Study of cis-cinnamic acid in Arabidopsis thaliana

Isolation and identification of allelochemicals and their activities and functions

Allelopathy is the interaction between donor plants and receiver plants through allelochemicals. According to a great number of publications, allelopathy may be involved in several ecological aspects such as the formation of monospecific stands and sparse understory vegetation for certain plant species. Allelopathy also contributes to the naturalization of invasive plant species in introduced ranges. Autotoxicity is a particular type of allelopathy involving certain compounds. Many medicinal plants have been reported to show relatively high allelopathic activity. We selected plant species that show high allelopathic activity and isolated allelochemicals through the bioassay-guided purification process. More than 100 allelochemicals, including novel compounds have been identified in some medicinal and invasive plants, plants forming monospecific stands, plants with sparse understory vegetation, and plants showing autotoxicity. The allelopathic activity of benzoxazinones and related compounds was also determined.

Metabolic diversity shapes vegetation-enhanced methane oxidation in landfill covers: Multi-omics study of rhizosphere microorganisms

Vegetation root exudates have the ability to shape soil microbial community structures, thereby enhancing CH4 bio-oxidation capacity in landfill cover systems. In this study, the CH4 oxidation capacity of indigenous vegetation rhizosphere microorganisms within operational landfill covers in Chongqing, China, was investigated for the first time, with the objective of identifying suitable plant candidates for CH4 mitigation initiatives within landfill cover systems. Furthermore, a multi-omics methodology was employed to explore microbial community structures and metabolic variances within the rhizospheric environment of diverse vegetation types. The primary aim was to elucidate the fundamental factors contributing to divergent CH4 oxidation capacities observed in rhizosphere soils. The findings demonstrated that herbaceous vegetation predominated in landfill covers. Notably, Rumex acetosa exhibited the highest CH4 oxidation capacity in the rhizosphere soil, approximately 20 times greater than that in non-rhizosphere soil. Root exudates played a crucial role in inducing the colonization of CH4-oxidizing functional microorganisms in the rhizosphere, subsequently prompting the development of specific metabolic pathways. This process, in turn, enhanced the functional activity of the microorganisms while concurrently bolstering their tolerance to microbial pollutants. Consequently, the addition of substances like Limonexic acid strengthened the CH4 bio-oxidation process, thereby underscoring the suitability of Rumex acetosa and similar vegetation species as preferred choices for landfill cover vegetation restoration.

Osmotic stress-induced lignin synthesis is regulated at multiple levels in alfalfa (Medicago sativa L.)

Alfalfa is an important forage crop. Yield and quality are frequently threatened by extreme environments such as drought and salt stress. As a component of the cell wall, lignin plays an important role in the abiotic stress response, the mechanisms of which have not been well clarified. In this study, we combined physiological, transcriptional, and metabolic analyses to reveal the changes in lignin content in alfalfa under mannitol-induced osmotic stress. Osmotic stress enhanced lignin accumulation by increasing G and S units, which was associated with increases in enzyme activities and decreases in 8 intermediate metabolites. Upon combined analysis of the transcriptome and metabolome, we identified five key structural genes and several coexpressed transcription factors, such as MYB and WRKY, which may play a core role in regulating lignin content and composition under osmotic stress. In addition, lignin synthesis was positively regulated by ABA but negatively regulated by ethylene under osmotic stress. These results provide new insight into the regulatory mechanism of lignin synthesis under abiotic stress.

Opposing effects of trans- and cis-cinnamic acid during rice coleoptile elongation

The phenylpropanoid cinnamic acid (CA) is a plant metabolite that can occur under a trans- or cis-form. In contrast to the proven bioactivity of the cis-form (c-CA), the activity of trans-CA (t-CA) is still a matter of debate. We tested both compounds using a submerged rice coleoptile assay and demonstrated that they have opposite effects on cell elongation. Notably, in the tip of rice coleoptile t-CA showed an inhibiting and c-CA a stimulating activity. By combining transcriptomics and (untargeted) metabolomics with activity assays and genetic and pharmacological experiments, we aimed to explain the underlying mechanistic processes. We propose a model in which c-CA treatment activates proton pumps and stimulates acidification of the apoplast, which in turn leads to the loosening of the cell wall, necessary for elongation. We hypothesize that c-CA also inactivates auxin efflux transporters, which might cause a local auxin accumulation in the tip of the coleoptile. For t-CA, the phenotype can partially be explained by a stimulation of cell wall polysaccharide feruloylation, leading to a more rigid cell wall. Metabolite profiling also demonstrated that salicylic acid (SA) derivatives are increased upon t-CA treatment. As SA is a known antagonist of auxin, the shift in SA homeostasis provides an additional explanation of the observed t-CA-mediated restriction on cell growth.

Piperonylic acid alters growth, mineral content accumulation and reactive oxygen species-scavenging capacity in chia seedlings

p-Coumaric acid synthesis in plants involves the conversion of phenylalanine to trans-cinnamic acid via phenylalanine ammonia-lyase (PAL), which is then hydroxylated at the para-position under the action of trans-cinnamic acid 4-hydroxylase. Alternatively, some PAL enzymes accept tyrosine as an alternative substrate and convert tyrosine directly to p-coumaric acid without the intermediary of trans-cinnamic acid. In recent years, the contrasting roles of p-coumaric acid in regulating the growth and development of plants have been well-documented. To understand the contribution of trans-cinnamic acid 4-hydroxylase activity in p-coumaric acid-mediated plant growth, mineral content accumulation and the regulation of reactive oxygen species (ROS), we investigated the effect of piperonylic acid (a trans-cinnamic acid 4-hydroxylase inhibitor) on plant growth, essential macroelements, osmolyte content, ROS-induced oxidative damage, antioxidant enzyme activities and phytohormone levels in chia seedlings. Piperonylic acid restricted chia seedling growth by reducing shoot length, fresh weight, leaf area measurements and p-coumaric acid content. Apart from sodium, piperonylic acid significantly reduced the accumulation of other essential macroelements (such as K, P, Ca and Mg) relative to the untreated control. Enhanced proline, superoxide, hydrogen peroxide and malondialdehyde contents were observed. The inhibition of trans-cinnamic acid 4-hydroxylase activity significantly increased the enzymatic activities of ROS-scavenging enzymes such as superoxide dismutase, ascorbate peroxidase, catalase and guaiacol peroxidase. In addition, piperonylic acid caused a reduction in indole-3-acetic acid and salicylic acid content. In conclusion, the reduction in chia seedling growth in response to piperonylic acid may be attributed to a reduction in p-coumaric acid content coupled with elevated ROS-induced oxidative damage, and restricted mineral and phytohormone (indole-3-acetic acid and salicylic) levels.

Inhibiting tricin biosynthesis improves maize lignocellulose saccharification

Lignin is a technological bottleneck to convert polysaccharides into fermentable sugars, and different strategies of genetic-based metabolic engineering have been applied to improve biomass saccharification. Using maize seedlings grown hydroponically for 24 h, we conducted a quick non-transgenic approach with five enzyme inhibitors of the lignin and tricin pathways. Two compounds [3,4-(methylenedioxy)cinnamic acid: MDCA and 2,4-pyridinedicarboxylic acid: PDCA] revealed interesting findings on root growth, lignin composition, and saccharification. By inhibiting hydroxycinnamoyl-CoA ligase, a key enzyme of phenylpropanoid pathway, MDCA decreased the lignin content and improved saccharification, but it decreased root growth. By inhibiting flavone synthase, a key enzyme of tricin biosynthesis, PDCA decreased total lignin content and improved saccharification without affecting root growth. PDCA was three-fold more effective than MDCA, suggesting that controlling lignin biosynthesis with enzymatic inhibitors may be an attractive strategy to improve biomass saccharification.

Multimodal biomarker discovery for active Onchocerca volvulus infection

The neglected tropical disease onchocerciasis, or river blindness, is caused by infection with the filarial nematode Onchocerca volvulus. Current estimates indicate that 17 million people are infected worldwide, the majority of them living in Africa. Today there are no non-invasive tests available that can detect ongoing infection, and that can be used for effective monitoring of elimination programs. In addition, to enable pharmacodynamic studies with novel macrofilaricide drug candidates, surrogate endpoints and efficacy biomarkers are needed but are non-existent. We describe the use of a multimodal untargeted mass spectrometry-based approach (metabolomics and lipidomics) to identify onchocerciasis-associated metabolites in urine and plasma, and of specific lipid features in plasma of infected individuals (O. volvulus infected cases: 68 individuals with palpable nodules; lymphatic filariasis cases: 8 individuals; non-endemic controls: 20 individuals). This work resulted in the identification of elevated concentrations of the plasma metabolites inosine and hypoxanthine as biomarkers for filarial infection, and of the urine metabolite cis-cinnamoylglycine (CCG) as biomarker for O. volvulus. During the targeted validation study, metabolite-specific cutoffs were determined (inosine: 34.2 ng/ml; hypoxanthine: 1380 ng/ml; CCG: 29.7 ng/ml) and sensitivity and specificity profiles were established. Subsequent evaluation of these biomarkers in a non-endemic population from a different geographical region invalidated the urine metabolite CCG as biomarker for O. volvulus. The plasma metabolites inosine and hypoxanthine were confirmed as biomarkers for filarial infection. With the availability of targeted LC-MS procedures, the full potential of these 2 biomarkers in macrofilaricide clinical trials, MDA efficacy surveys, and epidemiological transmission studies can be investigated.

Today’s diagnosis of infection with the filarial parasite Onchocerca volvulus mainly depends on the microscopic analysis of skin biopsies and serological testing. The work presented here describes the use of multiple mass spectrometry-based screening methods (metabolomics and lipidomics) to search for biomarkers indicative of infection with Onchocerca volvulus. This resulted in the identification of elevated concentrations of the plasma metabolites inosine and hypoxanthine as biomarkers for filarial infection, and of the urine metabolite cis-cinnamoylglycine as biomarker for O. volvulus. Further evaluation of these biomarkers in a geographically distinct non-endemic population however invalidated the use of urine cis-cinnamoylglycine. These findings are of utmost importance as it not only opens new avenues in the development of non-invasive diagnostic tools for filarial infections, but also emphasizes the need for evaluation and validation of newly discovered biomarkers in different populations from different geographies.

Seedling developmental defects upon blocking CINNAMATE-4-HYDROXYLASE are caused by perturbations in auxin transport

The phenylpropanoid pathway serves a central role in plant metabolism, providing numerous compounds involved in diverse physiological processes. Most carbon entering the pathway is incorporated into lignin. Although several phenylpropanoid pathway mutants show seedling growth arrest, the role for lignin in seedling growth and development is unexplored. We use complementary pharmacological and genetic approaches to block CINNAMATE-4-HYDROXYLASE (C4H) functionality in Arabidopsis seedlings and a set of molecular and biochemical techniques to investigate the underlying phenotypes. Blocking C4H resulted in reduced lateral rooting and increased adventitious rooting apically in the hypocotyl. These phenotypes coincided with an inhibition in AUX transport. The upstream accumulation in cis-cinnamic acid was found to be likely to cause polar AUX transport inhibition. Conversely, a downstream depletion in lignin perturbed phloem-mediated AUX transport. Restoring lignin deposition effectively reestablished phloem transport and, accordingly, AUX homeostasis. Our results show that the accumulation of bioactive intermediates and depletion in lignin jointly cause the aberrant phenotypes upon blocking C4H, and demonstrate that proper deposition of lignin is essential for the establishment of AUX distribution in seedlings. Our data position the phenylpropanoid pathway and lignin in a new physiological framework, consolidating their importance in plant growth and development.

Spatio-temporal control of phenylpropanoid biosynthesis by inducible complementation of a cinnamate 4-hydroxylase mutant

Cinnamate 4-hydroxylase (C4H) is a cytochrome P450-dependent monooxygenase that catalyzes the second step of the general phenylpropanoid pathway. Arabidopsis reduced epidermal fluorescence 3 (ref3) mutants, which carry hypomorphic mutations in C4H, exhibit global alterations in phenylpropanoid biosynthesis and have developmental abnormalities including dwarfing. Here we report the characterization of a conditional Arabidopsis C4H line (ref3-2pOpC4H), in which wild-type C4H is expressed in the ref3-2 background. Expression of C4H in plants with well-developed primary inflorescence stems resulted in restoration of fertility and the production of substantial amounts of lignin, revealing that the developmental window for lignification is remarkably plastic. Following induction of C4H expression in ref3-2pOpC4H, we observed rapid and significant reductions in the levels of numerous metabolites, including several benzoyl and cinnamoyl esters and amino acid conjugates. These atypical conjugates were quickly replaced with their sinapoylated equivalents, suggesting that phenolic esters are subjected to substantial amounts of turnover in wild-type plants. Furthermore, using localized application of dexamethasone to ref3-2pOpC4H, we show that phenylpropanoids are not transported appreciably from their site of synthesis. Finally, we identified a defective Casparian strip diffusion barrier in the ref3-2 mutant root endodermis, which is restored by induction of C4H expression.

Seed-coat protective neolignans are produced by the dirigent protein AtDP1 and the laccase AtLAC5 in Arabidopsis

Lignans/neolignans are generally synthesized from coniferyl alcohol (CA) in the cinnamate/monolignol pathway by oxidation to generate the corresponding radicals with subsequent stereoselective dimerization aided by dirigent proteins (DIRs). Genes encoding oxidases and DIRs for neolignan biosynthesis have not been identified previously. In Arabidopsis thaliana, the DIR AtDP1/AtDIR12 plays an essential role in the 8-O-4' coupling in neolignan biosynthesis by unequivocal structural determination of the compound missing in the atdp1 mutant as a sinapoylcholine (SC)-conjugated neolignan, erythro-3-{4-[2-hydroxy-2-(4-hydroxy-3-methoxyphenyl)-1-hydroxymethylethoxy]-3,5-dimethoxyphenyl}acryloylcholine. Phylogenetic analyses showed that AtDP1/AtDIR12 belongs to the DIR-a subfamily composed of DIRs for 8-8' coupling of monolignol radicals. AtDP1/AtDIR12 is specifically expressed in outer integument 1 cells in developing seeds. As a putative oxidase for neolignan biosynthesis, we focused on AtLAC5, a laccase gene coexpressed with AtDP1/AtDIR12. In lac5 mutants, the abundance of feruloylcholine (FC)-conjugated neolignans decreased to a level comparable to those in the atdp1 mutant. In addition, SC/FC-conjugated neolignans were missing in the seeds of mutants defective in SCT/SCPL19, an enzyme that synthesizes SC. These results strongly suggest that AtDP1/AtDIR12 and AtLAC5 are involved in neolignan biosynthesis via SC/FC. A tetrazolium penetration assay showed that seed coat permeability increased in atdp1 mutants, suggesting a protective role of neolignans in A. thaliana seeds.

Behind the Scenes: The Impact of Bioactive Phenylpropanoids on the Growth Phenotypes of Arabidopsis Lignin Mutants

The phenylpropanoid pathway converts the aromatic amino acid phenylalanine into a wide range of secondary metabolites. Most of the carbon entering the pathway incorporates into the building blocks of lignin, an aromatic polymer providing mechanical strength to plants. Several intermediates in the phenylpropanoid pathway serve as precursors for distinct classes of metabolites that branch out from the core pathway. Untangling this metabolic network in Arabidopsis was largely done using phenylpropanoid pathway mutants, all with different degrees of lignin depletion and associated growth defects. The phenotypic defects of some phenylpropanoid pathway mutants have been attributed to differentially accumulating phenylpropanoids or phenylpropanoid-derived compounds. In this perspectives article, we summarize and discuss the reports describing an altered accumulation of these bioactive molecules as the causal factor for the phenotypes of lignin mutants in Arabidopsis.

Understanding the role played by protic ionic liquids (PILs) and the substituent effect for enhancing the generation of Z-cinnamic acid derivatives†

Photoisomerization of a series of substituted E-cinnamic acids in MeCN in their acid forms and as their corresponding protic ionic liquids (PILs) with light of 300 nm is studied. The nature, strength, number, and position effects of substituents on the photochemical behavior of E-cinnamic derivatives are investigated. The photosensitization of the reaction in the presence of Michler's ketone is also studied at 366 nm and it demonstrates that the triplet-excited state is involved in the reaction. As the presence of n-butylamine needed to form the PILs significantly increases the photoproduct yields in all cases, the role of the PILs is also discussed. Thus, understanding of these fundamental aspects has allowed us to establish an excellent and practical synthetic protocol for successfully synthesizing Z-cinnamic acids.

Benzofuran-2-acetic esters as a new class of natural-like herbicides

BACKGROUND

In recent decades, the use of synthetic herbicides has been increasing, mainly in emerging countries. However, their intensive and indiscriminate application is a major cause of environmental pollution and human health injury. Therefore, there is an increasing need to develop new herbicides with safer toxicological and environmental profiles. A promising strategy is to synthesize new molecules containing the core of natural products as a template for the production of 'bio-inspired' or 'natural-like' herbicides.

RESULTS

The potential herbicidal activity of some benzofuran-2-acetic esters was assessed in vitro on Arabidopsis thaliana, a model species. All five molecules (M1-M5) showed significant phytotoxic activity, reducing both shoot and root system at low concentrations. In particular, methyl 2-(5-methoxybenzofuran-2-yl)hexanoate (M3) exhibited the highest phytotoxicity displayed against two crops and weeds, monocots (Zea mays L. and E. crus-galli) and dicots (Lactuca sativa L. and Amaranthus retroflexus L.). The M3 activity was also compared with glyphosate, a common herbicide, showing a lower but similar activity. Moreover, the results evidenced that M3 was more effective in post-emergency.

CONCLUSION

Readily synthesizable benzofuran-2-acetic esters possessing the benzofuran ring as 'bio-inspired' core, show significant herbicidal activity making them very efficient even at low concentrations. They can be sprayed in liquid form, and the addition of adjuvants can improve penetration through the leaf cuticle. These results confirm the importance of these molecules as models for the development of new natural-like herbicides. © 2019 Society of Chemical Industry.

cis-Cinnamic acid is a natural plant growth-promoting compound

Agrochemicals provide vast potential to improve plant productivity, because they are easy to implement at low cost while not being restricted by species barriers as compared with breeding strategies. Despite the general interest, only a few compounds with growth-promoting activity have been described so far. Here, we add cis-cinnamic acid (c-CA) to the small portfolio of existing plant growth stimulators. When applied at low micromolar concentrations to Arabidopsis roots, c-CA stimulates both cell division and cell expansion in leaves. Our data support a model explaining the increase in shoot biomass as the consequence of a larger root system, which allows the plant to explore larger areas for resources. The requirement of the cis-configuration for the growth-promoting activity of CA was validated by implementing stable structural analogs of both cis- and trans-CA in this study. In a complementary approach, we used specific light conditions to prevent cis/trans-isomerization of CA during the experiment. In both cases, the cis-form stimulated plant growth, whereas the trans-form was inactive. Based on these data, we conclude that c-CA is an appealing lead compound representing a novel class of growth-promoting agrochemicals. Unraveling the underlying molecular mechanism could lead to the development of innovative strategies for boosting plant biomass.

Linking phenylpropanoid metabolism, lignin deposition, and plant growth inhibition

Lignin, a polymer found in the plant secondary cell wall, is a major contributor to biomass' recalcitrance toward saccharification. Because of this negative impact toward the value of lignocellulosic crops, there is a special interest in modifying the content and composition of this important plant biopolymer. For many years this endeavor has been hindered by the plant growth inhibition that is often associated with manipulations to phenylpropanoid metabolism. Although the actual mechanism by which dwarfism arises remains unknown, recent advances in tissue-specific lignin complementation and better understanding of phenylpropanoid transcriptional regulation has made it possible to disentangle lignin modification from perturbations in plant development.

Process for the Purification of cis-p-Coumaric Acid by Cellulose Column Chromatography after the Treatment of the trans Isomer with Ultraviolet Irradiation

A methanolic solution of trans-p-coumaric acid was exposed to ultraviolet radiation and a mixture solution of the trans and cis isomers was subjected to cellulose column chromatography, eluting with an aqueous 0.1% trifluoroacetic acid solution containing methanol (90:10, v/v). Separation of the trans and cis isomers was achieved. The identity of the cis isomer was confirmed by TLC, HPLC, and NMR. Since both the support and eluent are inexpensive, the cis isomers can be obtained economically on both the laboratory and industrial scales.

Synthesis and evaluation of 1,2,3,4-tetrahydro-1-acridone analogues as potential dual inhibitors for amyloid-beta and tau aggregation

Amyloid-β (Aβ) and tau protein are two crucial hallmarks in Alzheimer's disease (AD). Their aggregation forms are thought to be toxic to the neurons in the brain. A series of new 1,2,3,4-tetrahydro-1-acridone analogues were designed, synthesized, and evaluated as potential dual inhibitors for Aβ and tau aggregation. In vitro studies showed that compounds 25-30 (20 μM) with N-methylation of the quinolone ring effectively inhibited Aβ_1-42 aggregation by 84.7%-99.5% and tau aggregation by 71.2%-101.8%. Their structure-activity relationships are discussed. In particular, 30 could permeate the blood-brain barrier, bind to Aβ_1-42 and tau, inhibit Aβ_1-42 β-sheets formation, and prevent tau aggregation in living cells.

The allelochemical trans-cinnamic acid stimulates salicylic acid production and galactose pathway in maize leaves: A potential mechanism of stress tolerance

In this study, the effects (5 days) of the secondary metabolite trans-cinnamic acid on maize leaves (Zea mays L.), through a physiological and an untargeted metabolomic approach, were evaluated. A reduction in leaf growth and development accompanied by a decrease in protein content was observed in treated seedlings. Besides, trans-cinnamic acid stimulated the photosynthetic machinery with a significant increment in pigment content (chlorophyll a, b and carotenoids), a stimulation of the light adapted PSII efficiency (ɸ_II) as well as the chlorophyll a fluorescence (Y_NO), the apparent electron transport rate, and the regulated dissipation of the energy (Y_NPQ). By contrast, the dark adapted PSII parameter (Fv/Fm) was not affected suggesting that no physical damages to the antenna complex were caused by trans-cinnamic acid. These results suggested that maize seedlings were experiencing a stress but, at the same time, were able to cope with it. This hypothesis was confirmed by both the increment in benzoic and salicylic acids, important molecules involved in stress response, and the metabolomic results, which pointed out that the seedlings are directing their metabolism towards galactose production modulating its pathway, which is pivotal for the production of the antioxidant compound ascorbic acid (ASA). Indeed, in treated plants, a significant increment in total ASA content (28%) was observed. The results suggested that the main strategy adopted by plants to cope with trans-cinnamic-induced stress consisted in the modulation of their metabolism in order to increase the total ASA and carotenoids concentration, radical scavenging species.

Involvement of an autotoxic compound in asparagus decline

Asparagus (Asparagus officinalis L.) is a widely cultivated perennial veritable and can be harvested more than ten years. However, the crop quality and yield decline after a few year's cultivation, which is called "asparagus decline". Even though those asparagus plants were replaced with new young asparagus plants, the productivity and quality of the crop remain relatively low, which is known as a "asparagus replant problem". One of the possible reasons for "asparagus decline" and "asparagus replant problem" is thought to be autotoxicity of asparagus. However, the compounds involved in the autotoxicity is not clear. The objective of this study was therefore to determine the potential role of autotoxicity in the "asparagus decline" and "asparagus replant problem". An aqueous methanol extract of 10-year-asparagus-cultivated soils inhibited the growth of asparagus seedlings and other two test plants with concentration dependent manner. The result confirmed that the asparagus soils have autotoxic activity. The extract was then purified by several chromatographies with monitoring the inhibitory activity and a potent growth inhibitory substance causing the autotoxic effect was isolated. The chemical structures of the compound was determined by spectral data to be trans-cinnamic acid. trans-Cinnamic acid inhibited the growth of asparagus seedlings at concentrations greater than 10 μM. The concentrations required for 50% growth inhibition of asparagus (IC₅₀) were 24.1-41.6 μM. trans-Cinnamic acid accumulated 174 μM in the 10-year-asparagus-cultivated soils, which may be enough levels to cause the growth inhibition on asparagus considering its IC₅₀ value. Therefore, trans-cinnamic acid may contribute to the autotoxic effect of asparagus soils, and may be in part responsible for "asparagus decline" and "asparagus replant problem".

Revising Reverse-Phase Chromatographic Behavior for Efficient Differentiation of Both Positional and Geometrical Isomers of Dicaffeoylquinic Acids

Dicaffeoylquinic acids (diCQAs) are plant metabolites and undergo trans-cis-isomerization when exposed to UV irradiation. As such, diCQAs exist in both trans- and cis-configurations and amplify the already complex plant metabolome. However, analytical differentiation of these geometrical isomers using mass spectrometry (MS) approaches has proven to be extremely challenging. Exploring the chromatographic space to develop possible conditions that would aid in differentially separating and determining the elution order of these isomers is therefore imperative. In this study, simple chromatographic parameters, such as column chemistry (phenyl versus alkyl), mobile phase composition (methanol or acetonitrile), and column temperature, were investigated to aid in the separation of diCQA geometrical isomers. The high-performance liquid chromatography photodiode array (HPLC-PDA) chromatograms revealed four isomers post UV irradiation of diCQA authentic standards. The elution profile/order was seen to vary on different reverse-phase column chemistries (phenyl versus alkyl) using different mobile phase composition. Here, the elution profile/order on the phenyl-derived column matrices (with methanol as the mobile phase composition) was observed to be relatively reproducible as compared to the alkyl (C₁₈) columns. Chromatographic resolution of diCQA geometrical isomers can be enhanced with an increase in column temperature. Lastly, the study highlights that chromatographic elution order/profile cannot be relied upon to fathom the complexity of isomeric plant metabolites.

Dereplication-Guided Isolation of New Phenylpropanoid-Substituted Diglycosides from Cistanche salsa and Their Inhibitory Activity on NO Production in Macrophage

Dereplication allows for a rapid identification of known and unknown compounds in plant extracts. In this study, we performed liquid chromatography-mass spectroscopy (LC-MS)- based dereplication using data from ESI⁺ QTOF-MS for the analysis of phenylpropanoid-substituted diglycosides, the major active constituents of Cistanche salsa (C. A. Mey.) Beck. Using TOF-MS alone, the substructures of these compounds could be unambiguously confirmed based on the characteristic fragmentation patterns of various product ions. HPLC-MS based profiling of C. salsa also allowed for the detection of new phenylpropanoid-substituted diglycosides from this plant. Of them, five new phenylpropanoid-substituted diglycosides, named cistansalsides A–E (5, 6, 12, 17 and 18), were isolated. Their structures were elucidated through spectroscopic methods including NMR and MS analysis. All the isolates were tested for their inhibitory activity against NO production in RAW 264.7 cells stimulated by LPS. Of the tested compounds, compounds 5, 11, 13 and 18 showed moderate inhibitory activity on inducible NO synthase. Compounds 11, 13 and 18 also inhibited the phosphorylation of NF-κB in macrophages. None of the compounds displayed significant cytotoxicity.

Substituent effects of cis-cinnamic acid analogues as plant growh inhibitors

1-O-cis-Cinnamoyl-β-D-glucopyranose is one of the most potent allelochemicals that has been isolated from Spiraea thunbergii Sieb by Hiradate et al. It derives its strong inhibitory activity from cis-cinnamic acid (cis-CA), which is crucial for phytotoxicity. By preparing and assaying a series of cis-CA analogues, it was previously found that the key features of cis-CA for lettuce root growth inhibition are a phenyl ring, cis-configuration of the alkene moiety, and carboxylic acid. On the basis of a structure-activity relationship study, the substituent effects on the aromatic ring of cis-CA were examined by systematic synthesis and the lettuce root growth inhibition assay of a series of cis-CA analogues having substituents on the aromatic ring. While ortho- and para-substituted analogues exhibited low potency in most cases, meta-substitution was not critical for potency, and analogues having a hydrophobic and sterically small substituent were more likely to be potent. Finally, several cis-CA analogues were found to be more potent root growth inhibitors than cis-CA.

Design and synthesis of conformationally constrained analogues of cis-cinnamic acid and evaluation of their plant growth inhibitory activity

1-O-cis-Cinnamoyl-β-D-glucopyranose is known to be one of the most potent allelochemical candidates and was isolated from Spiraea thunbergii Sieb by Hiradate et al. (2004), who suggested that it derived its strong inhibitory activity from cis-cinnamic acid, which is crucial for phytotoxicity. In this study, key structural features and substituent effects of cis-cinnamic acid (cis-CA) on lettuce root growth inhibition was investigated. These structure-activity relationship studies indicated the importance of the spatial relationship of the aromatic ring and carboxylic acid moieties. In this context, conformationally constrained cis-CA analogues, in which the aromatic ring and cis-olefin were connected by a carbon bridge, were designed, synthesized, and evaluated as plant growth inhibitors. The results of the present study demonstrated that the inhibitory activities of the five-membered and six-membered bridged compounds were enhanced, up to 0.27 μM, and were ten times higher than cis-CA, while the potency of the other compounds was reduced.

Key structural features of cis-cinnamic acid as an allelochemical

1-O-cis-cinnamoyl-β-D-glucopyranose is one of the most potent allelochemicals isolated from Spiraea thunbergii Sieb. It is suggested that it derives its strong inhibitory activity from cis-cinnamic acid, which is crucial for phytotoxicity. It was synthesized to confirm its structure and bioactivity, and also a series of cis-cinnamic acid analogues were prepared to elucidate the key features of cis-cinnamic acid for lettuce root growth inhibition. The cis-cyclopropyl analogue showed potent inhibitory activity while the saturated and alkyne analogues proved to be inactive, demonstrating the importance of the cis-double bond. Moreover, the aromatic ring could not be replaced with a saturated ring. However, the 1,3-dienylcyclohexene analogue showed strong activity. These results suggest that the geometry of the C-C double bond between the carboxyl group and the aromatic ring is essential for potent inhibitory activity. In addition, using several light sources, the photostability of the cinnamic acid derivatives and the role of the C-C double bond were also investigated.

Acquired immunity of transgenic torenia plants overexpressing agmatine coumaroyltransferase to pathogens and herbivore pests

We investigated the ability of transgenic torenia (Scrophulariaceae) plants to resist fungi and arthropod herbivores. Torenia hybrida cv. Summerwave Blue was manipulated to produce Arabidopsis agmatine coumaroyltransferase (AtACT). This catalyses the last step in the biosynthesis of hydroxycinnamic acid amides (HCAAs) which function in defence. Transgenic plants accumulated substantial HCAAs, predominantly p-coumaroylagmatine, and the HCAAs were isomerized from the trans-form to the cis-form in planta. The transgenic line, accumulated the highest amount of endogenous HCAAs (CouAgm at 32.2 µM and total HCAAs at 47.5 µM) and this line was resistant to the necrotrophic fungus, Botrytis cinerea. There was no resistance, however, in their wild-type progenitors or in other transgenic lines accumulating low HCAA amounts. In contrast, the transformants were not significantly resistant to three representative herbivores, Frankliniella occidentalis, Aphis gossypii, and Tetranychus ludeni.

A comparative study on the effectiveness of cis- and trans-form of cinnamic acid treatments for inhibiting invasive activity of human lung adenocarcinoma cells

Lung cancer is the major cause of tumor-related death, and approximately 70% of lung cancer patients die from metastasis. Evidence that phenolic compounds may have a potential inhibitory effect on cancer invasion and metastasis is increasingly being reported in the scientific literature. Cinnamic acid is a member of phenolics which having several isoforms in nature. The trans-cinnamic acid (t-CA) has been investigated extensively for its potential pharmacological effects whereas the study of cis-cinnamic acid (c-CA) is limited because pure c-CA was hard to obtain. We had developed a practicable method previously to transform and obtain pure c-CA, and the pure compound was used to evaluate the anti-invasive effect on human adenocarcinoma A549 cells. The A549 cells were treated with 0-200 μM of c-CA and t-CA in the presence of 200 nM phorbol-12-myristate-13-acetate (PMA) at 37 °C for 24 h, and matrix metalloproteinase (MMP)-2, MMP-9, adhesive, migratory, and invasive activities of the cells were determined. The results showed that the treatment of c-CA and t-CA dose-dependently reduced the PMA-induced MMP-2 and -9 activities but without significant effect on the adhesive activity of cells. The PMA-induced motility was suppressed in a dose-dependent manner by a 24-h treatment with c-CA and t-CA. The invasive ability was significantly (p<0.05) reduced to 68% and 65%, respectively, relative to PMA treatment alone after treatment of PMA-treated A549 cells with either 50 μM c-CA or 100 μM t-CA for 24 h. The results suggest that both of the c-CA and t-CA are inhibitors for invasion of A549 cells and the activity of c-CA seems to be higher than t-CA.

Cis-cinnamic acid-enhanced 1 gene plays a role in regulation of Arabidopsis bolting

Cis-cinnamic acid (CA) is one of many cis-phenylpropanoids found in both monocots and dicots. It is produced in planta via sunlight-mediated isomerization of trans-cinnamic acid. This pair of isomers plays a differential role in regulation of plant growth. A functional proteomics approach has been adopted to identify genes of cis/trans-CA mixture-enhanced expression. Out of 1,241 proteins identified by mass spectrometry, 32 were CA-enhanced and 13 repressed. Further analysis with the molecular biology approach revealed 2 cis-CA (Z usammen-CA)-E nhanced genes, named ZCE1 and ZCE2, which encode members of the major latex protein-like (MLPL) gene family. The transcript accumulation of both genes is positively correlated with the amount of cis-CA applied externally, ranging from 1 to 100 μM. ZCE1 transcript accumulation is enhanced largely by cis-CA and slightly by other cis-phenylpropanoids. Treatment of several well-characterized plant growth regulator perception-deficient mutants with cis-CA is able to promote ZCE1 transcript accumulation, suggestive of distinct signaling pathways regulating cis-CA response. The zce1 loss-of-function mutant produced via the RNA-interference technique produces an earlier bolting phenotype in Arabidopsis, suggesting that ZCE1 plays a role in promoting vegetative growth and delay flowering.

The origin and evolution of lignin biosynthesis

Lignin, a phenolic polymer derived mainly from hydroxycinnamyl alcohols, is ubiquitously present in tracheophytes. The development of lignin biosynthesis has been considered to be one of the key factors that allowed land plants to flourish in terrestrial ecosystems. Lignin provides structural rigidity for tracheophytes to stand upright, and strengthens the cell wall of their water-conducting tracheary elements to withstand the negative pressure generated during transpiration. In this review, we discuss a number of aspects regarding the origin and evolution of lignin biosynthesis during land plant evolution, including the establishment of its monomer biosynthetic scaffold, potential precursors to the lignin polymer, as well as the emergence of the polymerization machinery and regulatory system. The accumulated knowledge on the topic, as summarized here, provides us with an evolutionary view on how this complex metabolic system emerged and developed.

Mutations in the cinnamate 4-hydroxylase gene impact metabolism, growth and development in Arabidopsis

The initial reactions of the phenylpropanoid pathway convert phenylalanine to p-coumaroyl CoA, a branch point metabolite from which many phenylpropanoids are made. Although the second enzyme of this pathway, cinnamic acid 4-hydroxylase (C4H), is well characterized, a mutant for the gene encoding this enzyme has not yet, to our knowledge, been identified, presumably because knock-out mutations in this gene would have severe phenotypes. This work describes the characterization of an allelic series of Arabidopsis reduced epidermal fluorescence 3 (ref3) mutants, each of which harbor mis-sense mutations in C4H (At2g30490). Heterologous expression of the mutant proteins in Escherichia coli yields enzymes that exhibit P420 spectra, indicative of mis-folded proteins, or have limited ability to bind substrate, indicating that the mutations we have identified affect protein stability and/or enzyme function. In agreement with the early position of C4H in phenylpropanoid metabolism, ref3 mutant plants accumulate decreased levels of several different classes of phenylpropanoid end-products, and exhibit reduced lignin deposition and altered lignin monomer content. Furthermore, these plants accumulate a novel hydroxycinnamic ester, cinnamoylmalate, which is not found in the wild type. The decreased C4H activity in ref3 also causes pleiotropic phenotypes, including dwarfism, male sterility and the development of swellings at branch junctions. Together, these observations indicate that C4H function is critical to the normal biochemistry and development of Arabidopsis.