Peltate Glandular Trichomes Research Articles

Volatile compositions and glandular trichomes of Zataria multiflora in different phenological stages under normal and drought stress conditions

BackgroundZataria multiflora Boiss. is a medicinal and aromatic plant from the Lamiaceae family. It is extensively used in Iranian traditional medicine, mostly as a replacement for Thyme species. This study was focused on the analysis of chemical composition and the distribution and types of trichomes of Z. multiflora grown under different conditions. Equilibrium headspace analysis in combination with GC-FID-MS was used to identify volatile compounds released by aerial parts of Z. multiflora in development stages of 50 and 100% flowering under normal and drought-stress conditions.ResultsThe main constituents were p-cymene (20.06–27.40%), γ-terpinene (12.44–16.93%), and α-pinene (6.91–16.58%) and thymol (8.52–9.99%). The highest content of p-cymene (27.40%) and thymol (9.99%) was observed in the 50% flowering stage at the 90% field capacity, while the maximum γ-terpinene (16.93%) content was recorded in the 100% flowering stage under normal conditions. Using the SEM method, it was found that peltate glandular and non-glandular trichomes are distributed on the surface of the leaf, stem, and outer side of the calyx. However, capitate trichomes only are detected on the stem and calyx in the 100% flowering and beginning of blooming stages, respectively. The type and structure of trichomes do not vary in different development stages, but they differ in density. The highest number of leaf peltate glandular trichomes was observed in the vegetative and beginning of blooming stages at 50% and 90% field capacity, respectively. Non-glandular trichomes of the stem were observed with high density in both normal and stress conditions, which are more densely in 90% field capacity.ConclusionsSince this plant has strong potential to be used in the food and pharmacological industries, this study provides valuable information for its cultivation and harvesting at specific phenological stages, depending on desired compounds and their concentrations.

Updating the Knowledge on the Secretory Machinery of Hops (Humulus lupulus L., Cannabaceae).

Cannabaceae species garner attention in plant research due to their diverse secretory structures and pharmacological potential associated with the production of secondary metabolites. This study aims to update our understanding of the secretory system in Hops (Humulus lupulus L.), an economically important species especially known for its usage in beer production. For that, stems, leaves, roots, and inflorescences were collected and processed for external morphology, anatomical, histochemical, ultrastructural and cytochemical analyses of the secretory sites. Our findings reveal three types of secretory structures comprising the secretory machinery of Hops: laticifer, phenolic idioblasts and glandular trichomes. The laticifer system is articulated, anastomosing and unbranched, traversing all plant organs, except the roots. Phenolic idioblasts are widely dispersed throughout the leaves, roots and floral parts of the species. Glandular trichomes appear as two distinct morphological types: capitate (spherical head) and peltate (radial head) and are found mainly in foliar and floral parts. The often-mixed chemical composition in the secretory sites serves to shield the plant from excessive UVB radiation, elevated temperatures, and damage inflicted by herbivorous animals or pathogenic microorganisms. Besides the exudate from peltate glandular trichomes (lupulin glands), latex and idioblast content are also likely contributors to the pharmacological properties of different Hop varieties, given their extensive presence in the plant body.

Unveiling the role of vermicompost in modulating phenylpropanoid metabolism in basil (Ocimum basilicum L.): A single-cell type PGT approach

This research delves into phenylpropanoid metabolism, focusing on phenylpropene biosynthesis in the methyleugenol chemotype of basil (Ocimum basilicum L.). We isolated peltate glandular trichomes (PGTs) from basil leaves to eliminate primary metabolic influences, offering a unique perspective into these complex processes. Vermicompost, chosen for its eco-friendly composition and superiority in invigorating phenylpropanoid metabolism. In this study, we investigated the impacts of solid and tea-form vermicompost applications at 0%, 10%, and 25% doses on the methyleugenol chemotype of basil, focusing on the expression levels of PAL, 4CL, EGS, EOMT, and CVOMT genes and phenylpropene accumulation in the peltate glandular trichomes. Results showed that 10% solid vermicompost (SV) application increased 4CL expression level at 236%, while 25% SV application further enhanced EOMT and CVOMT expressions to towering values by 7,494-fold and 19,643-fold, respectively. SV applications did not significantly impact eugenol accumulation but suppressed chavicol biosynthesis. Methyleugenol and methylchavicol accumulation rose in a dose-dependent manner, with significant increases observed in the 25% SV application. A positive correlation was found between CVOMT expression and accumulation rates of methyleugenol and methylchavicol phenylpropenes following SV applications. Conversely, vermicompost tea (VT) applications led to mixed gene expression patterns and reduced eugenol and methyleugenol ratios in peltate glandular trichomes compared to control. In summary, the notably high gene expressions observed in the results of our preliminary study offer a new perspective in the field of phenylpropanoid metabolism. This underscores the value of utilizing single-cell type PGTs for examining secondary metabolic pathways in plants and demonstrates the impact of vermicompost on phenylpropene production.

Enhancing growth, vitality, and aromatic richness: unveiling the dual magic of silicon dioxide and titanium dioxide nanoparticles in Ocimum tenuiflorum L.

Ocimum tenuiflorum, commonly known as "Holy basil," is renowned for its notable medicinal and aromatic attributes. Its unique fragrance attributes to specific volatile phytochemicals, primarily belonging to terpenoid and/or phenylpropanoid classes, found within their essential oils. The use of nanoparticles (NPs) in agriculture has attracted attention among plant researchers. However, the impact of NPs on the modulation of morpho-physiological aspects and essential oil production in medicinal plants has received limited attention. Consequently, the present study aimed to explore the effect of silicon dioxide (SiO2) and titanium dioxide (TiO2) nanoparticles at various concentrations (viz., DDW (control), Si50+Ti50, Si100+Ti50, Si100+Ti100, Si200+Ti100, Si100+Ti200 and Si200+Ti200 mg L-1) on growth, physiology and essential oil production of O. tenuiflorum at 120 days after planting (DAP). The results demonstrated that the combined application of Si and Ti (Si100+Ti100 mg L-1) exhibited the most favourable outcomes compared to the other combinational treatments. This optimal treatment significantly increased the vegetative growth parameters (root length (33.5%), shoot length (39.2%), fresh weight (62.7%) and dry weight (28.5%)), photosynthetic parameters, enzymatic activities (nitrate reductase and carbonic anhydrase), the overall area of PGTs (peltate glandular trichomes) and essential oil content (172.4%) and yield (323.1%), compared to the control plants. Furthermore, the GCMS analysis showed optimal treatment (Si100+Ti100) significantly improved the content (43.3%) and yield (151.3%) of eugenol, the primary active component of the essential oil. This study uncovers a remarkable and optimal combination of SiO2 and TiO2 nanoparticles that effectively enhances the growth, physiology, and essential oil production in Holy basil. These findings offer valuable insights into maximizing the potential benefits of its use in industrial applications.

A non-canonical Aux/IAA gene MsIAA32 regulates peltate glandular trichome development in spearmint.

Phytohormone auxin controls various aspects of plant growth and development. The typical auxin signalling involves the degradation of canonical Aux/IAA proteins upon auxin perception releasing the auxin response factors (ARF) to activate auxin-regulated gene expression. Extensive research has been pursued in deciphering the role of canonical Aux/IAAs, however, the function of non-canonical Aux/IAA genes remains elusive. Here we identified a non-canonical Aux/IAA gene, MsIAA32 from spearmint (Mentha spicata), which lacks the TIR1-binding domain and shows its involvement in the development of peltate glandular trichomes (PGT), which are the sites for production and storage of commercially important essential oils. Using yeast two-hybrid studies, two canonical Aux/IAAs, MsIAA3, MsIAA4 and an ARF, MsARF3 were identified as the preferred binding partners of MsIAA32. Expression of a R2R3-MYB gene MsMYB36 and a cyclin gene MsCycB2-4 was altered in MsIAA32 suppressed plants indicating that these genes are possible downstream targets of MsIAA32 mediated signalling. Ectopic expression of MsIAA32 in Arabidopsis affected non-glandular trichome formation along with other auxin related developmental traits. Our findings establish the role of non-canonical Aux/IAA mediated auxin signalling in PGT development and reveal species-specific functionalization of Aux/IAAs.

Gallic acid as a phytostimulant enhancing yield and quality of Mentha spicata L. under deficit- and well-watered conditions

Here, we propose gallic acid (GA) as a phytostimulant for Mentha spicata subsp. spicata L. (spearmint), an aromatic herb of great global economic importance. Our evidence would suggest the potential of GA in promoting the acclimation of spearmint to drought stress (DS), also improving yield and quality of its essential oil (EO). We observed that GA and DS did not induce significant morphometric (e.g., stem length) and physiological (e.g., redox state, water content) modifications, indicating an innate tolerance of M. spicata to both these factors. However, spectrophotometric, HPLC-DAD and GC-MS analyses revealed that GA tended to induce the accumulation of some phytochemicals (e.g., terpenoids), mainly responsible for fragrance, quality and bioactivity of EO. Additionally, plants exposed to GA increased the number of peltate glandular trichomes and their content in mono- and sesqui-terpenes. Finally, we demonstrated that DS determined a reduction of spearmint EO yield, while GA significantly favoured it, especially at low doses, both in deficit- and well-watered conditions. Since an increase of GA concentration in roots and/or leaves of the treated plants was not observed, we hypothesised that the proposed phytostimulant exerted its activity indirectly, that is by modulating rhizobiota and/or soil structure and features or triggering signalling transduction pathways starting from the rhizodermis.

Advanced metabolic engineering strategies for increasing artemisinin yield in Artemisia annua L.

Artemisinin, also known as 'Qinghaosu', is a chemically sesquiterpene lactone containing an endoperoxide bridge. Due to the high activity to kill Plasmodium parasites, artemisinin and its derivatives have continuously served as the foundation for antimalarial therapies. Natural artemisinin is unique to the traditional Chinese medicinal plant Artemisia annua L., and its content in this plant is low. This has motivated the synthesis of this bioactive compound using yeast, tobacco, and Physcomitrium patens systems. However, the artemisinin production in these heterologous hosts is low and cannot fulfil its increasing clinical demand. Therefore, A. annua plants remain the major source of this bioactive component. Recently, the transcriptional regulatory networks related to artemisinin biosynthesis and glandular trichome formation have been extensively studied in A. annua. Various strategies including (i) enhancing the metabolic flux in artemisinin biosynthetic pathway; (ii) blocking competition branch pathways; (iii) using transcription factors (TFs); (iv) increasing peltate glandular secretory trichome (GST) density; (v) applying exogenous factors; and (vi) phytohormones have been used to improve artemisinin yields. Here we summarize recent scientific advances and achievements in artemisinin metabolic engineering, and discuss prospects in the development of high-artemisinin yielding A. annua varieties. This review provides new insights into revealing the transcriptional regulatory networks of other high-value plant-derived natural compounds (e.g., taxol, vinblastine, and camptothecin), as well as glandular trichome formation. It is also helpful for the researchers who intend to promote natural compounds production in other plants species.

Glandular and Eglandular Trichomes of Endemic Ballota glandulosissima (Lamiaceae)

The aim of this study is to determine the taxonomic importance of the glandular and eglandular trichomes on the vegetative and reproductive organs of Ballota glandulosissima. This species is endemic to Türkiye and the Eastern Mediterranean element. It is among the medicinal plants of Türkiye. On the vegetative and reproductive organs of the studied species, both glandular and eglandular trichomes were seen. These trichomes were examined using light and stereo microscopes. The glandular trichomes were divided into peltate and capitate. The eglandular trichomes were grouped as branched (stellate, bicellular, and multicellular) and unbranched (simple unbranched eglandular trichomes). The stalk cell number of capitate glandular trichomes shows changes. According to the number of stalk cells, capitate glandular trichomes were grouped into uni, bi, tri, and multi-cellular trichomes. In the taxon, dendroid trichomes were not observed on the vegetative and reproductive organs. The stellate trichomes were dense on the upper and lower surfaces of the leaf, and calyx teeth, while capitate glandular trichomes were dense on the petiole, stem, leaf, and outside part of the calyx, and calyx teeth. Peltate glandular trichomes are dense on the calyx and corolla. Especially, the capitate glandular and stellate trichomes are found to have significant taxonomic characteristics in distinguishing this species.

Applying quantitative spatial phenotypes analysis to the investigation of peltate glandular trichomes development pattern in Perilla frutescens.

Glandular trichomes, often referred to as "phytochemical factories", plays a crucial role in plant growth and metabolism. As the site for secretion and storage, the development of glandular trichomes is related to the dynamic biosynthesis of specialised metabolites. The study aims to explore the relationship between spatial phenotype and dynamic metabolism of glandular trichomes, and establish a novel approach for the exploration and study of the regulatory mechanism governing the development of glandular trichomes. In this study, we proposed a technical route based on the relative deviation value to distinguish the peltate glandular trichomes (PGTs) from the background tissues and extract their spatial phenotype. By defining glandular trichome developmental stages based on the leaf vein growth axis, we found that young PGTs were densely distributed near the proximal end of growth axis of the leaf veins, where perillaketone, a primary metabolite of PGTs, is predominantly accumulated. Conversely, mature PGTs are typically found near the distal end of the mid-vein growth axis and the lateral end of the secondary vein growth axis, where the accumulation rate of isoegomaketone and egomaketone exceeds that of perillaketone in PGTs. We further identified spatial phenotypic parameters, Lsum and d, as independent variables to construct a linear regression model that illustrates the relationship between the spatial phenotypes and metabolite content of PGTs, including perillaketone (R2 = 0.698), egomaketone (R2 = 0.593), isoegomaketone (R2 = 0.662) and the sum of the amount (R2 = 0.773). This model proved that the development of PGTs was correlated with the growth of the entire leaf, and the development stage of PGTs can be identifined by spatial phenotypes based on the leaf veins. In conclusion, the findings of this study enhance our understanding of correlation between spatial phenotype and development of glandular trichomes and offer a new approach to explore and study the regulatory mechanism of glandular trichome development.

Formation mechanism of glandular trichomes involved in the synthesis and storage of terpenoids in lavender

BackgroundLavender (genus Lavandula, family Lamiaceae) is an aromatic plant widely grown as an ornamental plant. The chemical composition of lavender is characterized by monoterpenoids, sesquiterpenoids, and other compounds, which are primarily synthesized and stored in epidermal secretory structures called glandular trichomes (GTs). Volatile organic compounds (VOCs) are responsible for the aroma characteristics of plant oil that drive consumer preference. Aroma is usually regarded as a characteristic trait for the classification of aromatic plants. Interestingly, VOCs are synthesized and stored in GTs. Lamiaceae species such as purple perilla, peppermint, basil, thyme, and oregano usually possess two types of GTs: peltate glandular trichomes (PGTs) and capitate glandular trichomes (CGTs). But the development process of PGTs in lavender has been reported in only a few studies to date.ResultsIn this study, we identified and quantified the VOCs in four lavender cultivars by headspace-solid phase micro extraction-gas chromatography mass spectrometry (HS–SPME–GC–MS). A total of 66 VOCs were identified in these four cultivars, the most prominent of which were linalyl acetate and linalool, and flowers were the main site of accumulation of these VOCs. Here, we examined the developmental process of PGTs, including the formation of their base, body, and apex. The apex cells contained secretory cavities, which produced VOCs. Based on the reference genome sequence of the lavender cultivar ‘Jingxun 2’, several R2R3-MYB subfamily genes related to GT formation were identified. These results will guide the engineering of GTs and molecular breeding of lavender for improving the VOC content.ConclusionsIn this study, we identified the VOCs in four lavender cultivars. We analyzed the formation of GTs, and compared the number and diameter size of PGTs among four lavender cultivars. Additionally, we identified four candidate genes belonging to the R2R3-MYB family.

The non-specific lipid transfer protein McLTPII.9 of Mentha canadensis is involved in peltate glandular trichome density and volatile compound metabolism.

Mentha canadensis L. is an important spice crop and medicinal herb with high economic value. The plant is covered with peltate glandular trichomes, which are responsible for the biosynthesis and secretion of volatile oils. Plant non-specific lipid transfer proteins (nsLTPs) belong to a complex multigenic family involved in various plant physiological processes. Here, we cloned and identified a non-specific lipid transfer protein gene (McLTPII.9) from M. canadensis, which may positively regulate peltate glandular trichome density and monoterpene metabolism. McLTPII.9 was expressed in most M. canadensis tissues. The GUS signal driven by the McLTPII.9 promoter in transgenic Nicotiana tabacum was observed in stems, leaves, and roots; it was also expressed in trichomes. McLTPII.9 was associated with the plasma membrane. Overexpression of McLTPII.9 in peppermint (Mentha piperita. L) significantly increased the peltate glandular trichome density and total volatile compound content compared with wild-type peppermint; it also altered the volatile oil composition. In McLTPII.9-overexpressing (OE) peppermint, the expression levels of several monoterpenoid synthase genes and glandular trichome development-related transcription factors-such as limonene synthase (LS), limonene-3-hydroxylase (L3OH), geranyl diphosphate synthase (GPPS), HD-ZIP3, and MIXTA-exhibited varying degrees of alteration. McLTPII.9 overexpression resulted in both a change in expression of genes for terpenoid biosynthetic pathways which corresponded with an altered terpenoid profile in OE plants. In addition, peltate glandular trichome density was altered in the OE plants as well as the expression of genes for transcription factors that were shown to be involved in trichome development in plants.

The form, dose, and method of application of vermicompost differentiate the phenylpropene biosynthesis in the peltate glandular trichomes of methylchavicol chemotype of Ocimum basilicum L.

Peltate glandular trichomes (PGTs) in basil (Ocimum basilicum L.) are ideal for studying phenylpropanoid metabolism, as they allow for the elimination of the effects of primary plant metabolism. In this study, we aimed to investigate the effects of 0, 10%, and 25% doses of both solid and tea forms of vermicompost on phenylpropanoid metabolism in PGTs of the methylchavicol chemotype of basil. The experiment based on the analysis of the gene expression (PAL, 4CL, EGS, EOMT, CVOMT) and the accumulation of phenylpropene (eugenol, chavicol, methyleugenol, methylchavicol) in PGTs after vermicompost treatment. Our results showed that the application of solid vermicompost (SV) to the root zone of basil at 10% and 25% significantly reduced the expression of EOMT and CVOMT to below 0.1 from 2.43 and 3.85, respectively. The application of 10% solid vermicompost (SV) to basil soil resulted in a decrease in methyleugenol and methylchavicol accumulation approximately by 50% and 52%, respectively. Further application of 25% (SV) resulted in a total decrease of approximately 76% and 51% in methyleugenol and methylchavicol accumulation, respectively. Application of 10% vermicompost tea (VT) to basil leaves resulted in a significant increase in chavicol accumulation (243%) and methyleugenol accumulation (613%) in basil essential oil, as well as upregulation of EOMT and CVOMT gene expression approximately by 391-fold and 1,155-fold, respectively, compared to control plants. Furthermore, application of 25% VT resulted in a significant increase in eugenol accumulation (665%) and methylchavicol accumulation (56%), as well as downregulation of EOMT and CVOMT gene expression approximately by 31-fold and 9-fold, respectively, compared to control plants. These findings suggest that VT application can modulate the accumulation of important phenylpropenes in basil through regulation of gene expression. In addition, the use of vermicompost tea has been shown to significantly enhance the levels of phenylpropenes in basil, which are important contributors to the herb's aroma and antimicrobial activity. This suggests that the application of VT can play a crucial role in determining the quality of basil in terms of its secondary metabolites, making it a valuable tool in phytoremediation practices. Overall, our results demonstrate the effectiveness of vermicompost on phenylpropene biosynthesis and the utility of PGTs composed of a single cell type for the study of secondary metabolic processes in plants.

Morphological characteristics, trichomes, and phytochemistry of inflorescences of Humulus lupulus L: Comparison of cropping systems and varieties

This study aimed to assess the influence of cropping systems (conventional and organic) and hops varieties ('Cascade', 'Chinook', 'Columbus', 'Hallertau Mittelfrüh', and 'Nugget') on morphological and anatomical aspects, as well as the contents of essential oil and phenolic compounds of hops inflorescences. Thus, morphological description and cone length; identification of trichomes and peltate glandular trichome density; anatomical and histochemical analysis of peltate glandular trichomes; essential oil content; and total phenolic compound content were evaluated. The results showed no influence of treatments on morphology; however, higher cone lengths were observed in organic cropping and in ‘Cascade’ and ‘Chinook’. These results report the first record of hops trichomes grown in Brazil. Three types of trichomes were identified in inflorescences: nonglandular, peltate, and bulbous glandular. An intense presence of peltate trichomes was observed on flowers. The trichome density in bracts differed among varieties, and 'Cascade' had the highest mean (8.19). There was a significant interaction between cropping systems and varieties for trichome density in flowers: with the exception of 'Nugget' (59.50), the varieties had higher means under organic cropping, especially 'Hallertau Mittelfrüh' (92.12) and 'Chinook' (88.12). Histochemical analysis revealed the presence of polysaccharides, starch, lipids, phenolic compounds, and proteins in peltate trichomes. The cropping systems did not affect the oil content, although there were significant differences between varieties. 'Hallertau Mittelfrüh' showed the lowest oil content (0.25%). Phenolic compounds showed no effect of treatments. Therefore, the results indicate that organic cropping and the 'Cascade' and 'Chinook' varieties are more promising under the conditions studied

Essential Oil from Fresh and Dry Leaves of Rosemary (Rosmarinus Officinalis L.): Antioxidant Activity and Microscopic Structure

Rosemary ( Rosmarinus officinalis L.) is a medicinal plant from the Lamiaceae family, originally from the Mediterranean region and can be found in most parts of the world. Rosemary essential oil is central to medication, personal health care, cosmetic ingredients, spices, and food preservation with considerable biological activities. This research aimed to measure the oil yield of fresh and dry rosemary leaf samples, identify the chemical constituents of the oil, measure the antioxidant activity of the oil, and analyze the secretory cells of the leaves. These are important to support the development and deployment of rosemary essential oil. The method of drying leaf samples is essential for preserving the oil compounds and it influences both essential oil yield and antioxidant activity. Rosemary leaves were harvested from the field of Dasong Village, Sub-District of Sukasada, and the District of Buleleng, Bali, Indonesia. One part (5 kg) of the leaves samples was naturally dried at room temperature at natural atmospheric pressure for seven days and this was referred to shade drying. Another part of the leaf samples (5 kg) was freshly processed. Both shade-dried and freshly harvested rosemary leaves were extracted using steam distillation with three replications. The composition of the essential oils was determined using Gas Chromatography-Mass Spectrometry. Cross-sections of the leaves were prepared by the paraffin embedding method and stained with safranin. Leaf microscopic structure was observed under a light microscope. This study confirmed that the yields of essential oils from dry leaf samples were higher than fresh samples (0.56% and 0.36%, respectively). The oil from fresh and dry leaves contained 183 and 164 compounds respectively. The main constituents of both oils were eucalyptol, α-pinene, geraniol, linalool, and caryophyllene. The novelty of this study was that both oils from fresh and dry leaf samples have the same strong antioxidant activity with IC 50 of 83.08 ppm. This might be useful for the utilization of the oil for different purposes. The secretory structure of the essential oil was glandular trichomes of two types: peltate and capitate. Keywords: capitates glandular trichomes, essential oil, peltate glandular trichomes, Rosemarinus officinalis , steam distillation. https://doi.org/10.55463/issn.1674-2974.50.3.9

Morphology and mass spectrometry-based chemical profiling of peltate glandular trichomes on Mentha haplocalyx Briq leaves

Mentha haplocalyx Briq (M. haplocalyx) is a herbaceous plant that has long been used as a food, medicinal spice, and flavoring agent in traditional Chinese medicine. Its secondary metabolites, having high commercial values, are mainly produced in tiny specialized structures called glandular trichomes (GTs). The primary purpose of this study was to examine the morphology and metabolites of peltate GTs in M. haplocalyx.Peltate GTs possessed globular dome shapes and intense auto-fluorescence on the surfaces of M. haplocalyx leaves. Structure subsidence and cuticle rupture were found throughout the aging stage of peltate GTs. According to histochemical staining results, the secretion of peltate GTs contained anthraquinone, flavonoids, phenolic acid and terpenoids. In M. haplocalyx peltate GTs and leaf tissues without peltate glandular trichomes, ten and two volatile compounds were identified respectively. Peltate GTs contained 42 non-volatile chemicals with a variety of structural types, including 20 flavonoids, 17 phenolic acids,1 diterpene, 3 anthraquinone and 1 alkane. Meanwhile, 15 non-volatile compounds were discovered in leaf tissues without peltate glandular trichomes, and they were all included in the list of peltate GTs' 41 components. Therefore, Peltate GTs were shown to be the primary site of not just volatile compounds but also non-volatile chemicals in M. haplocalyx. This study provides an important theoretical basis and technical approach for clarifying the bio-active metabolite biosynthesis in M. haplocalyx.

Cloning of StHD1 and StHD8 from Schizonepeta tenuifolia and function of regulating glandular trichome development

Hd-Zip, a unique transcription factor in plant kingdom, influences the growth, development, and secondary metabolism of plants. Hd-zip Ⅳ is thought to play an important role in trichome development of Schizonepeta tenuifolia. This study aims to explore the functions of StHD1 and StHD8 in Hd-zip Ⅳ subfamily in peltate glandular trichome development. To be specific, the expression patterns of the two genes and interaction between the proteins encoded by them were analyzed based on transcriptome sequencing and two-hybrid screening. The subcellular localization was performed and functions of the genes were verified in tobacco and S. tenuifolia. The results showed that StHD1 and StHD8 had high similarity to HD-Zip Ⅳ proteins of other plants and they all had the characteristic conserved domains of HD-Zip Ⅳ subfamily. They were located in the nucleus. The two genes mainly expressed in young tissues and spikes, and StHD1 and StHD8 proteins interacted with each other. The density and length of glandular trichomes increased significantly in tobacco plants with the overexpression of StHD1 and StHD8. Inhibiting the expression of StHD1 and StHD8 by VIGS(virus-induced gene silencing) in S. tenuifolia resulted in the reduction in the density of peltate glandular trichomes, the expression of key genes related to mono-terpene synthesis, and the relative content of limonene and pulegone, the main components of monoterpene. These results suggested that StHD1 and StHD8 of S. tenuifolia formed a complex to regulate glandular trichomes and affect the biosynthesis of monoterpenes.

Single-cell transcriptome of Nepeta tenuifolia leaves reveal differentiation trajectories in glandular trichomes.

The peltate glandular trichomes (PGTs) on Nepeta tenuifolia leaves can secrete and store bioactive essential oils. ScRNA-seq is a powerful tool for uncovering heterogeneous cells and exploring the development and differentiation of specific cells. Due to leaves rich in PGTs, the young leaves were used to isolated protoplasts and successfully captured 33,254 protoplasts for sequencing purposes. After cell type annotation, all the cells were partitioned into six broad populations with 19 clusters. Cells from PGTs were identified based on the expression patterns of trichome-specific genes, monoterpene biosynthetic genes, and metabolic analysis of PGT secretions. The developmental trajectories of PGTs were delineated by pseudotime analysis. Integrative analysis of scRNA-seq data from N. tenuifolia leaves and Arabidopsis thaliana shoot revealed that PGTs were specific to N. tenuifolia. Thus, our results provide a promising basis for exploring cell development and differentiation in plants, especially glandular trichome initiation and development.

Alteration in Light Spectra Causes Opposite Responses in Volatile Phenylpropanoids and Terpenoids Compared with Phenolic Acids in Sweet Basil (Ocimum basilicum) Leaves.

Basil (Ocimum basilicum, cv. Dolly) grew under three different light spectra (A, B, and C) created by light-emitting diode lamps. The proportions of UV-A, blue, and green-yellow wavelengths decreased linearly from A to C, and the proportions of red and far-red wavelengths increased from A to C. Photosynthetic photon flux density was 300 μmol m–2 s–1 in all spectra. The spectrum C plants had highest concentrations of phenolic acids (main compounds: rosmarinic acid and cichoric acid), lowest concentrations and emissions of phenylpropanoid eugenol and terpenoids (main compounds: linalool and 1,8-cineole), highest dry weight, and lowest water content. Conversely, spectra A and B caused higher terpenoid and eugenol concentrations and emissions and lower concentrations of phenolic acids. High density of peltate glandular trichomes explained high terpenoid and eugenol concentrations and emissions. Basil growth and secondary compounds affecting aroma and taste can be modified by altering light spectra; however, increasing terpenoids and phenylpropanoids decreases phenolic acids and growth and vice versa.

Identification and characterization of a novel gene involved in glandular trichome development in Nepeta tenuifolia.

Nepeta tenuifolia is a medicinal plant rich in terpenoids and flavonoids with antiviral, immunoregulatory, and anti-inflammatory activities. The peltate glandular trichome (PGT) is a multicellular structure considered to be the primary storage organ for monoterpenes; it may serve as an ideal model for studying cell differentiation and the development of glandular trichomes (GTs). The genes that regulate the development of GTs have not yet been well studied. In this study, we identified NtMIXTA1, a GT development-associated gene from the R2R3 MYB SBG9 family. NtMIXTA1 overexpression in tobacco resulted in the production of longer and denser GTs. Virus-induced gene silencing of NtMIXTA1 resulted in lower PGT density, a significant reduction in monoterpene concentration, and the decreased expression of genes related to monoterpene biosynthesis. Comparative transcriptome and widely targeted metabolic analyses revealed that silencing NtMIXTA1 significantly influenced the expression of genes, and the production of metabolites involved in the biosynthesis of terpenoids, flavonoids, and lipids. This study provides a solid foundation describing a mechanism underlying the regulation of GT development. In addition, this study further deepens our understanding of the regulatory networks involved in GT development and GT development-associated metabolite flux, as well as provides valuable reference data for studying plants with a high medicinal value without genetic transformation.

Anatomy, trichome micromorphology and phytochemical profile of Stachys rizeensis R.Bhattacharjee from Turkey

In recent years, the popularity of natural products and natural product formulations has increased due to their beneficial effects on health. As a part of this trend, Lamiaceae family members have attracted attention due to their rich bioactive properties. Although the Stachys rizeensis R.Bhattacharjee plant is an endemic plant species in Turkey, no studies focus on its characterization. Hence, the present study aims to demonstrate the anatomical, morphological and phytochemical characterization of S. rizeensis in Turkey. In the first stage of the study, anatomical and trichome morphological characterization was performed to contribute to the taxonomic definition of S. rizeensis was found to be anatomically different from some other previously studied Stachys sp. by showing lacunar collenchyma type, uncertain cambium at the corners, two or three rows of endodermis in certain areas in the stem and two rows of palisade parenchyma, capitate and peltate glandular trichomes in the leaf. In the second stage, the phenolic profile, total phenolic/flavonoid content and antioxidant activity of the plant extracts prepared using solvents with different polarities (ethanol, methanol, water, ethyl acetate and hexane) were tested to determine the phytochemical content of the plant. The phytochemical analysis supported by chemometric analysis (PCA and HCA) revealed that methanol was the most efficient organic solvent for the extraction of the phytochemical compounds of the plant. Additionally, it was observed that chlorogenic acid (1842.40–217,086.19 mg/kg), verbascoside (2591.43–204,429.81 mg/kg), luteolin (3579.56–88,636.14 mg/kg) and kaempferol (9706.30–50,340.93 mg/kg) compounds were present at maximum levels in this plant, in which 31 different phenolic compounds were scanned using LC-MS/MS. In addition, results obtained from the phytochemical analysis revealed that S. rizeensis is a valuable plant that can be used for medical protection/treatment and that it could also have a variety of culinary applications. The present study served as the first original report regarding the chemical profile and anatomical characteristics of S. rizeensis (Lamiaceae) from Turkey.