The Morphoregulatory Role of Thidiazuron: Metabolomics-Guided Hypothesis Generation for Mechanisms of Activity

Genetic modification of Water spinach (Ipomoea aquatica), a genoprotective perennial leafy green

Improvement of leafy greens, especially perennials with year-round harvesting, is binding to the food security drive. "Food for All" by WHO demands the improvement of regional crops due to the agroclimatic specificity to ensure regional food security. Water spinach (Ipomoea aquatica) is a perennial nutritious leafy green with regional/ethnic cultivation. We accomplished organogenesis and somatic embryogenesis from different explants of I. aquatica, and transgenesis and genome editing through Agrobacterium-mediated transformation. The Ipomoea Basal (CLC-CP) medium was superior to the Murashige and Skoog medium. Hypocotyl explants produced a mean of 12.4 shoots on CLC-CP containing 4.5 μM thidiazuron and 8.7 μM gibberellic acid (GA3), 50 mg l-1 ascorbic acid (AA), and 100 mg l-1 adenine hemi-sulfate (AdS). Leaf and root explants induced the highest somatic embryos on a medium containing AdS, AA, 4.4/4.7 μM 6-benzyladenine/kinetin (KIN), and 0.45 μM 2,4-dichlorophenoxyacetic acid. CLC-CP medium with 4.7 μM KIN, 8.7 μM GA3, AA, and AdS exhibited elongation of hypocotyl-derived shoots and maturation of somatic embryos. A. tumefaciens-mediated transformation of hypocotyl developed a mean of 3.7 GFP expressing shoots per explant; leaf and root produced 4.3 and 3.1 somatic embryos, respectively. A. rhizogenes infection induced a mean of 4.1 and 3.4 hairy roots from leaf and root explants, respectively. Western blotting of the GFP protein validates water spinach to express human therapeutic proteins. Genome editing of IaNAP1 using hypocotyl explants confirmed the reproducibility of transformation. The plantlets exhibited 100% survival in soil. The present protocol is useful for improving this ethnic leafy green with traits-of-interest.

Better Together: Synergistic Enhancement of AuNPs and Bifunctional Monomers in a Dual-Channel Molecularly Imprinting Electrochemical Sensor for Simultaneous Detection of Diuron and Thidiazuron

The combination of diuron (DU) and thidiazuron (TDZ) is commonly used in cotton production for its excellent adaptability to low temperatures, which may lead to increased crop and soil pollution. The simultaneous detection of DU and TDZ poses significant challenges due to their weak and overlapping signals, along with an unclear electrochemical detection mechanism for TDZ. This study developed a dual-channel multifunctional molecularly imprinted electrochemical (MMIP-EC) sensing platform by optimizing the substrate material and MIP layer for high performance. First, amino-functionalized graphene-based poly(pyrrole)-poly(3,4-ethylenedioxythiophene) (NH2-rGO/PPy-PEDOT) with high conductivity was synthesized as the substrate. Subsequently, MMIPs were prepared in one step using electropolymerization by introducing chloroauric acid (HAuCl4) and bifunctional monomers (dopamine and thiophene). This method not only enhanced specific binding capacity of the MMIP layer but also amplified the signal through the synergistic effect of reduced AuNPs and bifunctional monomers. Furthermore, two independent modules (MMIP-DU and MMIP-TDZ) were integrated into a dual-channel EC platform for simultaneous transmission of DU and TDZ responses to separate windows. Finally, based on high-performance liquid chromatography-mass spectrometry (HPLC-MS) and electrochemical kinetics studies, it was speculated that the electrochemical oxidation of TDZ via the carbonylation of a secondary amine under strongly acidic conditions, followed by hydrolysis to form a carboxyl group, reveals the electrochemical oxidation mechanism of TDZ. The developed sensor exhibited excellent performance in selectivity and sensitivity, with low detection limits of 26.6 pg/mL (DU) and 39.2 pg/mL (TDZ). In conclusion, this sensing platform presents a novel perspective for the cost-effective and highly efficient detection of diverse environmental pollutants.

Induction of microspore embryogenesis in bread wheat by mannitol pre-treatment is associated with the disruption of endogenous hormone balance and substantial accumulation of auxins

BACKGROUND

Hormonal homeostasis plays a critical role in the regulation of microspore embryogenesis (ME). The balance between endogenous phytohormones must be altered to induce microspore reprogramming from the classical pollen-formation pathway to embryogenic development, but too extensive changes may be detrimental. In the present study, the levels of auxins, cytokinins and abscisic acid were monitored in the anthers of two Polish winter wheat F1 lines and the spring cultivar Pavon highly differentiated in terms of ME effectiveness. Analyses were carried out at subsequent steps of the ME induction procedure that combined low temperature, sodium selenate and mannitol tiller pre-treatment.

RESULTS

Of all the factors tested, mannitol induced the most profound effect on phytohormones and their homeostasis in wheat anthers. It significantly increased the accumulation of all auxins and decreased the levels of most cytokinins, while the change in ABA content was limited to cv. Pavon. In an attempt to alleviate this hormonal shock, we tested several modifications of the induction medium hormonal composition and found thidiazuron to be the most promising in stimulating the embryogenic development of wheat microspores.

CONCLUSIONS

The lack of ABA-driven stress defence responses may be one of the reasons for the low effectiveness of ME induction in winter wheat microspore cultures. Low cytokinin level and a disturbed auxin/cytokinin balance may then be responsible for the morphological abnormalities observed during the next phases of embryogenic microspore development. One possible solution is to modify the hormonal composition of the induction medium with thidiazuron identified as the most promising component.

HormonomicsDB: a novel workflow for the untargeted analysis of plant growth regulators and hormones

Background

Metabolomics is the simultaneous determination of all metabolites in a system. Despite significant advances in the field, compound identification remains a challenge. Prior knowledge of the compound classes of interest can improve metabolite identification. Hormones are a small signaling molecules, which function in coordination to direct all aspects of development, function and reproduction in living systems and which also pose challenges as environmental contaminants. Hormones are inherently present at low levels in tissues, stored in many forms and mobilized rapidly in response to a stimulus making them difficult to measure, identify and quantify.

Methods

An in-depth literature review was performed for known hormones, their precursors, metabolites and conjugates in plants to generate the database and an RShiny App developed to enable web-based searches against the database. An accompanying liquid chromatography - mass spectrometry (LC-MS) protocol was developed with retention time prediction in Retip. A meta-analysis of 14 plant metabolomics studies was used for validation.

Results

We developed HormonomicsDB, a tool which can be used to query an untargeted mass spectrometry (MS) dataset against a database of more than 200 known hormones, their precursors and metabolites. The protocol encompasses sample preparation, analysis, data processing and hormone annotation and is designed to minimize degradation of labile hormones. The plant system is used a model to illustrate the workflow and data acquisition and interpretation. Analytical conditions were standardized to a 30 min analysis time using a common solvent system to allow for easy transfer by a researcher with basic knowledge of MS. Incorporation of synthetic biotransformations enables prediction of novel metabolites.

Conclusions

HormonomicsDB is suitable for use on any LC-MS based system with compatible column and buffer system, enables the characterization of the known hormonome across a diversity of samples, and hypothesis generation to reveal knew insights into hormone signaling networks.

Antibacterial Activity and Untargeted Metabolomics Profiling of Acalypha arvensis Poepp

The search for potent antimicrobial compounds is critical in the face of growing antibiotic resistance. This study explores Acalypha arvensis Poepp. (A. arvensis), a Caribbean plant traditionally used for disease treatment. The dried plant powder was subjected to successive extractions using different solvents: hexane (F1), dichloromethane (F2), methanol (F3), a 50:50 mixture of methanol and water (F4), and water (F5). Additionally, a parallel extraction was conducted using a 50:50 mixture of methanol and chloroform (F6). All the fractions were evaluated for their antimicrobial activity, and the F6 fraction was characterized using untargeted metabolomics using SPME-GC×GC-TOFMS. The extracts of A. arvensis F3, F4, and F5 showed antibacterial activity against Staphylococcus aureus ATCC 25923 (5 mg/mL), MRSA BA22038 (5 mg/mL), and Pseudomonas aeruginosa ATCC 27853 (10 mg/mL), and fraction F6 showed antibacterial activity against Staphylococcus aureus ATCC 29213 (2 mg/mL), Escherichia coli ATCC 25922 (20 mg/mL), Pseudomonas aeruginosa ATCC 27853 (10 mg/mL), Enterococcus faecalis ATCC 29212 (10 mg/mL), Staphylococcus aureus 024 (2 mg/mL), and Staphylococcus aureus 003 (2 mg/mL). Metabolomic analysis of F6 revealed 2861 peaks with 58 identified compounds through SPME and 3654 peaks with 29 identified compounds through derivatization. The compounds included methyl ester fatty acids, ethyl ester fatty acids, terpenes, ketones, sugars, amino acids, and fatty acids. This study represents the first exploration of A. arvensis metabolomics and its antimicrobial potential, providing valuable insights for plant classification, phytochemical research, and drug discovery.

Indirect regeneration in Ficus lyrata Warb. and metabolite profiles influenced by nitric oxide and Plant growth regulators

BACKGROUND

To establish an indirect regeneration protocol in Ficus lyrata, a three-phase experiment (callus induction, morphogenic callus induction, and plant regeneration) based on auxin, cytokinin, and nitric oxide interactions was designed and implemented using leaf explants. The metabolite profiles (amino acid profile, total phenolic content, total soluble sugars, and total antioxidant activity) alteration patterns were also investigated to determine the metabolites contributing to the progress of each phase.

RESULTS

Results demonstrated that 11 out of 48 implemented treatments resulted in morphogenic callus induction (morphogenic treatments), and nitric oxide played a key role in increasing efficiency from 13 to 100%. More importantly, nitric oxide cross-talk with cytokinins was necessary for shoot regeneration from morphogenic calli. Only 4 out of all 48 implemented treatments were capable of shoot regeneration (regenerative treatments), and among them, PR42 treatment led to the highest shoot regeneration rate (86%) and maximum mean number of shoot/explant (10.46). Metabolite analyses revealed that the morphogenic and regenerative treatments followed similar metabolite alterations, which were associated with increased biosynthesis of arginine, lysine, methionine, asparagine, glutamine, histidine, threonine, leucine, glycine, serine amino acids, total soluble sugars content, and total antioxidant activity. On the contrary, non-morphogenic and non-regenerative treatments caused the accumulation of a significantly greater total phenolic content and malondialdehyde in the explant cells, which reflexed the stressful condition of the explants.

CONCLUSIONS

It could be concluded that the proper interactions of auxin, cytokinins, and nitric oxide could result in metabolite biosynthesis alterations, leading to triggering cell proliferation, morphogenic center formation, and shoot regeneration.

Evaluation of the yield, chemical composition and biological properties of essential oil from bioreactor-grown cultures of Salvia apiana microshoots

Microshoot cultures of the North American endemic Salvia apiana were established for the first time and evaluated for essential oil production. Stationary cultures, grown on Schenk-Hildebrandt (SH) medium, supplemented with 0.22 mg/L thidiazuron (TDZ), 2.0 mg/L 6-benzylaminopurine and 3.0% (w/v) sucrose, accumulated 1.27% (v/m dry weight) essential oil, consisting mostly of 1,8-cineole, β-pinene, α-pinene, β-myrcene and camphor. The microshoots were adapted to agitated culture, showing biomass yields up to ca. 19 g/L. Scale-up studies demonstrated that S. spiana microshoots grow well in temporary immersion systems (TIS). In the RITA bioreactor, up to 19.27 g/L dry biomass was obtained, containing 1.1% oil with up to ca. 42% cineole content. The other systems employed, i.e. Plantform (TIS) and a custom made spray bioreactor (SGB), yielded ca. 18 and 19 g/L dry weight, respectively. The essential oil content of Plantform and SGB-grown microshoots was comparable to RITA bioreactor, however, the content of cineole was substantially higher (ca. 55%). Oil samples isolated from in vitro material proved to be active in acetylcholinesterase (up to 60.0% inhibition recorded for Plantform-grown microshoots), as well as hyaluronidase and tyrosinase-inhibitory assays (up to 45.8 and 64.5% inhibition observed in the case of the SGB culture).

The multipotent thidiazuron: A mechanistic overview of its roles in callogenesis and other plant cultures in vitro

Thidiazuron (TDZ) is an active substituted phenyl urea compound that has found a significant role as a plant growth regulator. The most exciting aspect of its function is that it can mimic auxins and cytokinin but is chemically different from these two. Many theories have been put forward, and experiments performed to understand the mode of action of TDZ in callogenesis. One suggested mechanism presents that it works by inhibiting the cytokinin degrading enzymes that compete with cytokinin for an active site on the enzyme. An example is the TDZ-induced suppressed expression of gibberellic acid (GA) biosynthesis genes encoding GA3 and GA20 oxidases. This is entailed with a slightly increased expression of GA catabolism genes encoding GA20 oxidase. Similarly, one of the recommendations is that TDZ induces the expression of specific genes and transcription regulatory sequences that are either responsible directly for callus formation or in turn induce other auxins or cytokinin for callogenesis. There is no concise review available that discusses the details of TDZ-induced callus, specifically and other in vitro cultures in general. This review is an attempt to explore all these pathways and mechanisms involved in callogenesis in plants stimulated by TDZ.

Thidiazuron: New Trends and Future Perspectives to Fight Xylella fastidiosa in Olive Trees

These days, most of our attention has been focused on the COVID-19 pandemic, and we have often neglected what is happening in the environment. For instance, the bacterium Xylella fastidiosa re-emerged as a plant pathogen of global importance in 2013 when it was first associated with an olive tree disease epidemic in Italy, called Olive Quick Decline Syndrome (OQDS), specifically caused by X. fastidiosa subspecies pauca ST53, which affects the Salento olive trees (Apulia, South-East Italy). This bacterium, transmitted by the insect Philaenus spumarius, is negatively reshaping the Salento landscape and has had a very high impact in the production of olives, leading to an increase of olive oil prices, thus new studies to curb this bacterium are urgently needed. Thidiazuron (TDZ), a diphenylurea (N-phenyl-1,2,3-thiadiazol-5-yl urea), has gained considerable attention in recent decades due to its efficient role in plant cell and tissue culture, being the most suitable growth regulator for rapid and effective plant production in vitro. Its biological activity against bacteria, fungi and biofilms has also been described, and the use of this low-cost compound to fight OQDS may be an intriguing idea.

High-frequency adventitious shoot organogenesis from in vitro stem explants of Scutellaria araxensis Grossh

The present study introduced an in vitro shoot organogenesis protocol for the medicinal plant Scutellaria araxensis (Lamiaceae). Stem, leaf, and petiole explants were cultured in half-strength Murashige and Skoog (MS) medium containing different concentrations of 6-benzylaminopurine (BAP) alone or in combination with thidiazuron (TDZ), indole-3-butyric acid (IBA), or α-naphthalene acetic acid. Callus formation occurred from stem and petiole explants in most cultures; however, in leaf explants, it was observed only in cultures containing 0.5 mg/l BAP supplemented with TDZ at all concentrations. The highest frequency of indirect shoot induction (100 and 90%) with an average of 20.33 and 12 shoots per explant was observed in stem-derived calli cultured on half-strength MS medium containing 2.0 mg/l BAP plus 0.5 and 1.5 mg/l TDZ, respectively. The best direct shoot organogenesis (40%) was observed in stem explants cultured on half-strength MS medium containing 0.5 mg/l BAP and 0.5 mg/l IBA with a mean of 18 shoots per stem explant. The regenerated micro-shoots were elongated on a medium fortified with 0.5 mg/l gibberellic acid and then successfully rooted in half-strength MS medium supplemented with 0.5 mg/l IBA. The obtained plantlets were acclimatized in a growth chamber with a survival rate of 100%. This study is the first report of a simple and efficient in vitro shoot organogenesis and regeneration protocol for S. araxensis by using stem explants, which could be useful for the conservation, genetic manipulation, and exploitation of biological molecules of this valuable genetic source.

Accelerating gametophytic growth in the model hornwort Anthoceros agrestis

PREMISE

Hornworts belong to a unique lineage of bryophytes with critical traits for elucidating the evolution of land plants; however, the development of functional genetic tools for hornworts has been hampered by their relatively slow gametophytic growth.

METHODS

To identify the external factors that influence the development of hornwort gametophytes and potentially augment their growth, we evaluated the contributions of several culture medium components on the axenic gametophytic growth of Anthoceros agrestis, a model hornwort. A streamlined growth assay utilizing semiautomated image analysis was developed to rapidly quantify and compare tissue development spanning four weeks of culture on solidified medium.

RESULTS

The addition of sucrose, ammonium nitrate, activated charcoal, pH buffering, and growth regulators (2,4-dichlorophenoxyacetic acid, 6-benzylaminopurine, and thidiazuron) affected gametophyte tissue survival, growth patterns, and the rate of thalli growth. Subsequently, an optimized medium composition and growth regimen for accelerating A. agrestis gametophytic growth were formulated, which at four weeks of culture increased the tissue wet weight by 2.1- to 8.5-fold compared with other previously utilized hornwort growth media.

DISCUSSION

Our protocol for generating vigorous starting material and accelerated tissue regeneration is pertinent for advancing gene function characterization and genome editing in hornworts.

Micropropagation of Feverfew (Tanacetum parthenium) and Quantification of Parthenolide Content in Its Micropropagated and Conventionally Grown Plants

Feverfew (Tanacetum parthenium) is a well-known multi-functional plant with anti-inflammatory, cardiotonic, antiangiogenic, and anticancer effects. The therapeutic value of this plant is due to its phytochemical constitutes, especially parthenolide. Tissue culture techniques have been applied to improve the bioactive components of many herbal plants. Hence, this study, was carried out to establish a protocol for micropropagation of the feverfew plant and to quantify parthenolide content in its micropropagated and conventionally grown plants. To establish an aseptic culture, different concentrations of sodium hypochlorite (NaOCl) were investigated for seed surface sterilization. Besides, the effects of plant growth regulators (PGRs) on the callus induction, shoot organogenesis from callus and in vitro rooting were evaluated. Additionally, the parthenolide yield of the micropropagated and conventionally grown plants was determined by using high-performance liquid chromatography (HPLC). The results showed that surface sterilization of feverfew seeds with 6% NaOCl for 15 min obtained 65.00 ± 2.69% aseptic seeds. Murashige and Skoog (MS) medium supplemented with 0.4 mg/L thidiazuron (TDZ) and 2 mg/L 2,4-dichlorophenoxy acetic acid (2,4-D) resulted in 86.00 ± 1.72% callus induction. The highest number of shoots (5.00 ± 0.15) per explant was obtained in the treatment of MS medium supplemented with 5 mg/L zeatin. MS medium fortified with 3 mg/L indole-3-butyric acid (IBA) produced the maximum number of roots per plantlet (8.90 ± 0.35). A total of 90% of the micropropagated plantlets survived when planted in perlite + peat moss (1:1 v/v); the micropropagated plantlets were successfully established in the ex vitro conditions. According to parthenolide analysis, its level was significantly higher in the micropropagated plants than conventionally grown plants. Among different solvents, ethanolic extraction obtained the highest parthenolide content of the feverfew plant. Hence, it can be concluded that micropropagation of feverfew could be applied to produce disease-free planting materials and to improve the parthenolide content of the feverfew plant.

A Systematic Review of Melatonin in Plants: An Example of Evolution of Literature

Melatonin (N-acetyl-5-methoxy-tryptamine) is a mammalian neurohormone, antioxidant and signaling molecule that was first discovered in plants in 1995. The first studies investigated plant melatonin from a human perspective quantifying melatonin in foods and medicinal plants and questioning whether its presence could explain the activity of some plants as medicines. Starting with these first handful of studies in the late 1990s, plant melatonin research has blossomed into a vibrant and active area of investigation and melatonin has been found to play critical roles in mediating plant responses and development at every stage of the plant life cycle from pollen and embryo development through seed germination, vegetative growth and stress response. Here we have utilized a systematic approach in accordance with the preferred reporting items for systematic reviews and meta-analyses (PRISMA) protocols to reduce bias in our assessment of the literature and provide an overview of the current state of melatonin research in plants, covering 1995-2021. This review provides an overview of the biosynthesis and metabolism of melatonin as well as identifying key themes including: abiotic stress responses, root development, light responses, interkingdom communication, phytohormone and plant signaling. Additionally, potential biases in the literature are investigated and a birefringence in the literature between researchers from plant and medical based which has helped to shape the current state of melatonin research. Several exciting new opportunities for future areas of melatonin research are also identified including investigation of non-crop and non-medicinal species as well as characterization of melatonin signaling networks in plants.