Catechin is a phytototoxin and a pro-oxidant secreted from the roots of Centaurea stoebe

A Specific Protective Mechanism Against Chloroplast Photo-Reactive Oxygen Species in Phosphate-Starved Rice Plants

Phosphorus (Pi) starvation prevents a good match between light energy absorption and photosynthetic carbon metabolism, generating photo-reactive oxygen species (photo-ROS) in chloroplasts. Plants have evolved to withstand photo-oxidative stress, but the key regulatory mechanism underlying it remains unclear. In rice (Oryza sativa), DEEP GREEN PANICLE1 (DGP1) is robustly up-regulated in response to Pi deficiency. DGP1 decreases the DNA-binding capacities of the transcriptional activators GLK1/2 on the photosynthetic genes involved in chlorophyll biosynthesis, light harvesting, and electron transport. This Pi-starvation-induced mechanism dampens both electron transport rates through photosystem I and II (ETRI and ETRII) and thus mitigates the electron-excessive stress in mesophyll cells. Meanwhile, DGP1 hijacks glycolytic enzymes GAPC1/2/3, redirecting glucose metabolism toward the pentose phosphate pathway with superfluous NADPH production. Phenotypically, light irradiation induces O2 - production in Pi-starved WT leaves but is observably accelerated in dgp1 mutant and impaired in GAPCsRNAi and glk1glk2 lines. Interestingly, overexpressed DGP1 in rice caused hyposensitivity to ROS-inducers (catechin and methyl viologen), but the dgp1 mutant shows a similar inhibitory phenotype with the WT seedlings. Overall, the DGP1 gene serves as a specific antagonizer against photo-ROS in Pi-starved rice plants, which coordinates light-absorbing and anti-oxidative systems by orchestrating transcriptional and metabolic regulations, respectively.

Specialized Metabolites Accumulation Pattern in Buckwheat Is Strongly Influenced by Accession Choice and Co-Existing Weeds

Screening suitable allelopathic crops and crop genotypes that are competitive with weeds can be a sustainable weed control strategy to reduce the massive use of herbicides. In this study, three accessions of common buckwheat Fagopyrum esculentum Moench. (Gema, Kora, and Eva) and one of Tartary buckwheat Fagopyrum tataricum Gaertn. (PI481671) were screened against the germination and growth of the herbicide-resistant weeds Lolium rigidum Gaud. and Portulaca oleracea L. The chemical profile of the four buckwheat accessions was characterised in their shoots, roots, and root exudates in order to know more about their ability to sustainably manage weeds and the relation of this ability with the polyphenol accumulation and exudation from buckwheat plants. Our results show that different buckwheat genotypes may have different capacities to produce and exude several types of specialized metabolites, which lead to a wide range of allelopathic and defence functions in the agroecosystem to sustainably manage the growing weeds in their vicinity. The ability of the different buckwheat accessions to suppress weeds was accession-dependent without differences between species, as the common (Eva, Gema, and Kora) and Tartary (PI481671) accessions did not show any species-dependent pattern in their ability to control the germination and growth of the target weeds. Finally, Gema appeared to be the most promising accession to be evaluated in organic farming due to its capacity to sustainably control target weeds while stimulating the root growth of buckwheat plants.

Phytotoxicity and allelopathic potential of Juglans regia L. leaf extract

Implementation of plant extracts that are rich in phytochemicals and have the allelopathic potential for weed management could help reduce the use of chemical herbicides. The present study investigated the herbicidal potential of walnut (Juglans regia L.) leaf extract (WLE) against two weeds, Amaranthus retroflexus L. and Chenopodium album L., by testing in vitro their seed germination and seedling growth, and then evaluated in vivo the oxidative stress of potted plants. The effects of the walnut leaf extract were also tested on maize (Zea mays L.) to eliminate possible negative impacts on a cultivated plant. Total phenolic acids and total flavonoid content in the extract were determined in prior bioassays, followed by separation and analysis of flavonoids and phenolic acids by high-performance liquid chromatography (HPLC). Phytochemical analysis revealed that the obtained extract was notably rich in phenolic compounds, while HPLC analysis confirmed the presence of (+)-catechin, luteolin, myricetin, rutin, (-)-epicatechin, genistin, protocatechuic acid, and caffeic acid as major extract components. The results obtained in bioassays revealed a significant negative impact of the walnut leaf extract on germination and seedling growth of the tested weeds, as well as significant oxidative stress in weeds grown in pots. Although it affected the maize seedling growth in vitro similar to the tested weeds, maize germination was less sensitive to treatment, and the extract did not have a significant negative impact in terms of oxidative stress in maize plants grown in pots. The findings show that walnut leaf extract may have a promising role in replacing chemical herbicides in maize.

Tyr-Asp inhibition of glyceraldehyde 3-phosphate dehydrogenase affects plant redox metabolism

How organisms integrate metabolism with the external environment is a central question in biology. Here, we describe a novel regulatory small molecule, a proteogenic dipeptide Tyr-Asp, which improves plant tolerance to oxidative stress by directly interfering with glucose metabolism. Specifically, Tyr-Asp inhibits the activity of a key glycolytic enzyme, glyceraldehyde 3-phosphate dehydrogenase (GAPC), and redirects glucose toward pentose phosphate pathway (PPP) and NADPH production. In line with the metabolic data, Tyr-Asp supplementation improved the growth performance of both Arabidopsis and tobacco seedlings subjected to oxidative stress conditions. Moreover, inhibition of Arabidopsis phosphoenolpyruvate carboxykinase (PEPCK) activity by a group of branched-chain amino acid-containing dipeptides, but not by Tyr-Asp, points to a multisite regulation of glycolytic/gluconeogenic pathway by dipeptides. In summary, our results open the intriguing possibility that proteogenic dipeptides act as evolutionarily conserved small-molecule regulators at the nexus of stress, protein degradation, and metabolism.

A Multi-OMICs Approach Sheds Light on the Higher Yield Phenotype and Enhanced Abiotic Stress Tolerance in Tobacco Lines Expressing the Carrot lycopene β-cyclase1 Gene

Recently, we published a set of tobacco lines expressing the Daucus carota (carrot) DcLCYB1 gene with accelerated development, increased carotenoid content, photosynthetic efficiency, and yield. Because of this development, DcLCYB1 expression might be of general interest in crop species as a strategy to accelerate development and increase biomass production under field conditions. However, to follow this path, a better understanding of the molecular basis of this phenotype is essential. Here, we combine OMICs (RNAseq, proteomics, and metabolomics) approaches to advance our understanding of the broader effect of LCYB expression on the tobacco transcriptome and metabolism. Upon DcLCYB1 expression, the tobacco transcriptome (~2,000 genes), proteome (~700 proteins), and metabolome (26 metabolites) showed a high number of changes in the genes involved in metabolic processes related to cell wall, lipids, glycolysis, and secondary metabolism. Gene and protein networks revealed clusters of interacting genes and proteins mainly involved in ribosome and RNA metabolism and translation. In addition, abiotic stress-related genes and proteins were mainly upregulated in the transgenic lines. This was well in line with an enhanced stress (high light, salt, and H₂O₂) tolerance response in all the transgenic lines compared with the wild type. Altogether, our results show an extended and coordinated response beyond the chloroplast (nucleus and cytosol) at the transcriptome, proteome, and metabolome levels, supporting enhanced plant growth under normal and stress conditions. This final evidence completes the set of benefits conferred by the expression of the DcLCYB1 gene, making it a very promising bioengineering tool to generate super crops.

Bioactivites of two common polyphenolic compounds: Verbascoside and catechin

CONTEXT

Natural products can present remarkable biological and pharmacological activities. In traditional medicine, plants have been used historically in treating cancer, infections, and other inflammatory conditions.

OBJECTIVE

Verbascoside and catechin are widespread polyphenolic plant compounds that could play a role in the anti-inflammatory and health-promoting effects of plants and plant extracts.

MATERIALS AND METHODS

This study compares the potential cytotoxic effects of polyphenols verbascoside and catechin (6.25-200 µM) on human peripheral blood mononuclear cells (PBMC) for 48 h and myelomonocytic THP-1 and THP-1 Blue cells for 24 h. The effects of the compounds on immune activation markers such as indoleamine 2,3-dioxygenase (IDO) activity as well as on neopterin formation and nuclear factor-κB (NF-κB) activation were investigated. Cytotoxicity of the compounds was tested using Cell-Titer Blue assay.

RESULTS

Verbascoside exhibited significant suppressive effects in mitogen-stimulated PBMC on tryptophan breakdown (>50 µM; IC50 value: 58.6 µM) and the production of neopterin (>6.25 µM; IC50 value: 217 µM). These effects correlated with a decline in cell viability, while THP-1 Blue cells were less sensitive. NF-κB activity was slightly enhanced at lower concentrations (<50 µM verbascoside) in stimulated cells and at the highest concentration used in unstimulated cells. Catechin had no relevant effects on cell viability and on the tested inflammation markers, except NF-κB activation in THP-1 Blue cells.

DISCUSSION AND CONCLUSION

The results obtained show that verbascoside and catechin represent effective compounds which interfere with immunobiochemical pathways that are highly relevant for immunosurveillance and competing virus infections.

Regular consumption of black tea increases circulating kynurenine concentrations: A randomized controlled trial

BACKGROUND

Circulating neopterin and the ratio of kynurenine to tryptophan (KYN/TRP) concentrations are biomarkers of immune activation that have been linked to cardiovascular and total mortality. Several in vitro studies indicated that tea flavonoids and other antioxidants can modulate tryptophan breakdown rates and neopterin production in immune cells. We aimed to assess the effects of regular black tea consumption on tryptophan and neopterin metabolisms in vivo.

METHODS

Participants were healthy individuals, with no major illnesses and having normal to mildly elevated systolic blood pressure. They were randomly assigned to consume 3 cups/day of either powdered black tea solids (tea; n = 45) or a flavonoid-free caffeine-matched beverage (control; n = 49). Serum concentrations of tryptophan, kynurenine and neopterin were assessed at baseline and again at 3 and 6 months after daily ingestion of the respective beverage.

RESULTS

Regular consumption of tea over 6 months, compared to control, did not significantly alter neopterin (p = 0.13) or tryptophan (p = 0.85) concentrations, but did result in significantly higher kynurenine (p = 0.016) and KYN/TRP (p = 0.012). Relative to the control group, in the tea group kynurenine and KYN/TRP increased during the treatment period by 0.28 μmol/L (95% CI: - 0.04, 0.60) and 3.2 μmol/mmol (95% CI: - 1.6, 8.0), respectively at 3 months, and by 0.48 μmol/L (95% CI: 0.16, 0.80) and 7.5 μmol/mmol (95% CI: 2.5, 12.5), respectively at 6 months.

CONCLUSIONS

Increased circulation of kynurenine and KYN/TRP following regular black tea consumption may indicate enhanced tryptophan breakdown, possibly due to immune activation-induced tryptophan degrading enzyme indoleamine 2,3-dioxygenase.

GENERAL SIGNIFICANCE

The influence of black tea consumption on biomarkers of immune system activation could relate to its general health benefits. Data suggests that the net effect strongly depends on the individual immune state, being stimulatory in healthy individuals, while acting more immune dampening in situations with an inflammatory background.

Allelopathic potential of Rapanea umbellata leaf extracts

The stressful conditions associated with the Brazilian savanna (Cerrado) environment were supposed to favor higher levels of allelochemicals in Rapanea umbellata from this ecosystem. The allelopathic potential of R. umbellata leaf extracts was studied using the etiolated wheat coleoptile and standard phytotoxicity bioassays. The most active extract was selected to perform a bioassay-guided isolation, which allowed identifying lutein (1) and (-)-catechin (2) as potential allelochemicals. Finally, the general bioactivity of the two compounds was studied, which indicated that the presence of 1 might be part of the defense mechanisms of this plant.

Catechin secretion and phytotoxicity: Fact not fiction

Research indicates that the invasiveness of Centaurea stoebe is attributed to the stronger allelopathic effects on the native North American species than on the related European species, which is one of the unquestionable aspects of the "novel weapons hypothesis (NWH)." Studies originating from controlled to field conditions have shown that C. stoebe utilizes its biochemical potential to exert its invasiveness. The roots of C. stoebe secrete a potent phytotoxin, catechin, which has a detrimental effect on the surrounding plant species. Although, studies on catechin secretion and phytotoxicity represent one of the most well studied systems describing negative plant-plant interactions, it has also sparked controversies lately due to its phytotoxicity dosages and secretion effluxes. Previous reports negate the phytotoxic and pro-oxidant nature of catechin.1-3 In our recent study we have shown that catechin is highly phytotoxic against Arabidopsis thaliana and Festuca idahoensis. We also show that (±) catechin applied to roots of A. thaliana induces reactive oxygen species (ROS) confirming the pro-oxidant nature of catechin. In addition, activation of signature cell death genes such as acd2 and cad1 post catechin treatment in A. thaliana ascertains the phytotoxic nature of catechin.