between epidermal and internal secretory structures in the biosynthesis, secretion, accumulation, and emission of terpenes, providing specific well-documented examples from pyrethrum (Tanacetum cinerariifolium). Pyrethrum is renowned for its natural pyrethrin insecticides, which accumulate in the flower head, and more recently, for emitting an aphid alarm pheromone. These examples highlight the diverse specializations of secondary metabolism in pyrethrum and raise intriguing questions regarding the regulation of production and translocation of these compounds within and between its various epidermal and internal secretory systems, spanning multiple tissues, to serve distinct ecological purposes. By discussing the cooperative nature of secretory structures in flowering plants, this review sheds light on the intricate mechanisms underlying the ecological roles of terpenes in defense and pollination.

Antiemetic effects of sclareol, possibly through 5-HT3 and D2 receptor interaction pathways: In-vivo and in-silico studies

BACKGROUND

Emesis is a complex physiological phenomenon that serves as a defense against numerous toxins, stressful situations, adverse medication responses, chemotherapy, and movement. Nevertheless, preventing emesis during chemotherapy or other situations is a significant issue for researchers. Hence, the majority view contends that successfully combining therapy is the best course of action. In-vivo analysis offers a more comprehensive grasp of how compounds behave within a complex biological environment, whereas in-silico evaluation refers to the use of computational models to forecast biological interactions.

OBJECTIVES

The objectives of the present study were to evaluate the effects of Sclareol (SCL) on copper sulphate-induced emetic chicks and to investigate the combined effects of these compounds using a conventional co-treatment approach and in-silico study.

METHODS

SCL (5, 10, and 15 mg/kg) administered orally with or without pre-treatment with anti-emetic drugs (Ondansetron (ODN): 24 mg/kg, Domperidone (DOM): 80 mg/kg, Hyoscine butylbromide (HYS): 100 mg/kg, and Promethazine hydrochloride (PRO): 100 mg/kg) to illustrate the effects and the potential involvement with 5HT3, D2, M3/AChM, H1, or NK1 receptors by SCL. Furthermore, an in-silico analysis was conducted to forecast the role of these receptors in the emetic process.

RESULTS

The results suggest that SCL exerted a dose-dependent anti-emetic effect on the chicks. Pretreatment with SCL-10 significantly minimized the number of retches and lengthened the emesis tendency of the experimental animals. SCL-10 significantly increased the anti-emetic effects of ODN and DOM. However, compared to the ODN-treated group, (SCL-10 + ODN) group considerably (p < 0.0001) extended the latency duration (109.40 ± 1.03 s) and significantly (p < 0.01) decreased the number of retches (20.00 ± 0.70), indicating an anti-emetic effect on the test animals. In in-silico analysis, SCL exhibited promising binding affinities with suggesting receptors.

CONCLUSION

SCL-10 exerted an inhibitory-like effect on emetic chicks, probably through the interaction of the 5HT3 and D2 receptors. Further studies are highly appreciated to validate this study and determine the precise mechanism(s) behind the anti-emetic effects of SCL. We expect that SCL-10 may be utilized as an antiemetic treatment in a single dosage form or that it may function as a synergist with other traditional medicines.

Salvia officinalis L. and Salvia sclarea Essential Oils: Chemical Composition, Biological Activities and Preservative Effects against Listeria monocytogenes Inoculated into Minced Beef Meat

In this study, Salvia officinalis L. and Salvia sclarea essential oils (EOs) were investigated using gas chromatography-mass spectrometry (GC-MS) to describe their chemical composition. The obtained results show, for both EOs, a profile rich in terpene metabolites, with monoterpenes predominating sesquiterpenes but with significant qualitative and quantitative differences. The main compound found in the Salvia officinalis EO (SOEO) was camphor (19.0%), while in Salvia sclarea EO (SCEO), it was linalyl acetate (59.3%). Subsequently, the in vitro antimicrobial activity of the EOs against eight pathogenic strains was evaluated. The disc diffusion method showed a significant lysis zone against Gram-positive bacteria. The minimum inhibitory concentrations (MICs) ranged from 3.7 mg/mL to 11.2 mg/mL, indicating that each EO has specific antimicrobial activity. Both EOs also showed significant antiradical activity against DPPH radicals and total antioxidant activity. In addition, the preservative effect of SOEO (9.2%) and SCEO (9.2%), alone or in combination, was tested in ground beef, and the inhibitory effect against Listeria monocytogenes inoculated into the raw ground beef during cold storage was evaluated. Although the effect of each individual EO improved the biochemical, microbiological, and sensory parameters of the samples, their combination was more effective and showed complete inhibition of L. monocytogenes after 7 days of storage at 4 °C. The results show that both EOs could be used as safe and natural preservatives in various food and/or pharmaceutical products.

Novel hybrids of sclareol and 1,2,4-triazolo[1,5-a]pyrimidine show collateral sensitivity in multidrug-resistant glioblastoma cells

The synthesis of 24 hybrid molecules, consisting of naturally occurring sclareol (SCL) and synthetic 1,2,4-triazolo[1,5-a]pyrimidines (TPs), is described. New compounds were designed with the aim of improving the cytotoxic properties, activity, and selectivity of the parent compounds. Six analogs (12a-f) contained 4-benzylpiperazine linkage, while 4-benzyldiamine linkage was present in eighteen derivatives (12g-r and 13a-f). Hybrids 13a-f consist of two TP units. After purification, all hybrids (12a-r and 13a-f), as well as their precursors (9a-e and 11a-c), were tested on human glioblastoma U87 cells. More than half of the tested synthesized molecules, 16 out of 31, caused a significant reduction of U87 cell viability (more than 75% reduction) at 30 µM. The concentration-dependent cytotoxicity of these 16 compounds was also examined on U87 cells, corresponding multidrug-resistant (MDR) U87-TxR cells with increased P-glycoprotein (P-gp) expression and activity, and normal lung fibroblasts MRC-5. Importantly, 12l and 12r were active in the nanomolar range, while seven compounds (11b, 11c, 12i, 12l, 12n, 12q, and 12r) were more selective towards glioblastoma cells than SCL. All compounds except 12r evaded MDR, showing even better cytotoxicity in U87-TxR cells. In particular, 11c, 12a, 12g, 12j, 12k, 12m, 12n, and SCL showed collateral sensitivity. Hybrid compounds 12l, 12q, and 12r decreased P-gp activity to the same extent as a well-known P-gp inhibitor - tariquidar (TQ). Hybrid compound 12l and its precursor 11c affected different cellular processes including the cell cycle, cell death, and mitochondrial membrane potential, and changed the levels of reactive oxygen and nitrogen species (ROS/RNS) in glioblastoma cells. Collateral sensitivity towards MDR glioblastoma cells was caused by the modulation of oxidative stress accompanied by inhibition of mitochondria.

Chemical Profiling and Bioactivity Assessment of Helichrysum italicum (Roth) G. Don. Essential Oil: Exploring Pure Compounds and Synergistic Combinations

Helichrysum italicum (Roth) G. Don., immortelle, is a plant species used in ethnomedicine and the food industry as a spice added to food, beverages, and bakery products. It has been shown to possess various biological activities, such as antioxidant and antibacterial activity, making it useful as a natural preservative. We investigated the phytochemical profile and biological activity of H. italicum essential oils from wild-grown plant material collected from natural habitats in the Republic of Croatia and Bosnia and Herzegovina. Using high-resolution scanning electron microscopy (SEM), a visual investigation of plant organs (stem, leaf, and flower) was performed, confirming the presence of essential oil reservoirs on the surface of all examined plant organs. Essential oils were isolated by hydrodistillation in the Clevenger apparatus. The chemical composition of the essential oils was determined using the GC-MS analytical technique. Cytotoxic activity tests were performed in vitro on three cell lines: skin (fibroblast), lung, and breast cancer. Using statistical tools, the synergistic and selective effects of H. italicum essential oil on healthy and tumor cells were correlated to chemical composition and cytotoxic activity. The synergistic and antagonistic effects of H. italicum essential oil's individual components were simulated by testing pure compounds and their mixture of cytotoxic activity on fibroblasts and breast cancer cells. The results confirm that essential oil's biological activity is much greater than the sum of the effects of its components. The present data are novel contributions to the body of knowledge on the biological activity of this species used in the food industry.

Supercritical Fluid Extraction of Essential Oil and Sclareol from a Clary Sage Concrete

Clary Sage extracts are of industrial interest: in particular, sclareol shows a strong pharmaceutical potential. Supercritical fluid extraction was used to recover compounds of interest from a Salvia sclarea L. waxy n-hexane extract ("concrete"), using semi-continuous fractionation and a multi-step extraction strategy. Multi-step extraction experiments were carried out in two phases: the first one operated at 90 bar and 50 °C; the second one at 100 bar and 40 °C. GC-MS traces showed that during the first extraction step, only lighter compounds (e.g., monoterpenes, sesquiterpenes, and derivatives) were collected, whereas, in the second step, only sclareol and related compounds were recovered. By adjusting operating conditions (temperature and pressure), selective extraction of different families of compounds was accomplished, with no further need for post-processing of the products. Moreover, using two separators in series, the compounds of interest were fractionated from paraffins and, by changing the operating conditions, the extraction yield increased from about 6.0% to 9.3% w/w as CO₂ density increased.

Chemical Composition and Biological Activity of Salvia officinalis L. Essential Oil

In our study, we investigated the chemical composition and cytotoxic activity of essential oils isolated from Dalmatian sage (Salvia officinalis L.) collected along the Adriatic coast of Croatia. Scanning electron microscopy (SEM) was used to examine the morphology of the stem and leaf surfaces. Essential oil excretory glands were detected on both the leaves and stem surfaces. The essential oils were isolated by hydrodistillation, and their chemical composition was determined by gas chromatography and mass spectrometry (GC-MS). Sage essential oils were mixtures of terpene compounds, among which the most common were: α- and β-thujone, camphor, and 1,8-cineol. Cytotoxic activity was tested using MTS assay on multiple cell lines: normal and immortalized fibroblasts (HF77FA and HDF-Tert), immortalized lung line (BEAS-2B), and breast adenocarcinoma (MDA-MB-231). The growth of treated cells was determined relative to control conditions without treatment. The immortalized lung line was the least resistant to the activity of the essential oils, whereas immortalized fibroblasts were the most resistant. Statistical analysis has connected the cytotoxic effect and chemical composition of the studied essential oils. To the best of our knowledge, this work is the first testing of the cytotoxic activity of S. officinalis EO's on the BEAS-2B, HF77FA, and HDF-Tert cell lines. The presented data on essential oil chemical composition and cytotoxic effect on 4 types of human cells supports pharmacotherapeutic potential this plant is known to have.

Phytochemical Profile of Foeniculum vulgare Subsp. piperitum Essential Oils and Evaluation of Acaricidal Efficacy against Varroa destructor in Apis mellifera by In Vitro and Semi-Field Fumigation Tests

Varroatosis is an important parasitic disease of Apis mellifera caused by the mite Varroa destructor (V. destructor). The parasite is able to transmit numerous pathogens to honeybees which can lead to colony collapse. In recent years, the effectiveness of authorized drug products has decreased due to increasing resistance phenomena. Therefore, the search for alternatives to commercially available drugs is mandatory. In this context, essential oils (EOs) prove to be a promising choice to be studied for their known acaricide properties. In this research work, the acaricide activity of EO vapours isolated from the epigeal part (whole plant) of fennel (Foeniculum vulgare sbps. piperitum) and its three fractions (leaves, achenes and flowers) against V. destructor was evaluated. The effectiveness of fumigation was studied using two methods. The first involved prolonged exposure of mites to oil vapour for variable times. After exposure, the five mites in each replicate were placed in a Petri dish with an Apis mellifera larva. Mortality, due to chronic toxicity phenomena, was assessed after 48 h. The second method aimed to translate the results obtained from the in vitro test into a semi-field experiment. Therefore, two-level cages were set up. In the lower compartment of the cage, a material releasing oil vapours was placed; in the upper compartment, Varroa-infested honeybees were set. The results of the first method showed that the increase in mortality was directly proportional to exposure time and concentration. The whole plant returned 68% mortality at the highest concentration (2 mg/mL) and highest exposure time (48 h control), while the leaves, achenes and flowers returned 64%, 52% and 56% mortality, respectively. In the semi-field experiment, a concentration up to 20 times higher than the one used in the in vitro study was required for the whole plant to achieve a similar mite drop of >50%. The results of the study show that in vitro tests should only be used for preliminary screening of EO activity. In vitro tests should be followed by semi-field tests, which are essential to identify the threshold of toxicity to bees and the effective dose to be used in field studies.

The bioactivities of sclareol: A mini review

Sclareol, a diterpene alcohol isolated from the herbal and flavor plant clary sage (Salvia sclarea L.), is far-famed as the predominant ingredient in the refined oil of Salvia sclarea (L.). The empirical medicine of Salvia sclarea L. focused on various diseases, such as arthritis, oral inflammation, digestive system diseases, whereas the sclareol possessed more extensive and characteristic bioactivities, including anti-tumor, anti-inflammation and anti-pathogenic microbes, even anti-diabetes and hypertension. However, there is a deficiency of literature to integrate and illuminate the pharmacological attributes of sclareol based on well-documented investigations. Interestingly, sclareol has been recently considered as the potential candidate against COVID-19 and Parkinson’s disease. Accordingly, the bioactive attributes of sclareol in cancer, inflammation, even pharmacochemistry and delivery systems are reviewed for comprehensively dissecting its potential application in medicine.

Terpenoids and their gene regulatory networks in Opisthopappus taihangensis 'Taihang Mingzhu' as detected by transcriptome and metabolome analyses

'Taihang Mingzhu' is the hybrid offspring of Opisthopappus taihangensis, and it has an excellent characteristic of whole-plant fragrance. At present, the genes and metabolites involved in the synthesis of its aromatic compounds are unknown because of the paucity of molecular biology studies on flowering in the Opisthopappus Shih genus. To elucidate the biosynthetic pathways of terpenoids, the main aromatic compounds in 'Taihang Mingzhu', we conducted transcriptome and metabolite analyses on its leaves and bud, inflorescences at the color-development, flowering, and full-bloom stages. A total of 82,685 unigenes were obtained, of which 43,901 were annotated on the basis of information at the protein databases Nr, SwissProt, KEGG, and COG/KOG (e-value<0.00001). Using gas headspace solid-phase microextraction chromatography - mass spectrometry (HS-SPME-GC/MS), 1350 metabolites were identified, the most abundant of which were terpenoids (302 metabolites). Analyses of the gene regulatory network of terpenoids in 'Taihang Mingzhu' identified 52 genes potentially involved in the regulation of terpenoid synthesis. The correlations between genes related to terpenoid metabolism/regulation and metabolite abundance were analyzed. We also extracted the essential oil from the leaves of 'Taihang Mingzhu' by hydrodistillation, and obtained 270 aromatic compounds. Again, the most abundant class was terpenoids. These results provide guidance for the extraction of essential oil from 'Taihang Mingzhu' leaves and flowers. In addition, our analyses provide valuable genetic resources to identify genetic targets to manipulate the aromatic profiles of this plant and other members the Opisthopappus Shih genus by molecular breeding.

Sclareol and linalyl acetate are produced by glandular trichomes through the MEP pathway

Sclareol, an antifungal specialized metabolite produced by clary sage, Salvia sclarea, is the starting plant natural molecule used for the hemisynthesis of the perfume ingredient ambroxide. Sclareol is mainly produced in clary sage flower calyces; however, the cellular localization of the sclareol biosynthesis remains unknown. To elucidate the site of sclareol biosynthesis, we analyzed its spatial distribution in the clary sage calyx epidermis using laser desorption/ionization mass spectrometry imaging (LDI-FTICR-MSI) and investigated the expression profile of sclareol biosynthesis genes in isolated glandular trichomes (GTs). We showed that sclareol specifically accumulates in GTs' gland cells in which sclareol biosynthesis genes are strongly expressed. We next isolated a glabrous beardless mutant and demonstrate that more than 90% of the sclareol is produced by the large capitate GTs. Feeding experiments, using 1-¹³C-glucose, and specific enzyme inhibitors further revealed that the methylerythritol-phosphate (MEP) biosynthetic pathway is the main source of isopentenyl diphosphate (IPP) precursor used for the biosynthesis of sclareol. Our findings demonstrate that sclareol is an MEP-derived diterpene produced by large capitate GTs in clary sage emphasing the role of GTs as biofactories dedicated to the production of specialized metabolites.

Study of the genetic and phenotypic variation among wild and cultivated clary sages provides interesting avenues for breeding programs of a perfume, medicinal and aromatic plant

A road-map of the genetic and phenotypic diversities in both crops and their wild related species can help identifying valuable genetic resources for further crop breeding. The clary sage (Salvia sclarea L.), a perfume, medicinal and aromatic plant, is used for sclareol production and ornamental purposes. Despite its wide use in the field of cosmetics, the phenotypic and genetic diversity of wild and cultivated clary sages remains to be explored. We characterized the genetic and phenotypic variation of a collection of six wild S. sclarea populations from Croatia, sampled along an altitudinal gradient, and, of populations of three S. sclarea cultivars. We showed low level of genetic diversity for the two S. sclarea traditional cultivars used for essential oil production and for ornamental purposes, respectively. In contrast, a recent cultivar resulting from new breeding methods, which involve hybridizations among several genotypes rather than traditional recurrent selection and self-crosses over time, showed high genetic diversity. We also observed a marked phenotypic differentiation for the ornamental clary sage compared with other cultivated and wild clary sages. Instead, the two cultivars used for essential oil production, a traditional and a recent one, respectively, were not phenotypically differentiated from the wild Croatian populations. Our results also featured some wild populations with high sclareol content and early-flowering phenotypes as good candidates for future breeding programs. This study opens up perspectives for basic research aiming at understanding the impact of breeding methods on clary sage evolution, and highlights interesting avenues for clary breeding programs.

Essential Oil Profile and Yield of Corolla, Calyx, Leaf, and Whole Flowering Top of Cultivated Lavandula angustifolia Mill. (Lamiaceae) from Utah

Lavandula angustifolia Mill. (lavender) is an essential-oil-bearing plant in the Lamiaceae family. Volatile oil produced through the steam distillation of lavender was examined to establish the essential oil yield and aromatic profile from each portion of the plant-namely, the corolla, calyx, leaf, and whole flowering top. The resulting essential oils were analyzed by GC-FID and GC-MS. The different plant parts generally shared similar compounds but in varying relative percentages. Aromatic profiles of the whole flowering top and calyx were similar, with prominent compounds being linalool acetate (34.3%, 32.0%), linalool (26.5%, 32.9%), lavandulyl acetate (5.6%, 4.9%), terpinen-4-ol (5.3%, 7.0%), and (Z)-β-ocimene (4.5%, 5.4%), respectively. Aromatic profiles for the corolla and leaf were unique. Prominent aromatic compounds of the corolla included linalool acetate (18.4%), linalool (10.8%), epi-α-cadinol (10.0%), borneol (7.3%), and lavandulyl acetate (6.3%). Prominent aromatic compounds of the leaf included epi-α-cadinol (19.8%), γ-cadinene (11.0%), borneol (6.0%), caryophyllene oxide (4.9%), and bornyl acetate (4.8%). Complete profiles and essential oil yields of corolla, calyx, leaf, and whole flowering top were established. This study establishes the influence the corolla, calyx, and leaf exert on the aromatic profile of the whole flowering top and provides insight into authentication of lavender essential oil.

Essential Oil Composition and Micromorphological Traits of Satureja montana L., S. subspicata Bartel ex Vis., and S. kitaibelii Wierzb. Ex Heuff. Plant Organs

The essential oil (EO) composition of Satureja plants is highly variable. Recent studies suggest that there is an even difference in the EO composition from different plant organs within the same plant. This study aims to examine the chemical profile of EOs and the micromorphological characteristics of different organs of three Satureja species. The relationship between the number of glandular trichomes and EOs profile and relative yield is also investigated. Individuals from five populations were visualized using a scanning electron microscope, while EOs of leaves, calyces, corollas, and whole aerial parts were isolated using simultaneous distillation and extraction and analyzed using gas chromatography/mass spectrometry. Three types of glandular trichomes were detected. Peltate trichomes were present on all plant organs of studied species, while two types of capitate trichomes show different organ and species preferences. The EOs profiles differed across the plant parts, but showed a species specific composition. Univariate and multivariate statistics were used to show a correlation between the peltate trichomes and EO yield, and chemophenetic significance of EO profiles.

Improved cis-Abienol production through increasing precursor supply in Escherichia coli

cis-Abienol, a natural diterpene-diol isolated from balsam fir (Abies balsamea), can be employed as precursors for the semi-synthesis of amber compounds, which are sustainable replacement for ambergris and widely used in the fragmented industry. This study combinatorially co-expressed geranyl diphosphate synthase, geranylgeranyl diphosphate synthase, Labda-13-en-8-ol diphosphate synthase and diterpene synthase, with the best combination achieving ~ 0.3 mg/L of cis-abienol. An additional enhancement of cis-abienol production (up to 8.6 mg/L) was achieved by introducing an exogenous mevalonate pathway which was divided into the upper pathway containing acetyl-CoA acetyltransferase/HMG-CoA reductase and HMG-CoA synthase and the lower pathway containing mevalonate kinase, phosphomevalonate kinase, pyrophosphate mevalonate decarboxylase and isopentenyl pyrophosphate isomerase. The genetically modified strain carrying chromosomal copy of low genes of the mevalonate with the trc promoter accumulated cis-abienol up to 9.2 mg/L in shake flask. Finally, cis-abienol titers of ~ 220 mg/L could be achieved directly from glucose using this de novo cis-abienol-producing E. coli in high-cell-density fermentation. This study demonstrates a microbial process to apply the E. coli cell factory in the biosynthesis of cis-abienol.

Effect of natural boron mineral use on the essential oil ratio and components of Musk Sage (Salvia sclarea L.)

This study was aimed to determine the effect of different boron doses (boron free, pure boron with 8 liters per decare and in 1/8 ratio diluted boron) on the rate and quality of volatile oil in musk grown in Kütahya-Gediz conditions. Essential oil from Musk Sage was obtained by hydrodistillation method (GC-MS/FID). In the analysis carried out in 2017, the rate of essential oil was found to be 0.11% in the plant grown without boron, while it was 0.44% in the plant grown with pure boron. However, this rate was found as 0.23% in the 1/8 boron ratio application. The main components of volatile oil were found as follows: for the boron-free application—spathulenol 23.75%, caryophyllene oxide 19.41%, linalool 10.10%, and sclareoloxide 9.92%; for the pure dose application—spathulenol 26.67%, sclareoloxide 18.81%, and caryophyllene oxide 16.13%; for in 1/8 ratio diluted boron dose application—spathulenol 24.82%, sclareoloxide 16.68%, and caryophyllene oxide 14.86%. It has been observed that pure boron dose has a positive effect on the essential oil ratio and components of Musk Sage.

Morphological characterization of domatium development in Callicarpa saccata

BACKGROUND AND AIMS

Domatia are plant structures within which organisms reside. Callicarpa saccata (Lamiaceae) is the sole myrmecophyte, or 'ant plant', that develops foliar (leaf-borne) myrmeco-domatia in this genus. In this work we examined domatium development in C. saccata to understand the developmental processes behind pouch-like domatia.

METHODS

Scanning electron microscopy, sectioning and microcomputed tomography were carried out to compare the leaves of C. saccata with those of the closely related but domatia-less myrmecophyte Callicarpa subaequalis, both under cultivation without ants.

KEY RESULTS

Callicarpa saccata domatia are formed as a result of excess cell proliferation at the blade/petiole junctions of leaf primordia. Blade/petiole junctions are important meristematic sites in simple leaf organogenesis. We also found that the mesophyll tissue of domatia does not clearly differentiate into palisade and spongy layers.

CONCLUSIONS

Rather than curling of the leaf margins, a perturbation of the normal functioning of the blade/petiole junction results in the formation of domatium tissue. Excess cell proliferation warps the shape of the blade and disturbs the development of the proximal-distal axis. This process leads to the generation of distinct structures that facilitate interaction between C. saccata and ants.

Non-volatile natural products in plant glandular trichomes: chemistry, biological activities and biosynthesis

The investigation methods, chemistry, bioactivities, and biosynthesis of non-volatile natural products involving 489 compounds in plant glandular trichomes are reviewed.

Differential metabolic specialization of foliar oil glands in Eucalyptus brevistylis Brooker (Myrtaceae)

Trees and shrubs from the genus Eucalyptus are characterized by the presence of numerous foliar oil glands that generally house mono- and sesquiterpenes. In some species, glands are also known to house substantial quantities of unrelated secondary metabolites such as volatile, aromatic β-triketones. It is not known if these compounds are co-housed with terpenes or if they are produced in distinct, metabolically specialized glands. We showed that Eucalyptus brevistylis-a species with appreciable foliar quantities of both β-triketones and terpenes-contains two visually distinct gland types in leaves, one that is translucent and the other golden-brown. Gas chromatographic analyses of solvent extracts of the two gland types showed that the translucent glands contain sesquiterpene alcohol cubenols and cubebols (termed 'sesquiterpene glands'), whereas the golden-brown glands contain predominantly the β-triketone conglomerone with lesser amounts of sesquiterpene hydrocarbon caryophyllenes (termed 'triketone glands'). Analysis of leaves from trees of different ages, from young saplings through to advanced age trees, showed a gradual increase in the abundance of sesquiterpene glands relative to triketone glands as plants aged. Such ontogenetic regulation of foliar secondary metabolite concentration appears to be a common feature of Eucalyptus species, albeit at different temporal scales. A similar ontogenetic pattern was observed in ageing leaves, with mature leaves having a higher proportion of sesquiterpene glands than young leaf tips. It is concluded that regulation of the relative abundances of the two gland types with ontogeny likely reflects the different herbivores present at the different life stages of leaves and whole plants. In particular, leaf tips and young plants may be advantaged by deploying higher amounts of insecticidal β-triketones. The concurrent deployment of two metabolically distinct gland types in leaves is a rare phenomenon and a novel finding for myrtaceous trees.

Phytochemical Compositions and Antidiabetic Potentials of Salvia sclarea L. Essential Oils

Salvia sclarea (SS) is characterized by its valuable essential oils (Eos) and potent biological activities. This study aimed at investigating the phytochemical composition of SS Eos collected in within the same week, from two different regions in Lebanon, Beirut (SS-Bt) and Taanayel (SS-Tl), utilizing GC-MS methods, and to explore their acute and subchronic antidiabetic potentials. Moreover, studying the phytochemical diversity of twenty SS Eos established on our work and literature descriptions in order to recognize the origin of the Lebanese active chemotype(s). The Eos have been obtained by hydro-distillation and identified via GC-MS analyses. Five chemotypes of SS Eos have been identified. The Lebanese Eos, SS-Bt and SS-Tl, studied here have shown evidence to belong to two different chemotypes 1 and 5, respectively. SS-Bt has shown to belong to chemotype 1, which is characterized by high linalool (LL) concentration (average 40.2%). On the other hand, SS-Tl has shown to belong to chemotype 5, which is characterized by high linalyl acetate (LA) concentration (average 50.4%). The acute and subchronic antidiabetic activities of these EOs have been monitored along with LL and LA, in order to find the most active chemotype. Chemotypes 1 (owned to high LL content), present at low altitude places of Lebanon and Poland, has shown significantly higher acute and subchronic antidiabetic activities than that of chemotype 5 (owned to high LA content). In conclusion, Salvia sclarea Eos have shown potential antidiabetic activities, and their Eos might be used in the future as a complementary or an alternative medicine in the management of diabetes and related complications.

Overexpression of SmMYB9b enhances tanshinone concentration in Salvia miltiorrhiza hairy roots

A Salvia miltiorrhiza R2R3-MYB gene, SmMYB9b , has been cloned and characterized. Overexpression of SmMYB9b resulted in a significant improvement of tanshinones, the lipophilic active ingredients in danshen hairy roots. Plant R2R3-MYB transcription factors play important roles in various physiological and biochemical processes. Danshen (Salvia miltiorrhiza bunge) is a valuable medicinal herb with tanshinones and salvianolic acids as the principal bioactive ingredients. A number of putative R2R3-MYB transcription factors have been identified in the plant, but their function remains to be studied. Here, we report the cloning of SmMYB9b, an S20 R2R3-MYB member and its regulatory properties. SmMYB9b contains an open reading frame of 792 bp in length and encodes a 264-amino acid protein. Its transcripts were most abundant in blooming flowers (except for calyces) and increased with flower development. Exogenous abscisic acid strongly activated its transcription. Gibberellins and methyl jasmonate also showed a time-dependent activation effect on its transcription, but to a weaker degree. Overexpression of SmMYB9b in danshen hairy roots enhanced tanshinone concentration to 2.16 ± 0.39 mg/g DW, a 2.2-fold improvement over the control. In addition to increased tanshinone concentration, the hairy root growth and lateral hairy root formation were also suppressed. KEGG pathway enrichment analysis with de novo RNAseq data indicated that stress-response-related metabolic pathways, such as the terpenoid and plant hormone signal transduction pathways, were significantly enriched, implying possible implication of SmMYB9b in such processes. Quantitative RT-PCR analysis showed that the transcription of terpenoid biosynthetic genes SmDXS2, SmDXR, SmGGPPS, and SmKSL1 was significantly up-regulated in danshen hairy roots over expressing SmMYB9b. These data suggest that overexpression of SmMYB9b results in enhanced tanshinone concentration through stimulation of the MEP pathway. The present findings shed new light on elucidating the roles of R2R3-MYB in the biosynthesis of diterpenoids in S. miltiorrhiza.

A diterpene synthase from the clary sage Salvia sclarea catalyzes the cyclization of geranylgeranyl diphosphate to (8R)-hydroxy-copalyl diphosphate

The bicyclic diterpene (-)-sclareol is accumulated in glandular trichomes in Salvia sclarea (Schmiderer et al., 2008), and is a major terpenoid component of this plant species. It is used as the starting material for Ambrox synthesis, a synthetic ambergris analog used in the flavor and fragrance industry. In order to investigate the formation of sclareol, cDNA prepared from secretory cells of glandular trichomes from S. sclarea inflorescence were randomly sequenced. A putative copalyl diphosphate synthase encoding EST, SscTPS1, was functionally expressed in Escherichia coli. Whereas reaction of geranylgeranyl diphosphate with the putative copalyl diphosphate synthase followed by hydrolysis with alkaline phosphatase yielded a diastereomeric mixture of (13R)- and (13S)-manoyl oxide, HCl hydrolysis yielded (-)-sclareol (1) and 13-epi-sclareol as products. The product of the reaction of SscTPS1 with geranylgeranyl diphosphate was subjected to analysis by LC-negative ion ESI-MS/MS without prior hydrolysis. EPI scans were consistent with copalyl diphosphate to which 18 mass units had added (m/z 467 [M+H](-)). The enzymatic reaction was also carried out in the presence of 60% H2(18)O. LC-negative ion ESI-MS/MS analysis established an additional reaction product consistent with the incorporation of (18)O. Incubation in the presence of 60% (2)H2O resulted in the incorporation of one deuterium atom. These results suggest water capture of the carbocation intermediate, which is known to occur in reactions catalyzed by monoterpene synthases, but has been described only several times for diterpene synthases.

Diversification, biogeographic pattern, and demographic history of Taiwanese Scutellaria species inferred from nuclear and chloroplast DNA

The ragged topography created by orogenesis generates diversified habitats for plants in Taiwan. In addition to colonization from nearby mainland China, high species diversity and endemism of plants is also present in Taiwan. Five of the seven Scutellaria species (Lamiaceae) in Taiwan, for example, are endemic to the island. Hypotheses of multiple sources or in situ radiation have arisen to explain the high endemism of Taiwanese species. In this study, phylogenetic analyses using both nuclear and chloroplast markers revealed the multiple sources of Taiwanese Scutellaria species and confirmed the rapid and recent speciation of endemic species, especially those of the "indica group" composed of S. indica, S. austrotaiwanensis, S. tashiroi, and S. playfairii. The common ancestors of the indica group colonized first in northern Taiwan and dispersed regionally southward and eastward. Climate changes during glacial/interglacial cycles led to gradual colonization and variance events in the ancestors of these species, resulting in the present distribution and genetic differentiation of extant populations. Population decline was also detected in S. indica, which might reflect a bottleneck effect from the glacials. In contrast, the recently speciated endemic members of the indica group have not had enough time to accumulate much genetic variation and are thus genetically insensitive to demographic fluctuations, but the extant lineages were spatially expanded in the coalescent process. This study integrated phylogenetic and population genetic analyses to illustrate the evolutionary history of Taiwanese Scutellaria of high endemism and may be indicative of the diversification mechanism of plants on continental islands.

Extracellular localization of the diterpene sclareol in clary sage (Salvia sclarea L., Lamiaceae)

Sclareol is a high-value natural product obtained by solid/liquid extraction of clary sage (Salvia sclarea L.) inflorescences. Because processes of excretion and accumulation of this labdane diterpene are unknown, the aim of this work was to gain knowledge on its sites of accumulation in planta. Samples were collected in natura or during different steps of the industrial process of extraction (steam distillation and solid/liquid extraction). Samples were then analysed with a combination of complementary analytical techniques (gas chromatography coupled to a mass spectrometer, polarized light microscopy, environmental scanning electron microscopy, two-photon fluorescence microscopy, second harmonic generation microscopy). According to the literature, it is hypothesized that sclareol is localized in oil pockets of secretory trichomes. This study demonstrates that this is not the case and that sclareol accumulates in a crystalline epicuticular form, mostly on calyces.

Discovery and functional characterization of two diterpene synthases for sclareol biosynthesis in Salvia sclarea (L.) and their relevance for perfume manufacture

BACKGROUND

Sclareol is a diterpene natural product of high value for the fragrance industry. Its labdane carbon skeleton and its two hydroxyl groups also make it a valued starting material for semisynthesis of numerous commercial substances, including production of Ambrox® and related ambergris substitutes used in the formulation of high end perfumes. Most of the commercially-produced sclareol is derived from cultivated clary sage (Salvia sclarea) and extraction of the plant material. In clary sage, sclareol mainly accumulates in essential oil-producing trichomes that densely cover flower calices. Manool also is a minor diterpene of this species and the main diterpene of related Salvia species.

RESULTS

Based on previous general knowledge of diterpene biosynthesis in angiosperms, and based on mining of our recently published transcriptome database obtained by deep 454-sequencing of cDNA from clary sage calices, we cloned and functionally characterized two new diterpene synthase (diTPS) enzymes for the complete biosynthesis of sclareol in clary sage. A class II diTPS (SsLPPS) produced labda-13-en-8-ol diphosphate as major product from geranylgeranyl diphosphate (GGPP) with some minor quantities of its non-hydroxylated analogue, (9 S, 10 S)-copalyl diphosphate. A class I diTPS (SsSS) then transformed these intermediates into sclareol and manool, respectively. The production of sclareol was reconstructed in vitro by combining the two recombinant diTPS enzymes with the GGPP starting substrate and in vivo by co-expression of the two proteins in yeast (Saccharomyces cerevisiae). Tobacco-based transient expression assays of green fluorescent protein-fusion constructs revealed that both enzymes possess an N-terminal signal sequence that actively targets SsLPPS and SsSS to the chloroplast, a major site of GGPP and diterpene production in plants.

CONCLUSIONS

SsLPPS and SsSS are two monofunctional diTPSs which, together, produce the diterpenoid specialized metabolite sclareol in a two-step process. They represent two of the first characterized hydroxylating diTPSs in angiosperms and generate the dihydroxylated labdane sclareol without requirement for additional enzymatic oxidation by activities such as cytochrome P450 monoxygenases. Yeast-based production of sclareol by co-expresssion of SsLPPS and SsSS was efficient enough to warrant the development and use of such technology for the biotechnological production of scareol and other oxygenated diterpenes.

Seasonal influence on gene expression of monoterpene synthases in Salvia officinalis (Lamiaceae)

Garden sage (Salvia officinalis L., Lamiaceae) is one of the most important medicinal and aromatic plants and possesses antioxidant, antimicrobial, spasmolytic, astringent, antihidrotic and specific sensorial properties. The essential oil of the plant, formed mainly in very young leaves, is in part responsible for these activities. It is mainly composed of the monoterpenes 1,8-cineole, α- and β-thujone and camphor synthesized by the 1,8-cineole synthase, the (+)-sabinene synthase and the (+)-bornyl diphosphate synthase, respectively, and is produced and stored in epidermal glands. In this study, the seasonal influence on the formation of the main monoterpenes in young, still expanding leaves of field-grown sage plants was studied in two cultivars at the level of mRNA expression, analyzed by qRT-PCR, and at the level of end-products, analyzed by gas chromatography. All monoterpene synthases and monoterpenes were significantly influenced by cultivar and season. 1,8-Cineole synthase and its end product 1,8-cineole remained constant until August and then decreased slightly. The thujones increased steadily during the vegetative period. The transcript level of their corresponding terpene synthase, however, showed its maximum in the middle of the vegetative period and declined afterwards. Camphor remained constant until August and then declined, exactly correlated with the mRNA level of the corresponding terpene synthase. In summary, terpene synthase mRNA expression and respective end product levels were concordant in the case of 1,8-cineole (r=0.51 and 0.67 for the two cultivars, respectively; p<0.05) and camphor (r=0.75 and 0.82; p<0.05) indicating basically transcriptional control, but discordant for α-/β-thujone (r=-0.05 and 0.42; p=0.87 and 0.13, respectively).

Amphilectane diterpenes from Salvia sclarea: biosynthetic considerations

Salviatrienes A and B, two new diterpenes belonging to the amphilectane/elisabethane family, have been isolated from an extract of clary sage (Salvia sclarea). These molecules are the first representatives of this family to be described from the plant kingdom. This study has led to consideration of the possible enzymatic machinery and biosynthesis pathways within S. sclarea.

The isogene 1-deoxy-D-xylulose 5-phosphate synthase 2 controls isoprenoid profiles, precursor pathway allocation, and density of tomato trichomes

Plant isoprenoids are formed from precursors synthesized by the mevalonate (MVA) pathway in the cytosol or by the methyl-D-erythritol 4-phosphate (MEP) pathway in plastids. Although some exchange of precursors occurs, cytosolic sesquiterpenes are assumed to derive mainly from MVA, while plastidial monoterpenes are produced preferentially from MEP precursors. Additional complexity arises in the first step of the MEP pathway, which is typically catalyzed by two divergent 1-deoxy-D-xylulose 5-phosphate synthase isoforms (DXS1, DXS2). In tomato (Solanum lycopersicum), the SlDXS1 gene is ubiquitously expressed with highest levels during fruit ripening, whereas SlDXS2 transcripts are abundant in only few tissues, including young leaves, petals, and isolated trichomes. Specific down-regulation of SlDXS2 expression was performed by RNA interference in transgenic plants to investigate feedback mechanisms. SlDXS2 down-regulation led to a decrease in the monoterpene β-phellandrene and an increase in two sesquiterpenes in trichomes. Moreover, incorporation of MVA-derived precursors into residual monoterpenes and into sesquiterpenes was elevated as determined by comparison of ¹³C to ¹²C natural isotope ratios. A compensatory up-regulation of SlDXS1 was not observed. Down-regulated lines also exhibited increased trichome density and showed less damage by leaf-feeding Spodoptera littoralis caterpillars. The results reveal novel, non-redundant roles of DXS2 in modulating isoprenoid metabolism and a pronounced plasticity in isoprenoid precursor allocation.

Differential accumulation of volatile terpene and terpene synthase mRNAs during lavender (Lavandula angustifolia and L. x intermedia) inflorescence development

Despite the commercial importance of Lavandula angustifolia Mill. and L. x intermedia Emeric ex Loisel floral essential oils (EOs), no information is currently available on potential changes in individual volatile organic compound (VOC) content during inflorescence development. Calyces were found to be the main sites of VOC accumulation. The 20 most abundant VOCs could be separated into three sub-groups according to their patterns of change in concentration The three groups of VOCs sequentially dominated the global scent bouquet of inflorescences, the transition between the first and second groups occurring around the opening of the first flower of the inflorescence and the one between the second and third groups at the start of seed set. Changes in calyx VOC accumulation were linked to the developmental stage of individual flowers. Leaves accumulated a smaller number of VOCs which were a subset of those seen in preflowering inflorescences. Their nature and content remained constant during the growing season. Quantitative real time polymerase chain reaction assessments of the expression of two terpene synthase (TPS) genes, LaLIMS and LaLINS, revealed similar trends between their patterns of expression and those of their VOC products. Molecular and chemical analyses suggest that changes in TPS expression occur during lavender inflorescence development and lead to changes in EO composition. Both molecular data and terpene analysis support the findings that changes in biosynthesis of terpene occurred during inflorescence development.

Essential Oils and Anxiolytic Aromatherapy

A number of essential oils are currently in use as aromatherapy agents to relieve anxiety, stress, and depression. Popular anxiolytic oils include lavender (Lavandula angustifolia), rose (Rosa damascena), orange (Citrus sinensis), bergamot (Citrus aurantium), lemon (Citrus limon), sandalwood (Santalum album), clary sage (Salvia sclarea), Roman chamomile (Anthemis nobilis), and rose-scented geranium (Pelargonium spp.). This review discusses the chemical constituents and CNS effects of these aromatherapeutic essential oils, as well as recent studies on additional essential oils with anxiolytic activities.

Diversity of Essential Oil Glands of Spanish Sage (Salvia Lavandulifolia Vahl, Lamiaceae)

Salvia lavandulifolia (Spanish sage, Lamiaceae) is widely cultivated in the Mediterranean region and used for the flavor and food industry, perfumery and medicinal purposes. The essential oil, which is responsible for the specific flavor, is produced and stored in specialized epidermal oil glands. In S. lavandulifolia peltate essential oil glands occur on all aerial parts of the plant. The content of single oil glands from different positions on the plant (leaf, calyx, corolla and anther) were directly sampled using a solid-phase micro-extraction (SPME) fiber and analyzed by GC/FID and GC/MS in order to study the variability of the essential oil composition. It was found that the composition of terpenoids is quite variable within a plant. The leaves and calyces are characterized by the main compounds, 1,8-cineole, camphor and β-pinene, and by the sesquiterpenes α-humulene and β-caryophyllene. The corolla shows the highest proportion of borneol, but a low concentration of camphor. In the essential oil of the anthers the percentages of limonene, β-pinene and the diterpene manool are by far higher than in all other plant parts, whereas the proportions of camphor and the sesquiterpenes are considerably lower.