Secretory Trichomes Research Articles

Leaf micromorphology and anatomical traits of leaves as potential taxonomic markers for infrageneric classification of<em> Cinnamomum</em> (Lauraceae)

This study aimed to examine the leaf anatomy of the eight species of Cinnamomum (family Lauraceae) that occur in Sri Lanka to evaluate its potential utility in taxonomic delimitation. Leaf surface micromorphology and internal anatomy were studied using standard light and scanning electron microscopy. Infrageneric and interspecific variation in micromorphology of cuticular materials was observed in both abaxial and adaxial surfaces. Both abaxial and adaxial surfaces had undulating, thick cuticles with different patterns of wax deposition. Leaves were hypostomatic with no special arrangement for epidermal pavement cells. Simple, unicellular, unbranched, solitary and non-glandular trichomes were observed in different species on both surfaces of the leaves. Both adaxial and abaxial surfaces in C. dubium and C. capparu-coronde were densely covered with simple, unicellular/ falcate, long and thin trichomes. Transverse sections (TS) of the leaves were different in shape (symmetrical, asymmetrical, irregular, saucer). The midrib contained one open arch central vascular bundle that was different in shape (oval, elongated, irregular, ‘V’shaped, partially dissected into 2 or 3 segments) in different species. The number of collateral vessels was dissimilar between the species and varied in number (±10 - ±17). Isolated or aggregated crystals were observed in different parts of the leaf and oval-to-round schizogenous secretory cells were present in C. capparu-coronde, C. citriodorum and C. dubium. Leaf cuticular features together with the presence/absence of secretory cavities, trichome shape and density, midrib cross-section outline and shape of vascular bundles are taxonomically informative characteristics that can be used to differentiate the eight species of Cinnamomum that occur in Sri Lanka.

New insight in secretory structures and secretion composition in Rhus typhina L. – Anatomical, histochemical, and ultrastructural studies

Rhus typhina is a valuable plant used in the pharmaceutical, cosmetic, and food industries due to the presence of biologically active substances accumulated in its organs, especially in secretory structures, i.e. trichomes and secretory ducts. Light microscopy, scanning electron microscopy, and transmission electron microscopy were used to examine the structure of glandular and non-glandular trichomes, as well as secretory ducts present in inflorescence peduncles of R. typhina. The chemical composition of the secretion produced by trichomes and ducts was assessed using histochemical techniques, including observations under brightfield and fluorescence microscopes. Two types of capitate glandular trichomes producing secretions with a similar composition and non-glandular trichomes exhibiting secretory activity were identified. The secretion of glandular trichomes was dominated by acidic and neutral lipids, essential oil, sesquiterpenes, and steroid-containing terpenes. The schizogenic secretory ducts located in the phloem produced a viscous milky substance with acidic polysaccharides, acidic lipids, phenolic compounds, and proteins. The secretion was released into the duct lumen through notches in the walls of the secretory epithelial cell facing the duct lumen. The location, type, and traits of the non-glandular trichomes and secretory structures, as well as the composition of the secreted products are considered important taxonomic features in the family Anacardiaceae and the Rhus genus. Additionally, these characters are important diagnostic markers for the pharmacobotanical identification of the species in medicinal and cosmetic raw materials. The various compounds present in the secretory structures of R. typhina may contribute to plant protection against pathogens or herbivory and probably play a role as attractants for pollinators and seed dispersers.

Application and Evaluation of the Antifungal Activities of Glandular Trichome Secretions from Air/Sun-Cured Tobacco Germplasms against Botrytis cinerea.

The secretions of the glandular trichomes of tobacco leaves and flowers contain abundant secondary metabolites of different compounds, such as cebradanes, labdanes, and saccharide esters. These secondary metabolites have shown interesting biological properties, such as antimicrobial, insecticidal, and antioxidant activity. In this study, 81 air/sun-cured tobacco germplasms were used as experimental materials. Quantitative and qualitative analyses of the glandular secretion components were conducted using ultra-performance liquid chromatography-quadrupole-time of flight-mass spectrometry (UPLC-Q-TOF MS) and gas chromatography-mass spectrometry (GC-MS). The ethanol extracts of glandular trichomes from tobacco leaves and flowers were evaluated for antifungal activity against the fungus Botrytis cinerea using the mycelial growth rate method. Orthogonal Partial Least Squares (OPLS) analysis was then performed to determine the relationship between the trichome secretion components and their anti-fungal activity. The results showed significant differences among the antifungal activities of the tested ethanol extracts of tobacco glandular trichomes. The inhibition rates of the upper leaves and flower extracts against B. cinerea were significantly higher than those of the middle and lower leaves, and 59 germplasms (73.75% of the tested resources) showed antifungal rates higher than 50%, with four germplasms achieving a 95% antifungal rate at the same fresh weight concentration (10 mg/mL). The OPLS analysis revealed that the antifungal activity was primarily associated with alpha-cembratriene-diol (α-CBT-diol (Peak7)) and beta-cembratriene-diol (β-CBT-diol (Peak8)), followed by sucrose esters III (SE(III)) and cembratriene-diol oxide. These findings help identify excellent tobacco germplasms for the development and utilization of botanical pesticides against fungi and provide a theoretical reference for the multipurpose utilization of tobacco germplasms.

The AaBBX21-AaHY5 module mediates light-regulated artemisinin biosynthesis in Artemisia annua L.

The sesquiterpene lactone artemisinin is an important anti-malarial component produced by the glandular secretory trichomes of sweet wormwood (Artemisia annua L.). Light was previously shown to promote artemisinin production, but the underlying regulatory mechanism remains elusive. In this study, we demonstrate that ELONGATED HYPOCOTYL 5 (HY5), a central transcription factor in the light signaling pathway, cannot promote artemisinin biosynthesis on its own, as the binding of AaHY5 to the promoters of artemisinin biosynthetic genes failed to activate their transcription. Transcriptome analysis and yeast two-hybrid screening revealed the B-box transcription factor AaBBX21 as a potential interactor with AaHY5. AaBBX21 showed a trichome-specific expression pattern. Additionally, the AaBBX21-AaHY5 complex cooperatively activated transcription from the promoters of the downstream genes AaGSW1, AaMYB108, and AaORA, encoding positive regulators of artemisinin biosynthesis. Moreover, AaHY5 and AaBBX21 physically interacted with the A. annua E3 ubiquitin ligase CONSTITUTIVELY PHOTOMORPHOGENIC 1 (COP1). In the dark, AaCOP1 decreased the accumulation of AaHY5 and AaBBX21 and repressed the activation of genes downstream of the AaHY5-AaBBX21 complex, explaining the enhanced production of artemisinin upon light exposure. Our study provides insights into the central regulatory mechanism by which light governs terpenoid biosynthesis in the plant kingdom.

AaGL3-like is jasmonate-induced bHLH transcription factor that positively regulates trichome density in Artemisia annua

The leaves of Artemisia annua contain GSTs (Glandular secretory trichomes) that can secrete and store artemisinin, the drug most effective for treating uncomplicated malaria. Therefore, increasing the density of GSTs in A. annua is an efficient way to enhance artemisinin content. However, our understanding of how GSTs develop still needs to be improved. Here, we isolated an A. annua homolog of AtGL3 (GLABRA3), known as AaGL3-like, that positively regulates trichome density in A. annua. AaGL3-like is nuclear-localized and transcriptionally active. It is least expressed in roots and most prominently in aerial components like leaves, stems, and inflorescence. Under JA and GA hormonal treatments, AaGL3-like expression is significantly increased. In transgenic over-expression AaGL3-like lines, trichome developmental genes such as AaHD1 and AaGSW2 showed much increased expression. The AaGL3RNAi line exhibited considerably lower levels of AaHD1 and AaGSW2 transcripts. As a result, the AaGL3-RNAi lines showed reduced levels of artemisinin content and trichome density compared to wild-type and overexpression lines. Additionally, we have found that when co-expressed with AaJAZ8, the induction of trichome developmental genes was reduced as compared to individual OEAaGL3-like lines. Further, AaJAZ8 directly binds to AaGL3-like in the Y2H assay. These findings suggest that AaGL3-like is a jasmonate-induced bHLH transcription factor that drastically increases the final accumulation of artemisinin content by regulating trichome density in A. annua.

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.

Effects of co-overexpression of ALDH1, CYP71AV1, and iaaM on the density, length, and width of glandular secretory trichomes and the contents of artemisinin in Artemisia annua

Sesquiterpene lactone artemisinin is one of the main agents used to treat malaria. Artemisinin is produced in the glandular secretory trichomes (GSTs) of Artemisia annua. The plant hormones and metabolic pathways regulate the artemisinin content of A. annua. It was possible to examine the functions of auxin, an important plant hormone, in the development of GSTs in A. annua by enhancing the expression of iaaM, which encodes a tryptophan monooxygenase involved in the biosynthesis of auxin. Additionally, the effects of co-overexpression of aldehyde dehydrogenase 1 ( ALDH1), P450 monooxygenase ( CYP71AV1), and iaaM on the density, length, and width of GSTs and the contents of artemisinin were further investigated. Results indicated that overexpression of iaaM might increase the density, length, and width of GSTs by enhancing auxin biosynthesis. This study also proved the key regulatory role of ALDH1 in the biosynthesis of artemisinin. Moreover, co-overexpression of ALDH1, CYP71AV1, and iaaM successfully increased the density, length, and width of GSTs and improved the artemisinin content in A. annua. Therefore, we established a theoretical basis for modifying artemisinin accumulation in this study by regulating the expression of auxin and artemisinin synthesis-related genes using a metabolic engineering method.

A Study on Justicia flava (Forssk.) Vahl.: Pharmacognostic Characterization and Antiplasmodial and Anti-Inflammatory Properties of the Leaves

Justiciaflava (Acanthaceae) is utilized in folk medicine for treating malaria, inflammatory conditions, and respiratory infections. In this study, the antiplasmodial and anti-inflammatory activities of the 70% hydroalcoholic leaf extract of J. flava (JFE) were investigated. The antiplasmodial activity was assessed by the suppressive test and Rane’s curative test. The carrageenan-induced paw oedema assay in chicks was used to assess the anti-inflammatory activity. In Rane’s curative test, JFE significantly suppressed the parasitaemia level ( p < 0.0001) by 56.85%, 63.85%, and 77.85% at 30, 100, and 300 mg·kg−1, respectively. The highest suppression of parasitaemia in the suppressive test was 51.31% at 300 mg·kg−1. The extract prolonged the survival time of infected mice significantly and prevented weight loss and hypothermia which are cardinal signs of P. berghei-induced infection. JFE inhibited foot oedema in chicks with a maximum percentage inhibition of 54.00 ± 5.20%. Pharmacognostic characterization of J. flava revealed it to have simple, petiolate, oppositely arranged leaves which are broadly lanceolate in shape with entire to slightly crenate margins. Microscopy of the leaf showed wavy-walled epidermal cells, diallelocytic stomata, abundant clothing and secretory trichomes, pitted vessels, collateral conjoint vascular bundles, cystoliths, and prismatic calcium oxalate crystals. Flavonoids, tannins, phytosterols, triterpenoids, coumarins, alkaloids, and saponins were detected in the plant. This study has provided important parameters for the correct identification of J. flava and given the scientific credence to its antimalarial and anti-inflammatory effects in traditional medicine. J. flava is a potential source of new antimalarial and anti-inflammatory compounds.

Graphene enhances artemisinin production in the traditional medicinal plant Artemisia annua via dynamic physiological processes and miRNA regulation

We investigated the effects of graphene on the model herb Artemisia annua, which is renowned for producing artemisinin, a widely used pharmacological compound. Seedling growth and biomass were promoted when A. annua was cultivated with low concentrations of graphene, an effect which was attributed to a 1.4-fold increase in nitrogen uptake, a 15%–22% increase in chlorophyll fluorescence, and greater abundance of carbon cycling–related bacteria. Exposure to 10 or 20 mg/L graphene resulted in a ∼60% increase in H2O2, and graphene could act as a catalyst accelerator, leading to a 9-fold increase in catalase (CAT) activity in vitro and thereby maintaining reactive oxygen species (ROS) homeostasis. Importantly, graphene exposure led to an 80% increase in the density of glandular secreting trichomes (GSTs), in which artemisinin is biosynthesized and stored. This contributed to a 5% increase in artemisinin content in mature leaves. Interestingly, expression of miR828 was reduced by both graphene and H2O2 treatments, resulting in induction of its target gene AaMYB17, a positive regulator of GST initiation. Subsequent molecular and genetic assays showed that graphene-induced H2O2 inhibits micro-RNA (miRNA) biogenesis through Dicers and regulates the miR828–AaMYB17 module, thus affecting GST density. Our results suggest that graphene may contribute to yield improvement in A. annua via dynamic physiological processes together with miRNA regulation, and it may thus represent a new cultivation strategy for increasing yield capacity through nanobiotechnology.

MORPHOLOGICAL FEATURES AND PRODUCTIVITY OF THE ATROPA L. GENUS SPECIES, CULTIVATED IN THE MOSCOW REGION

Background. The application of the anatomical method of studying various forms, varieties and species will allow to determine the degree of plant adaptation to habitat conditions and to assess its ecological plasticity.
 Purpose. This work aim is to evaluate the species and breeding samples of the Atropa genus by a set of signs, including morphological description, shape, size and weight of leaves, the nature of the pubescence of the leaf plade epidermis, location, size and number of stomata, as well as the yield of raw materials.
 Results. All collection samples of the studied species of the genus Atropa in the conditions of the Non-Chernozem zone of the Russian Federation undergo a full cycle of development. The assessment of the potential resistance of 14 forms and species of belladonna to unfavorable biotic and abiotic environmental factors was carried out, their main morpho-anatomical features were studied. The adaptive potential of the leaves of the studied Atropa plants is due to the variability of the structural elements of the leaf epidermis and is one of the factors of resistance to stress. In the group of studied samples, A. acuminata (406, Lithuania) and A. belladonna (487, Poland) have the lowest stress-adaptive potential (according to the set of signs). It was noted that populations of A. belladonna from Eastern Europe and France have signs of xeromorphism against the background of a decrease in plant size compared to the control and the lowest yield. It is noted that A. belladonna samples from Europe with yellow corolla staining occupy an intermediate value in yield in the presence of xeromorphic signs, which indicates their adaptability to the conditions of agrocenosis. The presence of numerous secreting trichomes in the studied accessions of A. belladonna and A. komarovii (nos. 5 and 14) may indicate their potential resistance to diseases and pests. The A. caucasica and A. komarovii species, as well as the A. belladonna specimen from Great Britain (no. 1), can be considered well adapted.
 Conclusion. The highest-yielding populations are from Russia A. belladonna 15/15; A. caucasica 118 compared to the Bagira variety. These samples can be considered promising and well-adapted candidates for creating a new variety of A. belladonna.

Identification and Evaluation of Diterpenoids from Glandular Trichome Secretions of Air/Sun-Cured Tobacco Germplasm Resources

To explore the multipurpose utilization of tobacco germplasm resources, 80 representative air/sun-cured tobacco germplasms were used as experimental materials to determine the composition and content of the diterpenoids of glandular trichome secretions using ultra-performance liquid chromatography (UPLC). Correlation analysis, cluster analysis, and principal component analysis (PCA) were used to comprehensively evaluate 80 air/sun-cured tobacco germplasms. The results are as follows: (1) 11 chromatographic peaks (Peak1–Peak11) were detected by UPLC, and the coefficient of variation of their contents ranged from 26.3 to 143%. (2) Correlation analysis showed that alpha-cembratriene-diol (α-CBT-diol) and beta-cembratriene-diol (β-CBT-diol) had the highest correlation coefficients (0.97), showing a significantly negative correlation with cis-abienol and a significantly positive correlation with the other diterpenoids. (3) PCA showed that the cumulative contribution rate of the three principal components was 75.70%, and the diterpenoid-rich germplasms were ranked in the following order: X40 (Maiduo) > X48 (Jianpingpiaoba) > X58 (Mianzhu) > X54 (Shifangpipaliu) > X63 (Xuejia5) > X41 (Tangpeng) > X29 (OLOR) > X73 (Criollo) > X44 (Tiebanqing) > X70 (Nicaragua Changxin). The diterpenoid content of X36 was the lowest. These results provide excellent germplasms for plant-based pesticides and fragrance compounds and genetic studies of the diterpenoid metabolism.

Leaf secretory structures in Rosa lucieae (Rosaceae): two times of secretion-two ecological functions?

Secretory trichomes and colleters are two of the secretory structures whose exudates may cover thebody of the plant. Such secretions comprise resins or mucilages which are associated with an array of ecological roles. In Rosaceae, secretory trichomes have been reported for the leaves while colleters associated with leaf teeth. Our study aimed to identify the secretory structures of Rosa lucieae and understand the ecological role played by these glands as interpreted by morphoanatomical and histochemical studies. Samples from developing and fully mature leaves were collected, fixed, and processed according to usual techniques for light and scanning electron microscopy. In R. lucieae, colleters are restricted to the leaf and stipular margins and are associated with the teeth. They present a parenchymatous axis surrounded by a secretory palisade epidermis and usually fall off after the secretory activity is finished. Different from colleters, secretory trichomes are persistent. They present a multicellular secretory head and stalk. They are found at the base of the leaflet, petiolule, rachis, and petiole and occasionally on the stipular and leaf margins. The colleters predominantly secrete mucilages while the secretory trichomes secrete lipids and terpenes, both via cuticle rupture. The secretory activity of colleters is predominant in the leaf primordia, holding leaflets together and protecting meristems and leaves from desiccation, while the secretory trichomes maintain their secretory activity at different stages of leaf development, protecting different regions of the leaf against pathogens and herbivores.

Chromatin architecture of two different strains of Artemisia annua reveals the alterations in interaction and gene expression.

The hierarchical architecture of chromatins affects the gene expression level of glandular secreting trichomes and the artemisinin biosynthetic pathway-related genes, consequently bringing on huge differences in the content of artemisinin and its derivatives of A. annua. The plant of traditional Chinese medicine "Qinghao" is called Artemisia annua L. in Chinese Pharmacopoeia. High content and the total amount of artemisinin is the main goal of A. annua breeding, nevertheless, the change of chromatin organization during the artemisinin synthesis process has not been discovered yet. This study intended to find the roles of chromatin structure in the production of artemisinin through bioinformatics and experimental validation. Chromosome conformation capture analysis was used to scrutinize the interactions among chromosomes and categorize various scales of chromatin during artemisinin synthesis in A. annua. To confirm the effect of the changes in chromatin structure, Hi-C and RNA-sequencing were performed on two different strains to find the correlation between chromatin structure and gene expression levels on artemisinin synthesis progress and regulation. Our results revealed that the frequency of intra-chromosomal interactions was higher in the inter-chromosomal interactions between the root and leaves on a high artemisinin production strain (HAP) compared to a low artemisinin production strain (LAP). We found that compartmental transition was connected with interactions among different chromatins. Interestingly, glandular secreting trichomes (GSTs) and the artemisinin biosynthetic pathway (ABP) related genes were enriched in the areas which have the compartmental transition, reflecting the regulation of artemisinin synthesis. Topologically associated domain boundaries were associated with various distributions of genes and expression levels. Genes associated with ABP and GST in the adjacent loop were highly expressed, suggesting that epigenetic regulation plays an important role during artemisinin synthesis and glandular secreting trichomes production process. Chromatin structure could show an important status in the mechanisms of artemisinin synthesis process in A. annua.

The Light- and Jasmonic Acid-Induced AaMYB108-like Positive Regulates the Initiation of Glandular Secretory Trichome in Artemisia annua L.

The plant Artemisia annua L. is famous for producing "artemisinin", which is an essential component in the treatment of malaria. The glandular secretory trichomes (GSTs) on the leaves of A. annua secrete and store artemisinin. Previous research has demonstrated that raising GST density can effectively raise artemisinin content. However, the molecular mechanism of GST initiation is not fully understood yet. In this study, we identified an MYB transcription factor, the AaMYB108-like, which is co-induced by light and jasmonic acid, and positively regulates glandular secretory trichome initiation in A. annua. Overexpression of the AaMYB108-like gene in A. annua increased GST density and enhanced the artemisinin content, whereas anti-sense of the AaMYB108-like gene resulted in the reduction in GST density and artemisinin content. Further experiments demonstrated that the AaMYB108-like gene could form a complex with AaHD8 to promote the expression of downstream AaHD1, resulting in the initiation of GST. Taken together, the AaMYB108-like gene is a positive regulator induced by light and jasmonic acid for GST initiation in A. annua.

Roles and Preliminary Mechanism of Tobacco cis-Abienol in Inducing Tomato Resistance against Bacterial Wilt.

Bacterial wilt negatively impacts the yield and quality of tomatoes. cis-Abienol, a labdane diterpenoid abundantly produced in the trichome secretion of Nicotiana spp., can induce bacterial wilt resistance in plants; however, study on its practical application and acting mechanism is very limited. This study established the application conditions of cis-abienol for inducing tomato bacterial wilt resistance by pot-inoculation experiments and investigated the underlying mechanism by determining the physio-biochemical indexes and transcriptomic changes. The results showed that applying cis-abienol to the roots was the most effective approach for inducing tomato bacterial wilt resistance. The optimal concentration was 60 μg/mL, and 2-3 consecutive applications with 3-6 days intervals were sufficient to induce the bacterial wilt resistance of tomato plants. cis-Abienol could enhance the antioxidant enzyme activity and stimulate the defensive signal transduction in tomato roots, leading to the upregulation of genes involved in the mitogen-activated protein kinase cascade. It also upregulated the expression of JAZ genes and increased the content of jasmonic acid (JA) and salicylic acid (SA), which control the expression of flavonoid biosynthetic genes and the content of phytoalexins in tomato roots. cis-Abienol-induced resistance mainly depends on the JA signalling pathway, and the SA signalling pathway is also involved in this process. This study established the feasibility of applying the plant-derived terpenoid cis-abienol to induce plant bacterial wilt resistance, which is of great value for developing eco-friendly bactericides.

Glandular and Non-Glandular Trichomes from Phlomis herba-venti subsp. pungens Leaves: Light, Confocal, and Scanning Electron Microscopy and Histochemistry of the Secretory Products.

The purpose of this paper is to highlight the morphological peculiarities of glandular and non-glandular trichomes from leaves of Phlomis herba-venti subsp. Pungens using light, confocal, and scanning electron microscopy. Histochemistry techniques were used to analyze the localization of different chemical compounds in secretory trichomes. Two types of non-glandular trichomes were identified: unicellular and branched. They were found more frequently on the lower epidermis of leaves in different stages of ontogenetic development. Glandular trichomes were categorized as capitate (C1 and C2) with different stalk lengths and one-four secretory cells and dendroids (D) with one-four secretory cells. The histochemical analyses revealed distinct secretory products in terms of composition and distribution among the three types of glandular trichomes. The dendroid category of glandular trichomes is rarely found in plants and is not characteristic of the Lamiaceae species. They were described and characterized from a micromorphological and histochemical point of view for the first time in P. herba-venti.

Investigating the Physiological and Molecular Responses of Solanum lycopersicum hp Mutants to Light of Different Quality for Biotechnological Applications.

The effect of the light of different spectral compositions, white fluorescent light (WFL), red light (RL, 660 nm), blue light (BL, 450 nm), green light (GL, 525 nm), and white LED light (WL, 450 + 580 nm), on the physiological parameters of Solanum lycopersicum 3005 hp-2 (defective for a DET1 gene) and 4012 hp-1w; 3538 hp-1; 0279 hp-1.2 (defective for a DDB1a gene) photomorphogenetic mutants was studied. The parameters of the primary photochemical processes of photosynthesis, photosynthetic and transpiration rates, the antioxidant capacity of low-molecular weight antioxidants, the content of the total phenolic compounds, including flavonoids, and the expression of the genes involved in light signaling and biosynthesis of secondary metabolites were determined. Under BL, the 3005 hp-2 mutant showed the highest nonenzymatic antioxidant activity, which occurred to a greater extent due to the increase in flavonoid content. At the same time, under BL, the number of secretory trichomes on the surface of the leaves of all mutants increased equally. This suggests the accumulation of flavonoids inside leaf cells rather than in trichomes on the leaf surface. The data obtained indicate the possibility of using the hp-2 mutant for biotechnology to increase its nutritional value by enhancing the content of flavonoids and other antioxidants by modulating the spectral composition of light.

Nitric oxide induces antioxidant machinery, PSII functioning and artemisinin biosynthesis in Artemisia annua under cadmium stress

Soil contamination by heavy metals poses a significant environmental challenge, as the practical implementation of existing remediation technologies in the field has encountered numerous obstacles. This has necessitated the requirement of finding alternate solutions to reduce the harm caused to plants. In this study, nitric oxide (NO) was investigated for its potential to reduce cadmium (Cd) toxicity in A. annua plants. Although NO plays a vital role in the growth and development of plants, information on its role in reducing abiotic stress in plants is limited. A. annua plants were exposed to 20 and 40 mg/kg Cd regardless of the addition of exogenous sodium nitroprusside (SNP), a NO donor, at 200 µM concentration. Results showed that SNP treatment improved plant growth, photosynthesis, chlorophyll fluorescence, pigment content, and artemisinin production while reducing Cd accumulation and improving membrane stability in A. annua during Cd stress. The results demonstrated that NO can effectively reverse Cd-induced damage in A. annua by modulating the antioxidant system, maintaining redox homeostasis, and improving photosynthetic performance and different fluorescence parameters such as Fv/Fm, ФPSII, and ETR. The supplementation of SNP caused a substantial improvement in chloroplast ultrastructure, stomatal behavior, and different attributes relate to glandular secretory trichomes, which in turn increased artemisinin production; 14.11 % in plants exposed to Cd stress of 20 mg/kg. Our findings highlight that NO could be useful in mediating the repair of Cd-induced damage to A. annua, and suggest that it may play a critical role in plant signaling networks, improving plant adaptability to Cd stress. The results have important implications for developing new strategies to mitigate the negative impacts of environmental contaminants on plant health, and ultimately, the ecosystem.

A contribution of leaf anatomy to the taxonomy of Varronia P. Browne (Cordiaceae, Boraginales)

Varronia (Cordiaceae, Boraginales) is a Neotropical genus of approximately 125 species. In Brazil, it is represented by 36 species, of which 21 are endemic. Regarding the vegetative organs, their species are morphologically similar, and despite recent revision studies on the genus, the identification and delimitation of some species are still problematic. In this perspective, we here investigate the leaf anatomy of ten species of Varronia recorded in Brazil, to detect diagnostic taxonomic characters and putative synapomorphies for the genus. The types and distribution of secretory and non-secretory trichomes were identified as one of the most relevant characters in differentiating the studied species. Three types of non-secretory and one type of secretory trichomes are reported in the genus for the first time. The occurrence of crystalline sand in the mesophyll was identified as a putative synapomorphy for the genus, as well as the occurrence of globular and elongated glandular trichomes, isobilateral mesophyll, hypostomatic leaves, and the occurrence of cystoliths.

Genome-wide characterization of B-box gene family in Artemisia annua L. and its potential role in the regulation of artemisinin biosynthesis

Artemisinin is a sesquiterpene lactone synthesized by the Chinese medicinal plant Artemisia annua L., and is the principal component used for the treatment of malaria. Recent studies have demonstrated the potential role of B-box (BBX) transcription factors in regulating plant secondary metabolism. However, the roles and functions of BBX members in the biosynthesis of artemisinin in A. annua have not been reported yet. In this study, a total of 27 BBX members (AaBBXs) were identified and classified into five sub-groups (I-V). The AaBBXs in each sub-group shared similar gene structures, conserved domains and motifs. Additionally, multiple cis-acting elements which are responsible for light, hormones, and stress signals were found in the promoter regions of AaBBX members. Based on transcriptome data, 27 AaBBXs showed constitutive expression in different organs/tissues, while several BBX genes exhibited higher expression levels in glandular secretory trichomes (GSTs), the site of artemisinin biosynthesis. To explore the roles of AaBBX members in regulating the artemisinin biosynthesis, 7 AaBBXs (AaBBX5/6/8/15/22/23/24) were selected for further investigation. The expressions of all 7 selected AaBBXs were strongly induced by MeJA and ABA, and they were all found to be nuclear localized. Additionally, all seven proteins were found to have the ability to physically interact with AaJAZ8 in vitro. Dual-luciferase assays revealed that AaBBX5/6/8/15/22/23 can activate the promoter activity of the artemisinin biosynthetic pathway genes such as AaADS, AaCYP71AV1, AaDBR2 and AaALDH1 at different degrees. AaBBX22 showed highest expression level in A. annua GSTs, and can significantly activate the promoters of all four artemisinin biosynthetic pathway genes. Furthermore, transgenic assay results indicated that AaBBX22 acted as a positive regulator for the biosynthesis of artemisinin in A. annua. Taken together, this study provided a comprehensive genome-wide characterization of the BBX family and identified several significant BBX genes, including AaBBX22, which paves the way for further investigation into the regulatory role of the BBX gene family in artemisinin biosynthesis.