Stress-induced flavonoid biosynthesis and the antioxidant machinery of plants

Effects of derivatization and probiotic transformation on the antioxidative activity of fruit polyphenols

Fruits contain numerous polyphenols in the form of conjugates, which exhibit low antioxidant activity. Probiotic fermentation is a strategy to improve the antioxidant activity of these conjugated polyphenols by modifying their structure. However, the mechanisms underlying the effects of functional groups and derivatizations on the antioxidative activities of polyphenols and the antioxidation enhancement by probiotic biotransformation haven't been comprehensively explored. This review aimed to explore the structure-antioxidant activity relationships of four functional groups and three derivatizations in flavonoids and phenolic acids. Further, the review elucidated the antioxidant mechanisms underlying the biotransformation of flavonoids and phenolic acids as glycoside, methylated, and ester conjugates by probiotic biotransformation. Deglycosylation, demethylation, and hydrolysis catalyzed by enzymes produced by Bifidobacterium and Lactobacillus facilitated the conversion of conjugated polyphenols into flavonoids and phenolic acids with hydrolyzed forms and highly active functional groups, thereby increasing hydrogen supply and electron transfer capacity to enhance the antioxidant activity.

Chromatic covalent organic frameworks enabling in-vivo chemical tomography

Covalent organic frameworks designed as chromatic sensors offer opportunities to probe biological interfaces, particularly when combined with biocompatible matrices. Particularly compelling is the prospect of chemical tomography - or the 3D spatial mapping of chemical detail within the complex environment of living systems. Herein, we demonstrate a chromic Covalent Organic Framework (COF) integrated within silk fibroin (SF) microneedles that probe plant vasculature, sense the alkalization of vascular fluid as a biomarker for drought stress, and provide a 3D in-vivo mapping of chemical gradients using smartphone technology. A series of Schiff base COFs with tunable pKa ranging from 5.6 to 7.6 enable conical, optically transparent SF microneedles with COF coatings of 120 to 950 nm to probe vascular fluid and the surrounding tissues of tobacco and tomato plants. The conical design allows for 3D mapping of the chemical environment (such as pH) at standoff distances from the plant, enabling in-vivo chemical tomography. Chromatic COF sensors of this type will enable multidimensional chemical mapping of previously inaccessible and complex environments.

Polyamines and hydrogen peroxide: Allies in plant resilience against abiotic stress

The increasing prevalence and severity of abiotic stresses on plants due to climate change is among the crucial issues of decreased crop productivity worldwide. These stresses affect crop productivity and pose a challenge to food security. Polyamines (Pas) and hydrogen peroxide (H₂O₂) could play a vital role to minimize the impact of several abiotic stresses on the plants. Pas are small molecules that regulate various physiological and developmental processes in plants and confer stress tolerance and protection against dehydration and cellular damage. Pas also interact with plant growth regulators and participate in various signaling routes that can mediate stress response. H₂O₂ on the other hand, acts as a signaling agent and plays a pivotal part in controlling crop growth and productivity. It can trigger oxidative damage at high levels but acts as a stress transducer and regulator at low concentrations. H₂O₂ is involved in stress defense mechanisms and the activation of genes involved in conferring tolerance. Therefore, the main focus of this paper is to explore roles of Pas and H₂O₂ in plant responses to various abiotic stress, highlighting their involvement in stress retaliation and signaling routes. Emphasis has been placed on understanding how Pas and H₂O₂ function and interact with other signaling molecules. Also, interaction of Pas and H₂O₂ with calcium ions, abscisic acid and nitrogen has been discussed, along with activation of MAPK cascade. This additive understanding could contribute to adopt strategies to improve crop productivity and enhance plant resilience to environmental challenges.

Physiological and molecular responses of strawberry plants to Cd stress

Cadmium (Cd), a toxic metal element, can be absorbed by plants via divalent metal ion transporters, thereby retarding plant growth and posing a threat to human health. Strawberries are popular and economically valuable berry species that are sensitive to soil pollutants, especially Cd. However, the mechanisms underlying Cd stress responses in strawberry plants remain largely unclear. Here, we investigated the physiological and molecular basis of Cd stress responses in strawberry plants using the diploid strawberry 'Yellow Wonder' as a material. The results indicated that Cd stress induced oxidative damage, repressed photosynthetic efficiency, and interfered with the accumulation and redistribution of trace elements. Furthermore, Cd stress reduced the concentrations of indoleacetic acid, trans-zeatin riboside and gibberellic acid while increasing the concentration of abscisic acid, thus altering the phytohormone signaling pathway in strawberry plants. Cd stress also inhibited the expression of genes involved in nitrogen uptake and assimilation while promoting the energy supply for plant survival under Cd toxicity. Moreover, the flavonoid biosynthesis pathway was induced, and the anthocyanin concentration increased, thereby improving the free radical scavenging capacity of strawberry plants under Cd toxicity. Additionally, we identified several transcription factors and functional genes as hub genes based on a weighted gene coexpression network analysis. These results collectively provide a theoretical foundation for strawberry breeding and ensuring agriculture and food safety.

UGT gene family identification and functional analysis of HvUGT1 under drought stress in wild barley

Drought stress poses a significant threat to global agriculture, highlighting the urgent need to elucidate the molecular mechanisms underlying plant drought tolerance. The UDP-glycosyltransferase (UGT) gene family plays crucial roles in diverse biological processes in plants. In this study, we conducted a comprehensive analysis of the UGT gene family in wild barley EC_S1, focusing on gene characteristics, subcellular localization, phylogenetic relationships, and protein structure. A total of 175 UGT gene family members were identified, exhibiting diverse patterns in protein length, molecular weight, isoelectric point, hydrophilicity, and subcellular localization. Most genes are located at chromosome ends. Phylogenetic analysis grouped the UGT genes into seven clusters, with barley-specific group E. Expression analysis across barley tissues showed upregulation in roots and senescent leaves, implying diverse roles. Under drought stress, expression patterns varied, with drought-tolerant varieties showing fewer changes than sensitive ones. Clustering analysis revealed distinct expression patterns, suggesting regulatory functions in barley's drought response. As a case, the HvUGT1 was cloned. Overexpression of HvUGT1 in Arabidopsis enhanced drought tolerance, with increased water retention, reduced cell damage, and elevated flavonoid levels. Conversely, HvUGT1 silencing in wild barley decreased drought tolerance, accompanied by reduced antioxidant enzyme activity and flavonoid content. These results highlight HvUGT1's importance in enhancing plant drought tolerance, possibly through flavonoid-mediated ROS clearance. The research provides gene resources and valuable insights for the development of drought-resistant crops through targeted genetic manipulation strategies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-024-01487-w.

Transcriptome and metabolome analysis reveal key genes and metabolic pathway responses in Leersia hexandra Swartz under Cr and Ni co-stress

Phytoremediation, an eco-friendly approach for mitigating heavy metal contamination, is reliant on hyperaccumulators. This study focused on Leersia hexandra Swart, a known chromium (Cr) hyperaccumulator with demonstrated tolerance to multiple heavy metals. Our objective was to investigate its response to simultaneous Cr and nickel (Ni) stress over 12 days. Results from physiological experiments demonstrated a significant increase in the activities of antioxidant enzymes (APX, SOD, CAT) and glutathione (GSH) content under Cr and Ni stress, indicating enhanced antioxidant mechanisms. Transcriptome analysis revealed that stress resulted in the differential expression of 27 genes associated with antioxidant activity and metal binding, including APX, SOD, CAT, GSH, metallothionein (MT), and nicotinamide (NA). Among them, twenty differentially expressed genes (DEGs) related to GSH metabolic cycle were identified. Notably, GSTU6, GND1, and PGD were the top three related genes, showing upregulation with fold changes of 4.57, 6.07, and 3.76, respectively, indicating their crucial role in metal tolerance. The expression of selected DEGs was validated by quantitative real-time PCR, confirming the reliability of RNA-Seq data. Metabolomic analysis revealed changes in 1121 metabolites, with amino acids, flavonoids, and carbohydrates being the most affected. Furthermore, glucosinolate biosynthesis and amino acid biosynthesis pathways were represented in the KEGG pathway of differentially expressed metabolites (DEMs). This study provides insights into the tolerance mechanisms of L. hexandra under the co-stress of Cr and Ni, offering a new perspective for enhancing its remediation performance.

Effects of High Salinity and Water Stress on Wetland Grasses from the Spanish Mediterranean Coast

The impacts of climate change are reaching unprecedented levels, heightening the risk of species loss and ecosystem service degradation. Wetlands, highly threatened ecosystems, serve vital ecological functions by capturing carbon, filtering water, and harbouring diverse wildlife. Coastal wetlands encounter many challenges, such as increased drought periods and escalating salinity levels, severely impacting plant biodiversity. Assessing how plants respond to various environmental stress factors is imperative for devising successful conservation strategies. In the present study, we examined three representative grass species found in various habitats within the Albufera Natural Park, close to the city of Valencia on the Spanish Mediterranean coast: Imperata cylindrica, Phragmites australis, and Saccharum ravennae. High salinity and water stress conditions were induced by subjecting the plants to irrigation with solutions containing 200, 400, 600, and 800 mM NaCl or withholding irrigation altogether to mimic coastal flooding and drought scenarios. The treatments were maintained until noticeable wilting of the plants occurred, at which point a range of stress biomarkers were determined, including photosynthetic pigments, ions, osmolytes, oxidative stress markers, and antioxidant metabolites, as well as antioxidant enzyme activities. Saccharum ravennae displayed the highest sensitivity to salt stress, whereas I. cylindrica appeared to be the most tolerant. The primary salinity tolerance mechanism observed in I. cylindrica and P. australis was a blockage of ion transport from the root zone to the aerial part, together with the salt-induced accumulation of proline and soluble sugars to high concentrations in the former. No significant effects of the water deficit treatment on the growth or biochemical parameters were observed for any of the analysed species. These findings offer valuable information for the effective management and conservation of coastal wetlands facing the challenges posed by climate change.

Rhizophagus Irregularis regulates flavonoids metabolism in paper mulberry roots under cadmium stress

Broussonetia papyrifera is widely found in cadmium (Cd) contaminated areas, with an inherent enhanced flavonoids metabolism and inhibited lignin biosynthesis, colonized by lots of symbiotic fungi, such as arbuscular mycorrhizal fungi (AMF). However, the physiological and molecular mechanisms by which Rhizophagus irregularis, an AM fungus, regulates flavonoids and lignin in B. papyrifera under Cd stress remain unclear. Here, a pot experiment of B. papyrifera inoculated and non-inoculated with R. irregularis under Cd stress was carried out. We determined flavonoids and lignin concentrations in B. papyrifera roots by LC-MS and GC-MS, respectively, and measured the transcriptional levels of flavonoids- or lignin-related genes in B. papyrifera roots, aiming to ascertain the key components of flavonoids or lignin, and key genes regulated by R. irregularis in response to Cd stress. Without R. irregularis, the concentrations of eriodictyol, quercetin and myricetin were significantly increased under Cd stress. The concentrations of eriodictyol and genistein were significantly increased by R. irregularis, while the concentration of rutin was significantly decreased. Total lignin and lignin monomer had no alteration under Cd stress or with R. irregularis inoculation. As for flavonoids- or lignin-related genes, 26 genes were co-regulated by Cd stress and R. irregularis. Among these genes, BpC4H2, BpCHS8 and BpCHI5 were strongly positively associated with eriodictyol, indicating that these three genes participate in eriodictyol biosynthesis and were involved in R. irregularis assisting B. papyrifera to cope with Cd stress. This lays a foundation for further research revealing molecular mechanisms by which R. irregularis regulates flavonoids synthesis to enhance tolerance of B. papyrifera to Cd stress.

Nanoplastic toxicity induces metabolic shifts in Populus × euramericana cv. '74/76' revealed by multi-omics analysis

There is increasing global concern regarding the pervasive issue of plastic pollution. We investigated the response of Populus × euramericana cv. '74/76' to nanoplastic toxicity via phenotypic, microanatomical, physiological, transcriptomic, and metabolomic approaches. Polystyrene nanoplastics (PS-NPs) were distributed throughout the test plants after the application of PS-NPs. Nanoplastics principally accumulated in the roots; minimal fractions were translocated to the leaves. In leaves, however, PS-NPs easily penetrated membranes and became concentrated in chloroplasts, causing thylakoid disintegration and chlorophyll degradation. Finally, oxidant damage from the influx of PS-NPs led to diminished photosynthesis, stunted growth, and etiolation and/or wilting. By integrating dual-omics data, we found that plants could counteract mild PS-NP-induced oxidative stress through the antioxidant enzyme system without initiating secondary metabolic defense mechanisms. In contrast, severe PS-NP treatments promoted a shift in metabolic pattern from primary metabolism to secondary metabolic defense mechanisms, an effect that was particularly pronounced during the upregulation of flavonoid biosynthesis. Our findings provide a useful framework from which to further clarify the roles of key biochemical pathways in plant responses to nanoplastic toxicity. Our work also supports the development of effective strategies to mitigate the environmental risks of nanoplastics by biologically immobilizing them in contaminated lands.

Short-term test for the toxicogenomic assessment of ecotoxic modes of action in Myriophyllum spicatum

In environmental risk assessment of substances, the 14-day growth inhibition test following OECD test guideline 239 is employed to assess toxicity in the macrophyte Myriophyllum spicatum. Currently, this test evaluates physiological parameters and does not allow the identification of the mode of action (MoA) by which adverse effects are induced. However, for an improved ecotoxicity assessment of substances, knowledge about their ecotoxic MoA in non-target organisms is required. It has previously been suggested that the identification of gene expression changes can contribute to MoA identification. Therefore, we developed a shortened three-day assay for M. spicatum including the transcriptomic assessment of global gene expression changes and applied this assay to two model substances, the herbicide and photosynthesis inhibitor bentazone and the pharmaceutical and HMG-CoA reductase inhibitor atorvastatin. Due to the lack of a reference genome for M. spicatum we performed a de novo transcriptome assembly followed by a functional annotation to use the toxicogenomic results for MoA discrimination. The gene expression changes induced by low effect concentrations of these substances were used to identify differentially expressed genes (DEGs) and impaired biological functions for the respective MoA. We observed both concentration-dependent numbers and differentiated patterns of DEGs for both substances. While bentazone impaired genes involved in the response to reactive oxygen species as well as light response, and also genes involved in developmental processes, atorvastatin exposure led to a differential regulation of genes related to brassinosteroid response as well as potential metabolic shifts between the mevalonate and methyl erythritol 4-phosphate pathway. Based on these responses, we identified biomarker candidates for the assessment of MoA in M. spicatum. Utilizing the shortened assay developed in this study, the investigation of the identified biomarker candidates may contribute to the development of future MoA-specific screening approaches in the ecotoxicological hazard prediction using aquatic non-standard model organisms.

Identification of a candidate gene for the I locus determining the dominant white bulb color in onion (Allium cepa L.)

KEY MESSAGE

Through a map-based cloning approach, a gene coding for an R2R3-MYB transcription factor was identified as a causal gene for the I locus controlling the dominant white bulb color in onion. White bulb colors in onion (Allium cepa L.) are determined by either the C or I loci. The causal gene for the C locus was previously isolated, but the gene responsible for the I locus has not been identified yet. To identify candidate genes for the I locus, an approximately 7-Mb genomic DNA region harboring the I locus was obtained from onion and bunching onion (A. fistulosum) whole genome sequences using two tightly linked molecular markers. Within this interval, the AcMYB1 gene, known as a positive regulator of anthocyanin production, was identified. No polymorphic sequences were found between white and red AcMYB1 alleles in the 4,860-bp full-length genomic DNA sequences. However, a 4,838-bp LTR-retrotransposon was identified in the white allele, in the 79-bp upstream coding region from the stop codon. The insertion of this LTR-retrotransposon created a premature stop codon, resulting in the replacement of 26 amino acids with seven different residues. A molecular marker was developed based on the insertion of this LTR-retrotransposon to genotype the I locus. A perfect linkage between bulb color phenotypes and marker genotypes was observed among 5,303 individuals of segregating populations. The transcription of AcMYB1 appeared to be normal in both red and white onions, but the transcription of CHS-A, which encodes chalcone synthase and is involved in the first step of the anthocyanin biosynthesis pathway, was inactivated in the white onions. Taken together, an aberrant AcMYB1 protein produced from the mutant allele might be responsible for the dominant white bulb color in onions.

MicroRNA164 Affects Plant Responses to UV Radiation in Perennial Ryegrass

Increasing the ultraviolet radiation (UV) level, particularly UV-B due to damage to the stratospheric ozone layer by human activities, has huge negative effects on plant and animal metabolism. As a widely grown cool-season forage grass and turfgrass in the world, perennial ryegrass (Lolium perenne) is UV-B-sensitive. To study the effects of miR164, a highly conserved microRNA in plants, on perennial ryegrass under UV stress, both OsmiR164a overexpression (OE164) and target mimicry (MIM164) transgenic perennial ryegrass plants were generated using agrobacterium-mediated transformation, and UV-B treatment (~600 μw cm-2) of 7 days was imposed. Morphological and physiological analysis showed that the miR164 gene affected perennial ryegrass UV tolerance negatively, demonstrated by the more scorching leaves, higher leaf electrolyte leakage, and lower relative water content in OE164 than the WT and MIM164 plants after UV stress. The increased UV sensitivity could be partially due to the reduction in antioxidative capacity and the accumulation of anthocyanins. This study indicated the potential of targeting miR164 and/or its targeted genes for the genetic manipulation of UV responses in forage grasses/turfgrasses; further research to reveal the molecular mechanism underlying how miR164 affects plant UV responses is needed.

Transcriptome Analysis on the Quality of Epimedium koreanum in Different Soil Moisture Conditions at Harvesting Stage

Epimedium koreanum is a traditional Chinese tonic herb. Its main medicinal components are secondary metabolites such as flavonoids and flavonol glycosides, but the biosynthetic mechanism is still unclear. Moisture conditions are a key environmental factor affecting E. koreanum medicinal components during harvesting. Different stages of E. koreanum under natural conditions after rainfall were selected to study changes in physiological properties, herb quality, and transcriptome. Malondialdehyde (MDA) content increased significantly in the D3 stage after rainfall, and protective enzyme levels also rose. Additionally, the flavonol glycoside content was relatively high. We sequenced the transcriptomes of D1, D3, and D9 (R) and identified differentially expressed genes (DEGs) related to flavonoid synthesis. This analysis allowed us to predict the roadmap and key genes involved in flavonoid biosynthesis for E. koreanum. These results suggest that the E. koreanum quality can be enhanced by natural drought conditions in the soil after precipitation during harvest. The harvesting period of E. koreanum is optimal when soil moisture naturally dries to a relative water content of 26% after precipitation. These conditions help E. koreanum tolerate a certain level of water scarcity, resulting in increased expression of flavonoid-related genes and ultimately enhancing the quality of the herb.

Integrated transcriptomic and metabolomic data reveal the cold stress responses molecular mechanisms of two coconut varieties

Among tropical fruit trees, coconut holds significant edible and economic importance. The natural growth of coconuts faces a challenge in the form of low temperatures, which is a crucial factor among adverse environmental stresses impacting their geographical distribution. Hence, it is essential to enhance our comprehension of the molecular mechanisms through which cold stress influences various coconut varieties. We employed analyses of leaf growth morphology and physiological traits to examine how coconuts respond to low temperatures over 2-hour, 8-hour, 2-day, and 7-day intervals. Additionally, we performed transcriptome and metabolome analyses to identify the molecular and physiological shifts in two coconut varieties displaying distinct sensitivities to the cold stress. As the length of cold stress extended, there was a prominent escalation within the soluble protein (SP), proline (Pro) concentrations, the activity of peroxidase (POD) and superoxide dismutase (SOD) in the leaves. Contrariwise, the activity of glutathione peroxidase (GSH) underwent a substantial reduction during this period. The widespread analysis of metabolome and transcriptome disclosed a nexus of genes and metabolites intricately cold stress were chiefly involved in pathways centered around amino acid, flavonoid, carbohydrate and lipid metabolism. We perceived several stress-responsive metabolites, such as flavonoids, carbohydrates, lipids, and amino acids, which unveiled considerably, lower in the genotype subtle to cold stress. Furthermore, we uncovered pivotal genes in the amino acid biosynthesis, antioxidant system and flavonoid biosynthesis pathway that presented down-regulation in coconut varieties sensitive to cold stress. This study broadly enriches our contemporary perception of the molecular machinery that contributes to altering levels of cold stress tolerance amid coconut genotypes. It also unlocks several unique prospects for exploration in the areas of breeding or engineering, aiming to identifying tolerant and/or sensitive coconut varieties encompassing multi-omics layers in response to cold stress conditions.

Chemical diversity of Brittonodoxa subpinnata, a Brazilian native species of moss

Plants should be probably thought of as the most formidable chemical laboratory that can be exploited for the production of an incredible number of molecules with remarkable structural and chemical diversity that cannot be matched by any synthetic libraries of small molecules. The bryophytes chemistry has been neglected for too long, but in the last ten years, this scenery is changing, with several studies being made using extracts from bryophytes, aimed at the characterization of interesting metabolites, with their metabolome screened. The main objective of this study was to analyze the metabolome of Brittonodoxa subpinnata, a native Brazilian moss species, which occurs in the two Brazilian hotspots. GC-MS and LC-MS2 were performed. All extracts were analyzed using the molecular networking approach. The four extracts of B. subpinnata (polar, non-polar, soluble, and insoluble) resulted in 928 features detected within the established parameters. 189 (20.4%) compounds were annotated, with sugars, fatty acids, flavonoids, and biflavonoids as the major constituents. Sucrose was the sugar with the highest quantity; palmitic acid the major fatty acid but with great presence of very long-chain fatty acids rarely found in higher plants, glycosylated flavonoids were the major flavonoids, and biflavonoids majorly composed by units of flavones and flavanones, exclusively found in the cell wall. Despite the high percentage, this work leaves a significant gap for future works using other structure elucidation techniques, such as NMR.

Common and specific genetic basis of metabolite-mediated drought responses in rice

Plants orchestrate drought responses at metabolic level but the genetic basis remains elusive in rice. In this study, 233 drought-responsive metabolites (DRMs) were quantified in a large rice population comprised of 510 diverse accessions at the reproductive stage. Large metabolic variations in drought responses were detected, and little correlation of metabolic levels between drought and normal conditions were observed. Interestingly, most of these DRMs could predict drought resistance in high accuracy. Genome-wide association study revealed 2522 significant association signals for 233 DRMs, and 98% (2471/2522) of the signals were co-localized with the association loci for drought-related phenotypic traits in the same population or the linkage-mapped QTLs for drought resistance in other populations. Totally, 10 candidate genes were efficiently identified for nine DRMs, seven of which harbored cis-eQTLs under drought condition. Based on comparative GWAS of common DRMs in rice and maize, representing irrigated and upland crops, we have identified three pairs of homologous genes associated with three DRMs between the two crops. Among the homologous genes, a transferase gene responsible for metabolic variation of N-feruloylputrescine was confirmed to confer enhanced drought resistance in rice. Our study provides not only genetic architecture of metabolic responses to drought stress in rice but also metabolic data resources to reveal the common and specific metabolite-mediated drought responses in different crops.

CRISPR/Cas9 mutated p-coumaroyl shikimate 3'-hydroxylase 3 gene in Populus tomentosa reveals lignin functioning on supporting tree upright

The lignin plays one of the most important roles in plant secondary metabolism. However, it is still unclear how lignin can contribute to the impressive height of wood growth. In this study, C3'H, a rate-limiting enzyme of the lignin pathway, was used as the target gene. C3'H3 was knocked out by CRISPR/Cas9 in Populus tomentosa. Compared with wild-type popular trees, c3'h3 mutants exhibited dwarf phenotypes, collapsed xylem vessels, weakened phloem thickening, decreased hydraulic conductivity and photosynthetic efficiency, and reduced auxin content, except for reduced total lignin content and significantly increased H-subunit lignin. In the c3'h3 mutant, the flavonoid biosynthesis genes CHS, CHI, F3H, DFR, ANR, and LAR were upregulated, and flavonoid metabolite accumulations were detected, indicating that decreasing the lignin biosynthesis pathway enhanced flavonoid metabolic flux. Furthermore, flavonoid metabolites, such as naringenin and hesperetin, were largely increased, while higher hesperetin content suppressed plant cell division. Thus, studying the c3'h3 mutant allows us to deduce that lignin deficiency suppresses tree growth and leads to the dwarf phenotype due to collapsed xylem and thickened phloem, limiting material exchanges and transport.

A Biostimulant Based on Silicon Chelates Enhances Growth and Modulates Physiological Responses of In-Vitro-Derived Strawberry Plants to In Vivo Conditions

The purpose was to assess the effects of a biostimulant based on silicon chelates in terms of alleviation of the impact of in vivo conditions on strawberry (Fragaria × ananassa cv. 'Solnechnaya polyanka') in-vitro-derived plants. As a source of silicon chelates, a mechanocomposite (MC) obtained through mechanochemical processing of rice husks and green tea was used. Root treatment of plants with 0.3 g L-1 of MC dissolved in tap water was performed at 2 weeks after planting. Control plants were watered with tap water. The greatest shoot height, number of roots per plant, root length, number of stolons per plant, daughter ramets per stolon, relative water content, cuticle thickness, and root and shoot biomasses were achieved with the MC supplementation. The improved parameters were associated with a higher silicon content of roots and shoots of the MC-treated plants. Leaf concentrations of hydrogen peroxide and abscisic acid were reduced by the MC. This effect was accompanied by enhanced activity of superoxide dismutase and catalase. The phenolic profile showed upregulation of p-hydroxybenzoic acid, vanillic acid, gallic acid, syringic acid, and ellagic acid derivative 2, while kaempferol rutinoside and catechins were downregulated. Thus, silicon chelates improve growth and trigger the physiological processes that enhance free-radical-scavenging activity in strawberry plants in vivo.

The endomembrane system: how does it contribute to plant secondary metabolism?

New organelle acquisition through neofunctionalization of the endomembrane system (ES) with respect to plant secondary metabolism is a key evolutionary strategy for plant adaptation, which is overlooked due to the complexity of angiosperms. Bryophytes produce a broad range of plant secondary metabolites (PSMs), and their simple cellular structures, including unique organelles, such as oil bodies (OBs), highlight them as suitable model to investigate the contribution of the ES to PSMs. In this opinion, we review latest findings on the contribution of the ES to PSM biosynthesis, with a specific focus on OBs, and propose that the ES provides organelles and trafficking routes for PSM biosynthesis, transportation, and storage. Therefore, future research on ES-derived organelles and trafficking routes will provide essential knowledge for synthetic applications.

Fusarium Head Blight Infection Induced Responses of Six Winter Wheat Varieties in Ascorbate-Glutathione Pathway, Photosynthetic Efficiency and Stress Hormones

Fusarium head blight (FHB) is one of the most studied fungal diseases of wheat, causing massive grain yield and quality losses. This study aimed to extend previous studies on the physiological and biochemical responses of winter wheat to FHB stress in a controlled environment by focusing on the ascorbate-glutathione pathway (AsA-GSH), photosynthetic efficiency, and stress hormone levels, thus providing insight into the possible interactions of different defense mechanisms during infection. The activity of AsA-GSH metabolism was increased in FHB resistant varieties, maintaining the redox state of spikes, and consequently preserving functional photosystem II. Furthermore, carotenoids (Car) were shown to be the major pigments in the photosystem assembly, as they decreased in FHB-stressed spikes of resistant and moderately resistant varieties, compared to controls. Car are also the substrate for the synthesis of abscisic acid (ABA), which acts as a fungal effector and its elevated content leads to increased FHB susceptibility in inoculated spikes. The results of this study contributed to the knowledge of FHB resistance mechanisms and can be used to improve the breeding of FHB resistant varieties, which is considered to be the most effective control measure.

Genome-wide identification, comparative analysis and functional roles in flavonoid biosynthesis of cytochrome P450 superfamily in pear (Pyrus spp.)

BACKGROUND

The cytochrome P450 (CYP) superfamily is the largest enzyme metabolism family in plants identified to date, and it is involved in many biological processes, including secondary metabolite biosynthesis, hormone metabolism and stress resistance. However, the P450 gene superfamily has not been well studied in pear (Pyrus spp.).

RESULTS

Here, the comprehensive identification and a comparative analysis of P450 superfamily members were conducted in cultivated and wild pear genomes. In total, 338, 299 and 419 P450 genes were identified in Chinese white pear, European pear and the wild pear, respectively. Based on the phylogenetic analyses, pear P450 genes were divided into ten clans, comprising 48 families. The motif and gene structure analyses further supported this classification. The expansion of the pear P450 gene family was attributed to whole-genome and single-gene duplication events. Several P450 gene clusters were detected, which have resulted from tandem and proximal duplications. Purifying selection was the major force imposed on the long-term evolution of P450 genes. Gene dosage balance, subfunctionalization and neofunctionalization jointly drove the retention and functional diversification of P450 gene pairs. Based on the association analysis between transcriptome expression profiles and flavonoid content during fruit development, three candidate genes were identified as being closely associated with the flavonoid biosynthesis, and the expression of one gene was further verified using qRT-PCR and its function was validated through transient transformation in pear fruit.

CONCLUSIONS

The study results provide insights into the evolution and biological functions of P450 genes in pear.

Reactive Oxygen Species in Drought-Induced Stomatal Closure: The Potential Roles of NPR1

Stomatal closure is a vital, adaptive mechanism that plants utilize to minimize water loss and withstand drought conditions. We will briefly review the pathway triggered by drought that governs stomatal closure, with specific focuses on salicylic acid (SA) and reactive oxygen species (ROS). We propose that the non-expressor of PR Gene 1 (NPR1), a protein that protects plants during pathogen infections, also responds to SA during drought to sustain ROS levels and prevent ROS-induced cell death. We will examine the evidence underpinning this hypothesis and discuss potential strategies for its practical implementation.

Physiological response and molecular regulatory mechanism reveal a positive role of nitric oxide and hydrogen sulfide applications in salt tolerance of Cyclocarya paliurus

As a multifunctional tree species, Cyclocarya paliurus leaves are rich in bioactive substances with precious healthy values. To meet the huge requirement of C. paliurus leaf production, sites with some environmental stresses would be potential land for developing its plantations due to the limitation of land resources in China. Nitric oxide (NO) and hydrogen sulfide (H2S) are common gas messengers used to alleviate abiotic stress damage, whereas the mechanism of these messengers in regulating salt resistance of C. paliurus still remains unclear. We performed a comprehensive study to reveal the physiological response and molecular regulatory mechanism of C. paliurus seedlings to the application of exogenous NO and H2S under salt stress. The results showed that the application of sodium hydrosulfide (NaHS) and sodium nitroprusside (SNP) not only maintained the photosynthetic capacity and reduced the loss of leaf biomass, but also promoted endogenous NO synthesis and reduced oxidative damage by activating antioxidant enzyme activity and increasing the content of soluble protein and flavonoids. Moreover, transcriptome and metabolome analysis indicated the expression of genes encoding phenylalanine ammonia lyase (PAL), cytochromeP450 (CYP), chalcone synthase (CHS), dihydroflavonol 4-reductase (DFR) and flavonol synthase (FLS) in flavonoid biosynthesis pathway was all up-regulated by the application of NO and H2S. Meanwhile, 15 transcriptional factors (TFs) such as WRKY, ERF, bHLH and HY5 induced by NO were found to regulated the activities of several key enzymes in flavonoid biosynthesis pathway under salt stress, via the constructed co-expression network. Our findings revealed the underlying mechanism of NO and H2S to alleviate salt stress and regulate flavonoid biosynthesis, which provides a theoretical basis for establishing C. paliurus plantations in the salt stress areas.

Evaluating the antioxidative defense response of selected indoor plants against benzene and formaldehyde

Volatile organic compounds (VOCs) such as formaldehyde and benzene are among the key contributors to indoor air pollution. The current situation of environmental pollution is alarming, especially indoor air pollution is becoming a challenge as affecting plants and humans. VOCs are known to adversely affect indoor plants by causing necrosis and chlorosis. In order to withstand these organic pollutants, plants are naturally equipped with an antioxidative defense system. The current research study aimed to evaluate the combined effect of formaldehyde and benzene on the antioxidative response of selected indoor C3 plants including Chlorophytum comosum, Dracaena mysore, and Ficus longifolia. After the combined application of different levels (0, 0; 2, 2; 2, 4; 4, 2; and 4, 4 ppm) of benzene and formaldehyde respectively, in an airtight glass chamber, the enzymatic and non-enzymatic antioxidants were analyzed. Analysis of total phenolics showed a significant increase (10.72 mg GAE/g) in F. longifolia; C. comosum (9.20 mg GAE/g); and D. mysore (8.74 mg GAE/g) compared to their respective controls as 3.76, 5.39, and 6.07 mg GAE/g. Total flavonoids (724 µg/g) were reported in control plants of F. longifolia which were increased to 1545.72 µg/g from 724 µg/g (in control) followed by 322.66 µg/g in D. mysore (control having 167.11 µg/g). Total carotenoid content also increased in D. mysore (0.67 mg/g) followed by C. comosum (0.63 mg/g) in response to increasing the combined dose compared to their control plants having 0.62 and 0.24 mg/g content. The highest proline content was exhibited by D. mysore (3.66 μg/g) as compared to its respective control plant (1.54 μg/g) under a 4 ppm dose of benzene and formaldehyde. A significant increase in enzymatic antioxidants including total antioxidants (87.89%), catalase (59.21 U/mg of protein), and guaiacol peroxidase (52.16 U/mg of protein) was observed in the D. mysore plant under a combined dose of benzene (2 ppm) and formaldehyde (4 ppm) with respect to their controls. Although experimental indoor plants have been reported to metabolize indoor pollutants, the current findings indicate that the combined application of benzene and formaldehyde is also affecting the physiology of indoor plants as well.

How do barley plants with impaired photosynthetic light acclimation survive under high-light stress?

MAIN CONCLUSION

WHIRLY1 deficient barley plants surviving growth at high irradiance displayed increased non-radiative energy dissipation, enhanced contents of zeaxanthin and the flavonoid lutonarin, but no changes in α-tocopherol nor glutathione. Plants are able to acclimate to environmental conditions to optimize their functions. With the exception of obligate shade plants, they can adjust their photosynthetic apparatus and the morphology and anatomy of their leaves to irradiance. Barley (Hordeum vulgare L., cv. Golden Promise) plants with reduced abundance of the protein WHIRLY1 were recently shown to be unable to acclimatise important components of the photosynthetic apparatus to high light. Nevertheless, these plants did not show symptoms of photoinhibition. High-light (HL) grown WHIRLY1 knockdown plants showed clear signs of exposure to excessive irradiance such as a low epoxidation state of the violaxanthin cycle pigments and an early light saturation of electron transport. These responses were underlined by a very large xanthophyll cycle pool size and by an increased number of plastoglobules. Whereas zeaxanthin increased with HL stress, α-tocopherol, which is another lipophilic antioxidant, showed no response to excessive light. Also the content of the hydrophilic antioxidant glutathione showed no increase in W1 plants as compared to the wild type, whereas the flavone lutonarin was induced in W1 plants. HPLC analysis of removed epidermal tissue indicated that the largest part of lutonarin was presumably located in the mesophyll. Since lutonarin is a better antioxidant than saponarin, the major flavone present in barley leaves, it is concluded that lutonarin accumulated as a response to oxidative stress. It is also concluded that zeaxanthin and lutonarin may have served as antioxidants in the WHIRLY1 knockdown plants, contributing to their survival in HL despite their restricted HL acclimation.

Genome-wide identification of bZIP transcription factor family in Artemisia annua, its transcriptional profiling and regulatory role in phenylpropanoid metabolism under different light conditions

The basic leucine zipper (bZIP) protein transcription factors are known to modulate development, plant growth, metabolic response, and resistance to several biotic and abiotic stressors and have been widely studied in the model plant Arabidopsis thaliana. However, no comprehensive information about the bZIP transcription factor family in Artemisia annua has been explored to date. In this genome-wide study, we identified 61 bZIP TFs after removing false positives and incomplete sequences from Artemisia annua. Seven highly expressed homolog AabZIP TF genes under UV-B and differential light conditions in different tissues were identified from the publicly available microarray dataset as having their cis-regulatory elements involved in, flavonoids biosynthesis, seed-specific gene regulation, stress responses, and metabolic regulation. In-silico analysis and electrophoretic mobility shift assay (EMSA) confirmed the interaction of AabZIP19 TF over the AaPAL1 promoter in order to regulate the phenolics and flavonoid biosynthesis via the phenylpropanoid pathway. Further, RT-PCR analysis has been carried out to validate the transcript levels of selected AabZIP genes under white light, red light, blue light (45 min), and UV-B exposure (12 and 24 h). These genes have their highest expression levels under UV-B and blue light exposure, in contrast with white light. Therefore, the detection of ROS through staining confirms the accumulation of superoxide radicals and H2O2, and in addition to reducing ROS accumulation under UV-B and blue light irradiation, total phenols and flavonoids are significantly enhanced. This study laid the groundwork for deciphering the possible role of AabZIP TFs under different light stress-responsive conditions and in the regulation of secondary metabolism.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01338-0.

Advances in the study of the function and mechanism of the action of flavonoids in plants under environmental stresses

MAIN CONCLUSION

This review summarizes the anti-stress effects of flavonoids in plants and highlights its role in the regulation of polar auxin transport and free radical scavenging mechanism. As secondary metabolites widely present in plants, flavonoids play a vital function in plant growth, but also in resistance to stresses. This review introduces the classification, structure and synthetic pathways of flavonoids. The effects of flavonoids in plant stress resistance were enumerated, and the mechanism of flavonoids in plant stress resistance was discussed in detail. It is clarified that plants under stress accumulate flavonoids by regulating the expression of flavonoid synthase genes. It was also determined that the synthesized flavonoids are transported in plants through three pathways: membrane transport proteins, vesicles, and bound to glutathione S-transferase (GST). At the same time, the paper explores that flavonoids regulate polar auxin transport (PAT) by acting on the auxin export carrier PIN-FORMED (PIN) in the form of ATP-binding cassette subfamily B/P-glycoprotein (ABCB/PGP) transporter, which can help plants to respond in a more dominant form to stress. We have demonstrated that the number and location of hydroxyl groups in the structure of flavonoids can determine their free radical scavenging ability and also elucidated the mechanism by which flavonoids exert free radical removal in cells. We also identified flavonoids as signaling molecules to promote rhizobial nodulation and colonization of arbuscular mycorrhizal fungi (AMF) to enhance plant-microbial symbiosis in defense to stresses. Given all this knowledge, we can foresee that the in-depth study of flavonoids will be an essential way to reveal plant tolerance and enhance plant stress resistance.

Potentiating Biosynthesis of Alkaloids and Polyphenolic Substances in Catharanthus roseus Plant Using ĸ-Carrageenan

Catharanthus roseus is a medicinal plant that produces indole alkaloids, which are utilized in anticancer therapy. Vinblastine and vincristine, two commercially important antineoplastic alkaloids, are mostly found in the leaves of Catharanthus roseus. ĸ-carrageenan has been proven as plant growth promoting substance for a number of medicinal and agricultural plants. Considering the importance of ĸ-carrageenan as a promoter of plant growth and phytochemical constituents, especially alkaloids production in Catharanthus roseus, an experiment was carried out to explore the effect of ĸ-carrageenan on the plant growth, phytochemicals content, pigments content, and production of antitumor alkaloids in Catharanthus roseus after planting. Foliar application of ĸ-carrageenan (at 0, 400, 600 and 800 ppm) significantly improved the performance of Catharanthus roseus. Phytochemical analysis involved determining the amount of total phenolics (TP), flavonoids (F), free amino acids (FAA), alkaloids (TAC) and pigments contents by spectrophotometer, minerals by ICP, amino acids, phenolic compounds and alkaloids (Vincamine, Catharanthine, Vincracine (Vincristine), and vinblastine) analysis uses HPLC. The results indicated that all examined ĸ-carrageenan treatments led to a significant (p ≤ 0.05) increase in growth parameters compared to the untreated plants. Phytochemical examination indicates that the spray of ĸ-carrageenan at 800 mg L^-1 increased the yield of alkaloids (Vincamine, Catharanthine and Vincracine (Vincristine)) by 41.85 μg/g DW, total phenolic compounds by 3948.6 μg gallic/g FW, the content of flavonoids 951.3 μg quercetin /g FW and carotenoids content 32.97 mg/g FW as compared to the control. An amount of 400 ppm ĸ-carrageenan treatment gave the best contents of FAA, Chl a, Chl b and anthocyanin. The element content of K, Ca, Cu, Zn and Se increased by treatments. Amino acids constituents and phenolics compounds contents were altered by ĸ-carrageenan.

Physiological and transcriptome analysis of Dendrobium officinale under low nitrogen stress

Nitrogen (N) is the main nutrient of plants, and low nitrogen usually affects plant growth and crop yield. The traditional Chinese herbal medicine Dendrobium officinale Kimura et. Migo is a typical low nitrogen-tolerant plant, and its mechanism in response to low nitrogen stress has not previously been reported. In this study, physiological measurements and RNA-Seq analysis were used to analyse the physiological changes and molecular responses of D. officinale under different nitrogen concentrations. The results showed that under low nitrogen levels, the growth, photosynthesis and superoxide dismutase activity were found to be significantly inhibited, while the activities of peroxidase and catalase, the content of polysaccharides and flavonoids significantly increased. Differentially expressed genes (DEGs) analysis showed that nitrogen and carbon metabolisms, transcriptional regulation, antioxidative stress, secondary metabolite synthesis and signal transduction all made a big difference in low nitrogen stress. Therefore, copious polysaccharide accumulation, efficient assimilation and recycling of nitrogen, as well as rich antioxidant components play critical roles. This study is helpful for understanding the response mechanism of D. officinale to low nitrogen levels, which might provide good guidance for practical production of high quality D. officinale .

Transcriptome and Low-Affinity Sodium Transport Analysis Reveals Salt Tolerance Variations between Two Poplar Trees

Salinity stress severely hampers plant growth and productivity. How to improve plants’ salt tolerance is an urgent issue. However, the molecular basis of plant resistance to salinity still remains unclear. In this study, we used two poplar species with different salt sensitivities to conduct RNA-sequencing and physiological and pharmacological analyses; the aim is to study the transcriptional profiles and ionic transport characteristics in the roots of the two Populus subjected to salt stress under hydroponic culture conditions. Our results show that numerous genes related to energy metabolism were highly expressed in Populus alba relative to Populus russkii, which activates vigorous metabolic processes and energy reserves for initiating a set of defense responses when suffering from salinity stress. Moreover, we found the capacity of Na+ transportation by the P. alba high-affinity K+ transporter1;2 (HKT1;2) was superior to that of P. russkii under salt stress, which enables P. alba to efficiently recycle xylem-loaded Na+ and to maintain shoot K+/Na+ homeostasis. Furthermore, the genes involved in the synthesis of ethylene and abscisic acid were up-regulated in P. alba but downregulated in P. russkii under salt stress. In P. alba, the gibberellin inactivation and auxin signaling genes with steady high transcriptions, several antioxidant enzymes activities (such as peroxidase [POD], ascorbate peroxidase [APX], and glutathione reductase [GR]), and glycine-betaine content were significantly increased under salt stress. These factors altogether confer P. alba a higher resistance to salinity, achieving a more efficient coordination between growth modulation and defense response. Our research provides significant evidence to improve the salt tolerance of crops or woody plants.

Genetic Analyses of Seed Longevity in Capsicum annuum L. in Cold Storage Conditions

Seed longevity is the most important trait in the genebank management system. No seed can remain infinitely viable. There are 1241 accessions of Capsicum annuum L. available at the German Federal ex situ genebank at IPK Gatersleben. C. annuum (Capsicum) is the most economically important species of the genus Capsicum. So far, there is no report that has addressed the genetic basis of seed longevity in Capsicum. Here, we convened a total of 1152 Capsicum accessions that were deposited in Gatersleben over forty years (from 1976 to 2017) and assessed their longevity by analyzing the standard germination percentage after 5-40 years of storage at -15/-18 °C. These data were used to determine the genetic causes of seed longevity, along with 23,462 single nucleotide polymorphism (SNP) markers covering all of the 12 Capsicum chromosomes. Using the association-mapping approach, we identified a total of 224 marker trait associations (MTAs) (34, 25, 31, 35, 39, 7, 21 and 32 MTAs after 5-, 10-, 15-, 20-, 25-, 30-, 35- and 40-year storage intervals) on all the Capsicum chromosomes. Several candidate genes were identified using the blast analysis of SNPs, and these candidate genes are discussed.

Use of a Biostimulant to Mitigate the Effects of Excess Salinity in Soil and Irrigation Water in Tomato Plants

Global warming is linked to progressive soil salinisation, which reduces crop yields, especially in irrigated farmland on arid and semiarid regions. Therefore, it is necessary to apply sustainable and effective solutions that contribute to enhanced crop salt tolerance. In the present study, we tested the effects of a commercial biostimulant (BALOX^®) containing glycine betaine (GB) and polyphenols on the activation of salinity defense mechanisms in tomato. The evaluation of different biometric parameters and the quantification of biochemical markers related to particular stress responses (osmolytes, cations, anions, oxidative stress indicators, and antioxidant enzymes and compounds) was carried out at two phenological stages (vegetative growth and the beginning of reproductive development) and under different salinity conditions (saline and non-saline soil, and irrigation water), using two formulations (different GB concentrations) and two doses of the biostimulant. Once the experiments were completed, the statistical analysis revealed that both formulations and doses of the biostimulant produced very similar effects. The application of BALOX^® improved plant growth and photosynthesis and assisted osmotic adjustment in root and leaf cells. The biostimulant effects are mediated by the control of ion transport, reducing the uptake of toxic Na⁺ and Cl^- ions and favoring the accumulation of beneficial K⁺ and Ca²⁺ cations, and a significant increase in leaf sugar and GB contents. BALOX^® significantly reduced salt-induced oxidative stress and its harmful effects, as evidenced by a decrease in the concentration of oxidative stress biomarkers, such as malondialdehyde and oxygen peroxide, which was accompanied by the reduction of proline and antioxidant compound contents and the specific activity of antioxidant enzymes with respect to the non-treated plants.

Fe (III)-Mediated Antioxidant Response of the Acidotolerant Microalga Coccomyxa onubensis

Coccomyxa onubensis (C. onubensis) is an acidotolerant microalga isolated from Tinto River (Huelva), which contains high levels of metal cations in solution, mainly Fe (II) and (III), and Cu (II). Fe is more bioavailable at low pH, mainly because Fe (II) and Fe (III) are far more soluble, especially Fe (III). For this reason, this study aims to evaluate both physiological and biochemical responses of C. onubensis when subjected to Fe (III)-induced stress. Changes in growth, photosynthetic viability and antioxidant responses to the induced oxidative stress were determined. The results obtained suggest that the addition of moderate Fe (III) levels to C. onubensis cultures results in improved growth and photosynthetic viability. Increases in the intracellular levels of the enzyme superoxide dismutase (SOD) and flavonoids, used as antioxidant response biomarkers, a point at Fe (III)-mediated oxidative stress induction. The apparent decrease in the content of other phenolic molecules and polyunsaturated fatty acids might be understood as a sign of antioxidant molecules' involvement in reactive oxygen species (ROS) scavenging. In conclusion, a noticeable antioxidant capacity displayed by C. onubensis allows the use of moderate Fe (III) levels to trigger the accumulation of valuable antioxidant molecules, allowing the production of cell extracts with potential anti-inflammatory activity.

Inductive role of the brown alga Sargassum polycystum on growth and biosynthesis of imperative metabolites and antioxidants of two crop plants

The potential of macroalgae as biostimulants in agriculture was proved worthy. Vicia faba and Helianthus annuus are socioeconomic crops owing to their increasing demand worldwide. In this work, we investigated the energetic role of seed presoaking and irrigation by the brown seaweed, Sargassum polycystum aqueous extract (SAE) on certain germination and growth traits, photosynthetic pigments, carbohydrates, phenolics, flavonoids, and the total antioxidant activity. Compared to the control plants, our consequences revealed that seeds that received the SAE improved all the germination and growth criteria for both crop plants. Furthermore, the SAE significantly increased the carotenoids, total photosynthetic pigments, and total carbohydrates by (14%, 7%, and 41%) for V. faba and (17%, 17%, and 38%) for H. annuus, respectively. Phenolics and flavonoids were significantly induced in Vicia but slightly promoted in Helianthu plants, whereas the total antioxidant activity in both crops non significantly elevated. Even though The NPK contents were significantly stimulated by the SAE in Vicia plants, the effect was different in Helianthus, where only nitrogen content was significantly enhanced, whereas phosphorus and potassium showed little enhancement. Thus, the SAE treatment is one of the superlative sustainable strategies for food, feed, and as excellent plant conditioner.

Deciphering salt tolerance in tetraploid honeysuckle (Lonicera japonica Thunb.) from ion homeostasis, water balance and antioxidant defense

Polyploid plants are usually salt tolerant, but the underlying mechanisms remain fragmental. This study aimed to dissect salt resistance of tetraploid honeysuckle (Lonicera japonica Thunb.) from ion balance, osmotic adjustment and antioxidant defense by contrasting with its autodiploid through pot experiments. Less salt-induced reduction in leaf and root biomass confirmed higher tolerance in tetraploid honeysuckle, and moreover, its greater stability of photosynthetic apparatus was verified by mild influence on delayed chlorophyll fluorescence transients. Compared with the diploid, greater root Na⁺ exclusion helped alleviate salt-induced decrease in leaf K⁺/Na⁺ for maintaining ion balance in tetraploid honeysuckle, and relied on Na⁺/H⁺ antiporter activity, because their difference of root Na⁺ exclusion disappeared after applying a specific inhibitor of Na⁺/H⁺ antiporter. Lower reduction in leaf relative water content suggested higher tolerance to osmotic pressure in tetraploid honeysuckle under salt stress, which hardly resulted from osmotic adjustment given the similar decrease extent of leaf osmotic potential with that in the diploid. In contrast to significant elevated leaf lipid peroxidation and superoxide dismutase and ascorbate peroxidase activities in the diploid, no obvious changes in them suggested that tetraploid honeysuckle never suffered salt-induced oxidative stress. According to more accumulated leaf chlorogenic acid and phenolics and greater elevated leaf phenylalanine ammonia-lyase activity and transcription, leaf phenolic synthesis was enhanced greater in tetraploid honeysuckle upon salt stress, which might serve to prevent oxidative threat by consuming reducing power. In conclusion, polyploidy enhanced salt tolerance in honeysuckle by maintaining ion homeostasis and water balance and preventing oxidative stress.

Friends in Arms: Flavonoids and the Auxin/Cytokinin Balance in Terrestrialization

Land plants survive the challenges of new environments by evolving mechanisms that protect them from excess irradiation, nutrient deficiency, and temperature and water availability fluctuations. One such evolved mechanism is the regulation of the shoot/root growth ratio in response to water and nutrient availability by balancing the actions of the hormones auxin and cytokinin. Plant terrestrialization co-occurred with a dramatic expansion in secondary metabolism, particularly with the evolution and establishment of the flavonoid biosynthetic pathway. Flavonoid biosynthesis is responsive to a wide range of stresses, and the numerous synthesized flavonoid species offer two main evolutionary advantages to land plants. First, flavonoids are antioxidants and thus defend plants against those adverse conditions that lead to the overproduction of reactive oxygen species. Second, flavonoids aid in protecting plants against water and nutrient deficiency by modulating root development and establishing symbiotic relations with beneficial soil fungi and bacteria. Here, we review different aspects of the relationships between the auxin/cytokinin module and flavonoids. The current body of knowledge suggests that whereas both auxin and cytokinin regulate flavonoid biosynthesis, flavonoids act to fine-tune only auxin, which in turn regulates cytokinin action. This conclusion agrees with the established master regulatory function of auxin in controlling the shoot/root growth ratio.

Transgressive Biochemical Response to Water Stress in Interspecific Eggplant Hybrids

In a climate change scenario, crop tolerance to drought must be urgently improved, as it represents an increasingly critical stress reducing agricultural yields worldwide. Although most crops are relatively sensitive to water stress, many of their wild relatives are more tolerant and may be used to improve drought tolerance in our crops. In this study, the response to drought of eggplant (Solanum melongena), its close wild relatives S. insanum and S. incanum and their interspecific hybrids with S. melongena was assessed. The plants were subjected to two treatments for 18 days: control, with irrigation every four days, and drought, with complete interruption of irrigation. Morphological and biomass traits were measured, and physiological and biochemical responses were analysed using stress biomarkers such as proline, flavonoids, and total phenolic compounds. Oxidative stress was quantified by measuring malondialdehyde (MDA) content. As a result of the drought treatment, plant development and tissue water content were seriously affected. Generally, water deficit also caused significant increases in MDA, proline, flavonoids, and total phenolics compounds. Our results comparing parental accessions reveal a better response to drought in one of the S. insanum accessions. The hybrid between S. melongena and S. incanum displayed a better response than the other hybrids and even its parents. The results obtained here might be helpful for future eggplant breeding programmes aimed at improving drought tolerance.

Transcriptomic Analysis Provides Insight into the ROS Scavenging System and Regulatory Mechanisms in Atriplex canescens Response to Salinity

Atriplex canescens is a representative halophyte with excellent tolerance to salt. Previous studies have revealed certain physiological mechanisms and detected functional genes associated with salt tolerance. However, knowledge on the ROS scavenging system and regulatory mechanisms in this species when adapting to salinity is limited. Therefore, this study further analyzed the transcriptional changes in genes related to the ROS scavenging system and important regulatory mechanisms in A. canescens under saline conditions using our previous RNA sequencing data. The Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway annotation revealed that the differentially expressed genes (DEGs) were highly enriched in signal transduction- and reactive oxygen species-related biological processes, including "response to oxidative stress", "oxidoreductase activity", "protein kinase activity", "transcription factor activity", and "plant hormone signal transduction". Further analyses suggested that the transcription abundance of many genes involved in SOD, the AsA-GSH cycle, the GPX pathway, PrxR/Trx, and the flavonoid biosynthesis pathway were obviously enhanced. These pathways are favorable for scavenging excessive ROS induced by salt and maintaining the integrity of the cell membrane. Meanwhile, many vital transcription factor genes (WRKY, MYB, ZF, HSF, DREB, and NAC) exhibited increased transcripts, which is conducive to dealing with saline conditions by regulating downstream salt-responsive genes. Furthermore, a larger number of genes encoding protein kinases (RLK, CDPK, MAPK, and CTR1) were significantly induced by saline conditions, which is beneficial to the reception/transduction of salt-related signals. This study describes the abundant genetic resources for enhancing the salt tolerance in salt-sensitive plants, especially in forages and crops.

Integrated transcriptomic and metabolomic analyses of the molecular mechanisms of two highland barley genotypes with pyroxsulam responses

Highland barley is one of the few crops that can be grown at high elevations, making it a key resource within the Tibet Plateau. Weeds are a significant threat to highland barley production, and new herbicides and tolerant barley varieties are needed to control this ever-growing problem. A better understanding of existing herbicide resistance mechanisms is therefore needed. In this study, transcriptomic and metabolomic analyses were used to identify molecular and physiological changes in two highland barley genotypes with differing sensitivities to the herbicide pyroxsulam. We identified several stress-responsive metabolites, including flavonoids and antioxidants, which accumulated to significantly higher levels in the pyroxsulam-resistant genotype. Additionally, we found key genes in both the flavonoid biosynthesis pathway and the antioxidant system that were up-regulated in pyroxsulam-resistant barley. This work significantly expands on the current understanding of the molecular mechanisms underlying differing pyroxsulam tolerance among barley genotypes and provides several new avenues to explore for breeding or engineering tolerant barley.

Flavonoids Are Intra- and Inter-Kingdom Modulator Signals

Flavonoids are a broad class of secondary metabolites with multifaceted functionalities for plant homeostasis and are involved in facing both biotic and abiotic stresses to sustain plant growth and health. Furthermore, they were discovered as mediators of plant networking with the surrounding environment, showing a surprising ability to perform as signaling compounds for a multitrophic inter-kingdom level of communication that influences the plant host at the phytobiome scale. Flavonoids orchestrate plant-neighboring plant allelopathic interactions, recruit beneficial bacteria and mycorrhizal fungi, counteract pathogen outbreak, influence soil microbiome and affect plant physiology to improve its resilience to fluctuating environmental conditions. This review focuses on the diversified spectrum of flavonoid functions in plants under a variety of stresses in the modulation of plant morphogenesis in response to environmental clues, as well as their role as inter-kingdom signaling molecules with micro- and macroorganisms. Regarding the latter, the review addresses flavonoids as key phytochemicals in the human diet, considering their abundance in fruits and edible plants. Recent evidence highlights their role as nutraceuticals, probiotics and as promising new drugs for the treatment of several pathologies.

Dynamic Changes in the Antioxidative Defense System in the Tea Plant Reveal the Photoprotection-Mediated Temporal Accumulation of Flavonoids under Full Sunlight Exposure

To reveal the mechanisms underlying how light affects flavonoid metabolism and the potential role of flavonoids in protecting against photooxidative stress in tea leaves, tea plants adapted to low-light conditions were exposed to full sunlight over 48 h. There was an increase in the activities of catalase (CAT) and superoxide dismutase (SOD) as well as greater accumulation of reactive oxygen species, lutein, tocopherols, ascorbate and malondialdehyde, suggestive of a time-dependent response to photooxidative stress in tea leaves. Analysis of the time dependency of each element of the antioxidant system indicated that carotenoids and tocopherols exhibited the fastest response to light stress (within 3 h), followed by SOD, CAT and catechin, which peaked at 24 h. Meanwhile, flavonols, vitamin C and glutathione showed the slowest response. Subsequent identification of the main phytochemicals involved in protecting against oxidative stress using untargeted metabolomics revealed a fast and initial accumulation of nonesterified catechins that preceded the increase in flavonol glycosides and catechin esters. Gene expression analysis suggested that the light-induced accumulation of flavonoids was highly associated with the gene encoding flavonol synthase. Ultraviolet B (UV-B) irradiation further validated the time-dependent and collaborative effects of flavonoids in photoprotection in tea plants. Intriguingly, the dynamics of the metabolic response are highly distinct from those reported for Arabidopsis, suggesting that the response to light stress is not conserved across plants. This study additionally provides new insights into the functional role of flavonoids in preventing photooxidative stress and may contribute to further improving tea quality through the control of light intensity.

Altering the balance between AOX1A and NDB2 expression affects a common set of transcripts in Arabidopsis

Stress-responsive components of the mitochondrial alternative electron transport pathway have the capacity to improve tolerance of plants to abiotic stress, particularly the alternative oxidase AOX1A but also external NAD(P)H dehydrogenases such as NDB2, in Arabidopsis. NDB2 and AOX1A can cooperate to entirely circumvent the classical electron transport chain in Arabidopsis mitochondria. Overexpression of AOX1A or NDB2 alone can have slightly negative impacts on plant growth under optimal conditions, while simultaneous overexpression of NDB2 and AOX1A can reverse these phenotypic effects. We have taken a global transcriptomic approach to better understand the molecular shifts that occur due to overexpression of AOX1A alone and with concomitant overexpression of NDB2. Of the transcripts that were significantly up- or down- regulated in the AOX1A overexpression line compared to wild type (410 and 408, respectively), the majority (372 and 337, respectively) reverted to wild type levels in the dual overexpression line. Several mechanisms for the AOX1A overexpression phenotype are proposed based on the functional classification of these 709 genes, which can be used to guide future experiments. Only 28 genes were uniquely up- or down-regulated when NDB2 was overexpressed in the AOX1A overexpression line. On the other hand, many unique genes were deregulated in the NDB2 knockout line. Furthermore, several changes in transcript abundance seen in the NDB2 knockout line were consistent with changes in the AOX1A overexpression line. The results suggest that an imbalance in AOX1A:NDB2 protein levels caused by under- or over-expression of either component, triggers a common set of transcriptional responses that may be important in mitochondrial redox regulation. The most significant changes were transcripts associated with photosynthesis, secondary metabolism and oxidative stress responses.

Flavonoids and Devosia sp SL43 cell-free supernatant increase early plant growth under salt stress and optimal growth conditions

Salt stress is a major threat to modern agriculture, significantly affecting plant growth and yield, and causing substantial economic losses. At this crucial time of increasing climate change conditions, soil salinity will continue to develop and become an even more serious challenge to crop agriculture. Hence, there is a pressing need for sustainable techniques in agricultural production that could meet the dual challenges of crop productivity and environmental instability. The use of biostimulants in agricultural production has greatly influenced plant health and global food production. In particular, the application of bioactive materials produced by beneficial microbes is becoming a common practice in agriculture and provides numerous benefits to plant growth and resistance to stressful conditions. In this research two biostimulants; a type of plant secondary metabolite (flavonoids) and a microbe-based material (CFS: Cell-Free Supernatant) containing active compounds secreted by a novel bacterial strain isolated from Amphecarpaea bracteata root nodules (Devosia sp - SL43), have been utilized to improve the growth and stress resistance of two major oil seed crops; canola and soybean, under optimal and salt stress conditions. Our findings suggested significant improvements in crop growth of canola and soybean following the application of both biostimulants. Under optimal growth conditions, soybean growth was significantly affected by foliar spray of flavonoids with increases in shoot fresh and dry weight, and leaf area, by 91, 99.5, and 73%, respectively. However, soybean growth was unaffected by flavonoids under salt stress. In contrast, CFS with a meaningful capacity to mitigate the negative effects of salinity stress improved soybean shoot fresh biomass, dry biomass, and leaf area by 128, 163 and 194%, respectively, under salt stress conditions. Canola was less responsive to both biostimulants, except for canola root variables which were substantially improved by flavonoid spray. Since this was the first assessment of these materials as foliar sprays, we strongly encourage further experimentation to confirm the findings reported here and to determine the full range of applicability of each of these potential technologies.

Integrated metabolomic and transcriptomic analyses reveal different metabolite biosynthesis profiles of Juglans mandshurica in shade

Light is not only a very important source of energy for the normal growth and development of plants, but also a regulator of many development and metabolic processes. The mechanism of plant growth and development under low light conditions is an important scientific question. With the promulgation of the law to stop natural forest cutting, understory regeneration is an important method for artificial forest afforestation. Here, the growth and physiological indexes of Juglans mandshurica, an important hardwood species in Northeast China, were measured under different shade treatments. In addition, transcriptome and metabolome were compared to analyze the molecular mechanism of shade tolerance in J. mandshurica. The results showed that the seedling height of the shade treatment group was significantly higher than that of the control group, and the 50% light (L50) treatment was the highest. Compared with the control group, the contents of gibberellin, abscisic acid, brassinolide, chlorophyll a, and chlorophyll b in all shade treatments were significantly higher. However, the net photosynthetic rate and water use efficiency decreased with increasing shade. Furthermore, the transcriptome identified thousands of differentially expressed genes in three samples. Using enrichment analysis, we found that most of the differentially expressed genes were enriched in photosynthesis, plant hormone signal transduction and chlorophyll synthesis pathways, and the expression levels of many genes encoding transcription factors were also changed. In addition, analysis of differentially accumulated metabolites showed that a total of 470 differential metabolites were identified, and flavonoids were the major differential metabolites of J. mandshurica under light stress. These results improved our understanding of the molecular mechanism and metabolite accumulation under light stress in J. mandshurica.

Reactive oxygen species in plants: an invincible fulcrum for biotic stress mitigation

Climate change-associated environmental vagaries have amplified the incidence of pests and pathogens on plants, thus imparting the increased quest for management strategies. Plants respond to stresses through intricate signaling networks that regulate diverse cellular mechanisms. Reactive oxygen species (ROS) are cardinal towards the maintenance of normal plant activities as well as improving stress management. Plants that exhibit a fine balance between ROS levels and its management apparently mitigate stresses better. There have been very many compendiums on signaling and management of ROS during several abiotic stresses. However, expansion of knowledge related to ROS induction and homeostasis during biotic stresses is pertinent. Hence, considering its importance, we provide insights in this review on how plants signal and manage ROS upon an oxidative burst during their interaction with pathogens and herbivores. Substantial degree of molecular changes and pivotal roles of ROS have been detected during phyto-pathogen/herbivore interactions, opening novel platforms to understand signaling/management of events under varied biotic stresses. It is interesting to know that, though plants react to biotic stresses through oxidative burst, receptors and elicitors involved in the signal transduction differ across stresses. The review provides explicit details about the specific signaling of ROS production in plants under pathogen and herbivore attack. Furthermore, we also provide an update about tackling the accumulated ROS under biotic stresses as another pivotal step. ROS signaling and homeostasis can be exploited as critical players and a fulcrum to tackle biotic stresses, thus paving the way for futuristic combinatorial stress management strategies. KEY POINTS: • The review is a comprehension of redox signaling and management in plants during herbivory and pathogen infection • Reactive oxygen species (ROS) is an important factor during normal plant activities as well as in their response to stresses. Diverse modes of ROS signaling and management have been observed during both biotic stresses independently • Exploration of plant biology in multi-stress resistant plants like the crop wild relatives could pave the way for combinatorial management of stress for a better tomorrow.

Comprehensive transcriptomic and metabolomic analysis revealed distinct flavonoid biosynthesis regulation during abnormal pistil development in Japanese apricot

Japanese apricot is an imperative stone fruit plant with numerous processing importance. The failure of reproductive system is the most common cause of fruit loss, through which pistil abortion is the fundamental one. To understand this mechanism, we used a combination of transcriptomic and metabolomic approaches to investigate the biochemical and molecular basis of flavonoid biosynthesis. Due to the regulated expression of flavonoid pathway-related genes in plants, flavonoid biosynthesis is largely regulated at the transcriptional level. A total of 2272 differently expressed genes and 215 differential metabolites were found. The expression of the genes and metabolites encoding flavonoid biosynthesis was lower in abnormal pistils that are in line with the flavonoid quantification from abnormal pistils. Besides, a couple of genes were also detected related to MYB, MADS, NAC and bHLH transcription factors. Remarkably, we found 'hydroxycinnamoyl transferase (LOC103323133)' and flavonoid related metabolite '2-hydroxycinnamic acid' was lower expressed in abnormal pistil, proposing the cause of pistil abortion. Collectively, the present study delivers inclusive transcriptional and metabolic datasets that proposed valuable prospects to unravel the genetic mechanism underlying pistil abortion.

Comparative Analysis of Tolerance to Salt Stress and Water Deficit in Two Invasive Weeds of the Genus Erigeron (Asteraceae)

Erigeron bonariensis and E. sumatrensis are two noxious weeds present in many parts of the world. Their tolerance to salinity and water deficit was analysed at the seed germination stage and during vegetative development. Seed germination was tested in solutions with different concentrations of NaCl and polyethylene glycol (PEG). Growth parameters, photosynthetic pigments, ion accumulation, and antioxidant mechanisms were analysed in plants that were subjected to increasing NaCl solutions, or severe water deficit by completely restricting irrigation. Seed germination was mostly affected by NaCl, but less by PEG in both species. E. bonariensis had a faster germination in all treatments and maintained a higher percentage of germination under the highest concentration of salt applied. Growth responses were similar in the two species, both being more affected by higher salt concentrations than by water deficit. The main differences in the responses of the two species to stress regard K⁺ and proline concentration. K⁺ in roots decreased under salt stress in E. sumatrensis, but remained constant in leaves, whereas in E. bonariensis increased in roots and leaves in salt-stressed plants. Proline concentration increased in all E. bonariensis plants under salt stress, but only in those under the highest salt concentration in E. sumatrensis. The results obtained indicate that the two species are relatively tolerant to water deficit and medium salinity but are susceptible to high NaCl concentrations.

Comparative Transcriptomic Analysis of Root and Leaf Transcript Profiles Reveals the Coordinated Mechanisms in Response to Salinity Stress in Common Vetch

Owing to its strong environmental suitability to adverse abiotic stress conditions, common vetch (Vicia sativa) is grown worldwide for both forage and green manure purposes and is an important protein source for human consumption and livestock feed. The germination of common vetch seeds and growth of seedlings are severely affected by salinity stress, and the response of common vetch to salinity stress at the molecular level is still poorly understood. In this study, we report the first comparative transcriptomic analysis of the leaves and roots of common vetch under salinity stress. A total of 6361 differentially expressed genes were identified in leaves and roots. In the roots, the stress response was dominated by genes involved in peroxidase activity. However, the genes in leaves focused mainly on Ca²⁺ transport. Overexpression of six salinity-inducible transcription factors in yeast further confirmed their biological functions in the salinity stress response. Our study provides the most comprehensive transcriptomic analysis of common vetch leaf and root responses to salinity stress. Our findings broaden the knowledge of the common and distinct intrinsic molecular mechanisms within the leaves and roots of common vetch and could help to develop common vetch cultivars with high salinity tolerance.