Volatile Organic Compound Composition and Glandular Trichome Characteristics of In Vitro Propagated Clinopodium pulegium (Rochel) Bräuchler: Effect of Carbon Source

Clinopodium pulegium (Rochel) Bräuchler (Lamiaceae) is an endangered species endemic to the Southern Carpathians. It is characterized by the production of high amounts of essential oils, which emit volatile organic compounds (VOCs) that have an essential role in biotic and abiotic stress responses and in plant–plant and plant–insect interactions. The present study was initiated to phytochemically examine the influence of different carbon sources in the nutrition medium on VOC emissions of micropropagated C. pulegium plants, using gas chromatography–mass spectrometry analysis of headspace VOCs. The volatile profiles were subjected to multivariate analysis with respect to the presence, concentration and type of carbon source in the nutrient medium. In addition, the effect of different carbohydrates on the density and size of the leaf glandular trichomes, the main structures involved in the emission of VOCs, was determined. A total of 19 VOCs, primarily belonging to mono- and sesquiterpenes previously described in plants, were tentatively identified. Six VOCs were produced at levels higher than 2% of the total VOC emission, dominated by pulegone, ß-pinene and menthone. Inclusion of the carbohydrates in the culture media affected the production of the main leaf trichome-associated volatile allelochemicals although the qualitative composition of the volatiles changed only slightly. Multivariate analysis showed that the concentration, rather than the carbohydrate type, influenced the VOC profile.

LC-MS Characterization and Biological Activities of Cuban Cultivars of Plectranthus neochilus Schltr

Plectranthus neochilus Schltr. (Lamiaceae) is a plant recently introduced in Cuba. Worldwide, it is an ethnomedicinal alternative for its use against microbial infections, but the Cuban population use the extracts to treat sleep disorders. To address this apparent incongruity, four collections (from different seasonal conditions in the year) of Cuban P. neochilus cultivars were analyzed in terms of their pharmacognostic characteristics. Three extracts using fresh and dried leaves were chemically and biologically characterized. UPLC-DAD-MS/MS analysis was performed to determine their chemical composition, while a panel of nine microorganisms was used to evaluate their antimicrobial activity. Finally, cytotoxic effects of different fractions were measured in three cell lines by the resazurin viability assay. In contrast to previously reported micro and macromorphological properties of P. neochilus, the leaves from the Cuban cultivars did not present glandular trichomes, nor did they produce quantifiable levels of essential oils. Moreover, aqueous extracts used by the population revealed no significant antimicrobial activity and were not cytotoxic. The three extracts showed a similar phytochemical composition, i.e., eight flavonoids, seven abietane diterpenes, and rosmarinic acid as the major constituent, most of them reported for the first time in this species. The low yield of essential oil, the absence of glandular trichomes, compounds with a high level of oxidation, and a moderate antimicrobial activity detected were the most distinctive pharmacognostic and biological characteristics of P. neochilus grown in Cuba. These aspects could explain its non-use as an antimicrobial.

Micromorphology of endemic Centaurea glaberrima subsp. divergens (Asteraceae)

In this study, the micromorphology of the vegetative and reproductive structures of the endemic Centaurea glaberrima Tausch subsp. divergens (Vis.) Hayek (Asteraceae), using scanning electron microscope (SEM), is presented for the first time. Uniseriate whip-like non-glandular and biseriate glandular trichomes are found on the surface of all aboveground parts (stem, leaves, peduncles, involucral bract). On the adaxial leaf epidermis ribbed thickenings (striation pattern) of outer periclinal cell walls, slightly curved anticlinal cell walls and anomocytic stomata are noticed. Rugose abaxial surface with thorny protuberances of the involucral bract is documented. Corolla is glabrous with longitudinally parallel epidermal cells with distinct straight outline. Isopolar, radially symmetric and tricolporate microechinate pollen grains are seen. Short stylar hairs, without cuticular striations, are present along the outer sides of the style, while the inner sides (abaxial surface) constitute the papillate stigmatic surface. Microcharacters found in cypsela are as follows: slightly ribbed body; rotund base; lateral and concave insertion; short, unicellular curly acute trichomes; smooth epidermis; fine-sulcate ornamentation; rod shaped epidermal cells with short, obtuse end walls and straight anticlinal walls; poorly developed minutely dentate pericarp rim; and dimorphic pappus with bristles of different length and morphology, with pinnules restricted to the margins of the bristles. The results obtained contribute to knowledge about the micromorphology of the studied endemic species and provide features for its better identification. The taxonomic significance of the analyzed characters is discussed. Some well defined microcharacters of the studied species might have taxonomic value

The number of glandular trichomes on the peduncles of true lavender inflorescences as an additional breeding trait for essential oil

The main receptacle of essential oil in true lavender is the peltate glandular trichomes of the calyxes in the whorls of the inflorescences. Their average size is 175 ± 25 µm, in some cases – up to 250 µm. For the extraction of lavender oil, not only the calyxes are used, but the whole inflorescences including the flowering shoots. The surface of the peduncles of lavender inflorescences is also covered with peltate glandular trichomes. However, their contribution to the total volume of essential oil in the inflorescence has almost never been determined. The aim of this research was to study the distribution density of glandular trichomes within the inflorescence and to determine the proportion of the contribution of flowering trichomes to the formation of essential oil in the inflorescence. The research was carried out in 2021 on the basis of the V.S. Pustovoit All-Russian Research Institute of Oil Crops in two ecological and geographical points of the Krasnodar region. The object of the study was the true lavender varieties Voznesenskaya 34, Rannyaya, Yuzhanka and Voznesenskaya Aroma. It was found that the size of glandular trichomes on peduncles of true lavender is 90 ± 15 µm. Their number on peduncles, depending on the variety, varies from 2141 to 3003 pcs. The density of distribution of glandular trichomes on the surface of peduncles is equal to 8.60–14.93 pcs/mm3 . The total volume of essential oil in all glandular trichomes of peduncles is 0.41–0.57 cmm . The total volume of essential oil in the inflorescences varied from 2.28 to 5.15 cmm . The share of essential oil in the glandular trichomes of the peduncles in relation to the entire inflorescence ranged from 9.33 to 19.56%. It is concluded that peltate glandular trichomes on flower-bearing axes make a significant contribution to the essential oil content of lavender inflorescences. For the selection of true lavender to increase the essential oil content and the yield of essential oil, an additional selection trait is proposed – the amount of glandular trichomes on the surface of peduncles, which can be regulated by changing their distribution density on the surface of peduncles, or increasing the length of inflorescences.

Epidermis-Specific Metabolic Engineering of Sesquiterpene Formation in Tomato Affects the Performance of Potato Aphid Macrosiphum euphorbiae

Tomato produces a number of terpenes in their glandular trichomes that contribute to host plant resistance against pests. While glandular trichomes of cultivated tomato Solanum lycopersicum primarily accumulate a blend of monoterpenes, those of the wild tomato species Solanum habrochaites produce various sesquiterpenes. Recently, we have identified two groups of sesquiterpenes in S. habrochaites accessions that negatively affect the performance and choice behavior of the potato aphid (Macrosiphum euphorbiae). Aphids are piercing-sucking herbivores that use their mouthpart to penetrate and probe plant tissues in order to ultimately access vascular tissue and ingest phloem sap. Because secondary metabolites produced in glandular trichomes can affect the initial steps of the aphid feeding behavior, introducing the formation of defensive terpenes into additional plant tissues via metabolic engineering has the potential to reduce tissue penetration by aphids and in consequence virus transmission. Here, we have developed two multicistronic expression constructs based on the two sesquiterpene traits with activity toward M. euphorbiae previously identified in S. habrochaites. Both constructs are composed of sequences encoding a prenyl transferase and a respective S. habrochaites terpene synthase, as well as enhanced green fluorescent protein as a visible marker. All three coding sequences were linked by short nucleotide sequences encoding the foot-and-mouth disease virus 2A self-processing oligopeptide which allows their co-expression under the control of one promoter. Transient expression of both constructs under the epidermis-specific Arabidopsis CER5-promoter in tomato leaves demonstrated that formation of the two sets of defensive sesquiterpenes, β-caryophyllene/α-humulene and (−)-endo-α-bergamotene/(+)-α-santalene/(+)-endo-β-bergamotene, can be introduced into new tissues in tomato. The epidermis-specific transgene expression and terpene formation were verified by fluorescence microscopy and tissue fractionation with subsequent analysis of terpene profiles, respectively. In addition, the longevity and fecundity of M. euphorbiae feeding on these engineered tomato leaves were significantly reduced, demonstrating the efficacy of this novel aphid control strategy.

Hairiness Gene Regulated Multicellular, Non-Glandular Trichome Formation in Pepper Species

Trichomes are unicellular or multicellular epidermal structures that play a defensive role against environmental stresses. Although unicellular trichomes have been extensively studied as a mechanistic model, the genes involved in multicellular trichome formation are not well understood. In this study, we first classified the trichome morphology structures in Capsicum species using 280 diverse peppers. We cloned a key gene (Hairiness) on chromosome 10, which mainly controlled the formation of multicellular non-glandular trichomes (types II, III, and V). Hairiness encodes a Cys2-His2 zinc-finger protein, and virus-induced gene silencing of the gene resulted in a hairless phenotype. Differential expression of Hairiness between the hairiness and hairless lines was due to variations in promoter sequences. Transgenic experiments verified the hypothesis that the promoter of Hairiness in the hairless line had extremely low activity causing a hairless phenotype. Hair controlled the formation of type I glandular trichomes in tomatoes, which was due to nucleotide differences. Taken together, our findings suggest that the regulation of multicellular trichome formation might have similar pathways, but the gene could perform slightly different functions in crops.

The Morphological and Anatomical Studies of The Aerial Parts of Abroma augusta L. from Semarang

Abroma augusta L. known as Devil’s cotton belongs to Malvaceae. The exploratory study aimed to study the morphological and anatomical characteristics of the aerial parts of A. augusta L. from Semarang. The transverse section of the aerial parts was made by a simple method (fresh preparation) and then observed under a binocular microscope with an optilab. All characteristics were observed and then compared with the references. The collected data were analyzed descriptively and quantitatively. In summary, the results showed that A. augusta L. was an evergreen shrub (small tree) with orthotropic and plagiotropic branches and polymorphous leaves. The inflorenscence was found in the terminal and axillar plagiotropic branching with bisex, actinomorphic, and pentamerous flowers. The fruit was unique (obconical capsule with a rounded base and truncate-tip with 5 angled wings) including cotton fibers and numerous black seeds. The petiole was composed of epidermis, collenchyma, cortical parenchyma, sclerenchyma, vascular bundle, mucilaginous ducts, and pith. The dorsiventral leaf was composed of upper and lower epidermis, palisade, and spongy parenchyma. The stomata type was ranunculaceous (anomocytic) while the guard cell was kidney-shaped. The stomata density on the abaxial leaf was higher than that of the adaxial leaf. The stellate and unicellular non-glandular trichomes, and capitate glandular trichomes were found abundantly on the petiole and leaf blade. These morphological and anatomical studies are important to support the identification as a part of the conservation effort of the plant. Further studies are recommended to investigate the root morphology and anatomy and also biochemical characteristics of each part of the plant in order to obtain complete plant identification.

A new species and taxonomic notes on Lycianthes series Glanduliferae (Solanaceae) from the Brazilian Amazon

During our analyses of Lycianthes exsiccates, as part of the taxonomic treatment for the Brazilian flora, a new species was discovered and is described and illustrated here. The species is compared and contextualized within the infra-generic classification of Lycianthes. Analyses of indument and trichomes were performed by stereomicroscopy (SM) and scanning electron microscopy (SEM). The new species, Lycianthes amazonica, is recognized as an endemic species to the Brazilian Amazon, which has its habitat described as secondary formations (capoeira) of terra-firme forests. It is closely related to L. sprucei, with which shares the scandent or vine habit, flexuous branches and ferrugineous indument of glandular trichomes. However, they are distinguished by several morphological features, including trichomes morphology, a sessile inflorescence and calyx appendages of equal length; both species belong to Lycianthes. subg. Polymeris sect. Eulycianthes ser. Glanduliferae. The description of this species expands the total number of Lycianthes species to the Brazilian Amazon to six, as well as thirteen to Brazil. The affinities of Lycianthes amazonica with its related species, distribution, ecology, and conservation status are discussed. Additionally, a lectotypification of Lycianthes sprucei, a species closely related to L. amazonica, is proposed.