Influence of light intensity on glandular trichome density, gene expression and essential oil of menthol mint (Mentha arvensisL.)

Depolymerized carrageenan expresses elicitor-like activity on Mentha arvensis L. under arsenic stress: Insights into arsenic resilience and monoterpene synthesis

Heavy metals contaminate agricultural land by limiting the productivity of crops and making them or their products unfit for consumption. Arsenic (As) is a potentially hazardous metalloid that severely impacts plants' survival. Menthol mint (Mentha arvensis L.) bears volatile compounds that are harshly exaggerated by diverse environmental factors like drought, salinity, heavy metal, temperature, photoperiod, and luminosity stresses. In this study, the phytotoxicity of As was examined in M. arvensis L. and its alleviation through the supplementation of oligomers of carrageenan. Noticeably, scanty information is available regarding the effect of irradiated carrageenan (ICA) on As-stressed plants. In order to observe the same in the case of M. arvensis L., the effect of ICA on As-treated plants was explored. The ICA concentration (foliar-applied) selected for the study was 80 mg L-1, 100 mg L-1 and 120 mg L-1, and that of As (soil-applied) was 80 mg kg-1 soil. Excess accumulation of As resulted in reduced growth, enzymatic activities, and yield and quality parameters of M. arvensis L. under As toxicity. However, the foliage application of ICA strengthens the antioxidant machinery and other physiological and oxidative stress biomarkers of the plant by facilitating the activity of superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and proline, and, therefore aids in alleviating the toxicity generated by As. Nevertheless, ICA supplementation proves beneficial in enhancing the monoterpene synthesis (essential oil production and its active constituents) of M. arvensis L. by maintaining a steady-state equilibrium between reactive oxygen species (ROS) production and its scavenging process.

Glandular trichome development, morphology, and maturation are influenced by plant age and genotype in high THC-containing cannabis (Cannabis sativa L.) inflorescences

BACKGROUND

Glandular capitate trichomes which form on bract tissues of female inflorescences of high THC-containing Cannabis sativa L. plants are important sources of terpenes and cannabinoids. The influence of plant age and cannabis genotype on capitate trichome development, morphology, and maturation has not been extensively studied. Knowledge of the various developmental changes that occur in trichomes over time and the influence of genotype and plant age on distribution, numbers, and morphological features should lead to a better understanding of cannabis quality and consistency.

METHODS

Bract tissues of two genotypes-"Moby Dick" and "Space Queen"-were examined from 3 weeks to 8 weeks of flower development using light and scanning electron microscopy. Numbers of capitate trichomes on upper and lower bract surfaces were recorded at different positions within the inflorescence. Observations on distribution, extent of stalk formation, glandular head diameter, production of resin, and extent of dehiscence and senescence were made at various time points. The effects of post-harvesting handling and drying on trichome morphology were examined in an additional five genotypes.

RESULTS

Two glandular trichome types-bulbous and capitate (sessile or stalked)-were observed. Capitate trichome numbers and stalk length were significantly (P = 0.05) greater in "Space Queen" compared to "Moby Dick" at 3 and 6 weeks of flower development. Significantly more stalked-capitate trichomes were present on lower compared to upper bract surfaces at 6 weeks in both genotypes, while sessile-capitate trichomes predominated at 3 weeks. Epidermal and hypodermal cells elongated to different extents during stalk formation, producing significant variation in length (from 20 to 1100 μm). Glandular heads ranged from 40 to 110 μm in diameter. Maturation of stalked-capitate glandular heads was accompanied by a brown color development, reduced UV autofluorescence, and head senescence and dehiscence. Secreted resinous material from glandular heads appeared as droplets on the cuticular surface that caused many heads to stick together or collapse. Trichome morphology was affected by the drying process.

CONCLUSION

Capitate trichome numbers, development, and degree of maturation were influenced by cannabis genotype and plant age. The observations of trichome development indicate that asynchronous formation leads to different stages of trichome maturity on bracts. Trichome stalk lengths also varied between the two genotypes selected for study as well as over time. The variability in developmental stage and maturation between genotypes can potentially lead to variation in total cannabinoid levels in final product. Post-harvest handling and drying were shown to affect trichome morphology.

Successive harvests affect the aromatic and polyphenol profiles of novel catnip (Nepeta cataria L.) cultivars in a genotype-dependent manner

INTRODUCTION

Catnip (Nepeta cataria L.) produces volatile iridoid terpenes, mainly nepetalactones, with strong repellent activity against species of arthropods with commercial and medical importance. Recently, new catnip cultivars CR3 and CR9 have been developed, both characterized by producing copious amounts of nepetalactones. Due to its perennial nature, multiple harvests can be obtained from this specialty crop and the effects of such practice on the phytochemical profile of the plants are not extensively studied.

METHODS

In this study we assessed the productivity of biomass, chemical composition of the essential oil and polyphenol accumulation of new catnip cultivars CR3 and CR9 and their hybrid, CR9×CR3, across four successive harvests. The essential oil was obtained by hydrodistillation and the chemical composition was obtained via gas chromatography-mass spectrometry (GC-MS). Individual polyphenols were quantified by Ultra-High-Performance Liquid Chromatography- diode-array detection (UHPLC-DAD).

RESULTS

Although the effects on biomass accumulation were independent of genotypes, the aromatic profile and the accumulation of polyphenols had a genotype-dependent response to successive harvests. While cultivar CR3 had its essential oil dominated by E,Z-nepetalactone in all four harvests, cultivar CR9 showed Z,E-nepetalactone as the main component of its aromatic profile during the 1^st, 3^rd and 4^th harvests. At the second harvest, the essential oil of CR9 was mainly composed of caryophyllene oxide and (E)-β-caryophyllene. The same sesquiterpenes represented the majority of the essential oil of the hybrid CR9×CR3 at the 1^st and 2^nd successive harvests, while Z,E-nepetalactone was the main component at the 3^rd and 4^th harvests. For CR9 and CR9×CR3, rosmarinic acid and luteolin diglucuronide were at the highest contents at the 1^st and 2^nd harvest, while for CR3 the peak occurred at the 3^rd successive harvest.

DISCUSSION

The results emphasize that agronomic practices can significantly affect the accumulation of specialized metabolites in N. cataria and the genotype-specific interactions may indicate differential ecological adaptations of each cultivar. This is the first report on the effects of successive harvest on these novel catnip genotypes and highlights their potential for the supply of natural products for the pest control and other industries.

Physiological responses and antioxidant properties of coriander plants (Coriandrum sativum L.) under different light intensities of red and blue lights

Coriander (Coriandrum sativum L.) contains abundant antioxidants and essential oils which can provide antibacterial, antifungal, and antioxidant activities in the pharmaceutical, health and food production industry. To improve the economic values of coriander, the relationships between optimal light treatments for maximizing both plant growth and the antioxidant and essential oil content of coriander leaves need to be determined. Plants were exposed to five light-emitting diodes spectral color mixtures, high blue light (BL) intensity induced the levels of reducing power response. The light treatments were then adjusted for the analysis of secondary metabolite compounds of coriander leaves. Among 30 identified compounds, the amounts of decamethyl-cyclopentasiloxane and dodecane were significantly reduced in the R80 + G50 + B50 condition, whereas dodecamethyl-cyclohexasiloxane level was significantly reduced in R50 + G50 + B80 condition. Various light quality and intensity combinations influenced the accumulations of chlorophyll and phytochemical contents, mediated antioxidative properties, and secondary metabolites of coriander leaves, which may be useful in developing a new LED lighting apparatus optimized for coriander production in plant factories.

Transcriptome Analysis of Light-Regulated Monoterpenes Biosynthesis in Leaves of Mentha canadensis L

Light is a key environmental aspect that regulates secondary metabolic synthesis. The essential oil produced in mint (Mentha canadensis L.) leaves is used widely in the aromatics industry and in medicine. Under low-light treatment, significant reductions in peltate glandular trichome densities were observed. GC-MS analysis showed dramatically reduced essential oil and menthol contents. Light affected the peltate glandular trichomes’ development and essential oil yield production. However, the underlying mechanisms of this regulation were elusive. To identify the critical genes during light-regulated changes in oil content, following a 24 h darkness treatment and a 24 h recovery light treatment, leaves were collected for transcriptome analysis. A total of 95,579 unigenes were obtained, with an average length of 754 bp. About 56.58% of the unigenes were annotated using four public protein databases: 10,977 differentially expressed genes (DEGs) were found to be involved in the light signaling pathway and monoterpene synthesis pathway. Most of the TPs showed a similar expression pattern: downregulation after darkness treatment and upregulation after the return of light. In addition, the genes involved in the light signal transduction pathway were analyzed. A series of responsive transcription factors (TFs) were identified and could be used in metabolic engineering as an effective strategy for increasing essential oil yields.

Productive, metabolic and anatomical parameters of menthol mint are influenced by light intensity

The cultivation of aromatic species to obtain essential oils has great economic importance, presenting an increasing demand from different industrial sectors, especially to menthol mint (Mentha arvensis L.) essential oil, rich in menthol (70-80%). Consortium cultivation has been an important practice in agricultural systems whose land use is necessary, consequently promoting strong competition for light in reduced space. Thus, this study aimed verifying if different light intensities might promote chemical, metabolical and anatomical alterations in menthol mint. Plants were grown in greenhouse at different average of light intensities (137, 254, 406 and 543 µmol photons m2 s1). Samples were collected 43 days after germination and submitted to following analyses: Gravimetric test, photosynthetic pigments, soluble fractions, enzymatic activity, N-total, trichome density and histochemistry and chemometric test based on essential oil chemical profile. Fresh mass gain, trichome density, essential oil content and soluble sugars were positively influenced by light intensity increase. On the other hand, total-N, NO3--N and pigments content have decreased influenced by light intensity increase. In the secretion from the trichomes, phenolic substances were reported, as well as lipophilic ones in the peltate ones. The increase of oxygenated monoterpenes was favored by light intensity decrease.

Trichome Density in Relation to Volatiles Emission and 1,8-Cineole Synthase Gene Expression in Thymus albicans Vegetative and Reproductive Organs

1,8-Cineole is the main volatile produced by Thymus albicans Hoffmanns. & Link 1,8-cineole chemotype. To understand the contribution of distinct plant organs to the high 1,8-cineole production, trichome morphology and density, as well as emitted volatiles and transcriptional expression of the 1,8-cineole synthase (CIN) gene were determined separately for T. albicans leaves, bracts, calyx, corolla and inflorescences. Scanning electron microscopy (SEM) and stereoscope microscopy observations showed the highest peltate trichome density in leaves and bracts, significantly distinct from calyx and corolla. T. albicans volatiles were collected by solid phase micro extraction (SPME) and analyzed by gas chromatography-mass spectrometry (GC/MS) and by GC for component identification and quantification, respectively. Of the 23 components identified, 1,8-cineole was the dominant volatile (57-93 %) in all T. albicans plant organs. The relative amounts of emitted volatiles clearly separated vegetative from reproductive organs. Gene expression of CIN was assigned to all organs analyzed and was consistent with the relatively high emission of 1,8-cineole in leaves and bracts. Further studies will be required to analyze monoterpenoid biosynthesis by each type of glandular trichome.

Optimization of Photosynthetic Photon Flux Density and Root-zone Temperature for Enhancing Secondary Metabolite Accumulation and Production of Coriander in Plant Factory

Coriander is an important aromatic plant, and contains abundant secondary metabolites that are considered to be beneficial for health. The demand for high-quality and fresh coriander in large cities has been growing rapidly. Plant factories are advanced indoor cultivation systems that can produce high-quality plants inside cities with a high productivity. This study aimed to maximize plant growth and the secondary metabolites production of coriander, by regulating photosynthetic photon flux density (PPFD) and root-zone temperature (RZT). Three PPFDs (100, 200, and 300 µmol m−2 s−1) and three RZTs (20, 25, and 30 °C) were applied on coriander plants grown hydroponically in a plant factory. The plant biomass and water content of leaf and stem were highest under RZT of 25 °C with a PPFD of 300 µmol m−2 s−1. However, chlorogenic acid, rutin, trans-2-decenal, total phenolic concentrations and the antioxidant capacity of the coriander plant were greatest under the combination of PPFD (300 µmol m−2 s−1) and RZT (30 °C). Chlorogenic acid in leaves responded more sensitively to PPFD and RZT than rutin. Controlling PPFD and RZT is effective in optimizing the yield and quality of coriander plants. The findings are expected to be applied to commercial plant production in plant factories.

The ratio of trichomes to stomata is associated with water use efficiency in Solanum lycopersicum (tomato)

Trichomes are specialised structures that originate from the aerial epidermis of plants, and play key roles in the interaction between the plant and the environment. In this study we investigated the trichome phenotypes of four lines selected from the Solanum lycopersicum × Solanum pennellii introgression line (IL) population for differences in trichome density, and their impact on plant performance under water-deficit conditions. We performed comparative analyses at morphological and photosynthetic levels of plants grown under well-watered (WW) and also under water-deficit (WD) conditions in the field. Under WD conditions, we observed higher trichome density in ILs 11-3 and 4-1, and lower stomatal size in IL 4-1 compared with plants grown under WW conditions. The intrinsic water use efficiency (WUEi ) was higher under WD conditions in IL 11-3, and the plant-level water use efficiency (WUEb ) was also higher in IL 11-3 and in M82 for WD plants. The ratio of trichomes to stomata (T/S) was positively correlated with WUEi and WUEb , indicating an important role for both trichomes and stomata in drought tolerance in tomato, and offering a promising way to select for improved water use efficiency of major crops.