Apigenin pretreatment enhances growth and salinity tolerance of rice seedlings

Morphological, physiological, and transcriptomic analyses indicate that cell wall properties and antioxidant processes are potential targets for improving the aluminium tolerance of broad beans

Aluminium (Al) stress is the second-leading abiotic stress on crops. An improved understanding of the response mechanisms of plants to Al stress will provide scientific guidance for enhancing the crops' tolerance to Al stress. In this study, Al stress (50-200 μM AlCl3) caused visible damage to broad bean (Vicia faba L.) roots rather than shoots, which was attributed to Al accumulation and distribution in different tissues. Root transcriptomic analysis revealed that Al stress altered cell wall properties by downregulating lignin synthesis and several xyloglucan endotransglucosylase/hydrolase-, expansin- and peroxidase (POD)-encoding genes, which likely weakened cell extensibility to inhibit root growth. Additionally, Al stress impeded reactive oxygen species scavenging pathways involving POD activity and flavonoid biosynthesis, leading to oxidative damage characterised by malondialdehyde accumulation. These results indicate that optimising cell wall properties and/or enhancing antioxidant processes are crucial for alleviating Al toxicity to broad beans. Interestingly, exogenous application (500 and 1000 μM) of the flavonoid apigenin effectively alleviated Al toxicity in broad bean roots by partially improving the total antioxidant capacity of the roots. This study contributes to understanding the interaction between plants and Al and provides new strategies to alleviate Al toxicity in crops.

SOS! Hydrogen Sulfide Enhances the Flavonoid Early Warning System in Rice Plants to Cope with Thiocyanate Pollution

The presence of thiocyanate (SCN-) in irrigation water has adverse effects on both plant growth and crop output. Hydrogen sulfide (H2S) is an important gaseous signaling molecule that can alleviate SCN- stress. Flavonoids are secondary compounds produced by plants and are ubiquitous in the plant kingdom. They play important roles in several physiological and biochemical processes. To investigate the effect of exogenous H2S on the growth of early rice plants under SCN- stress, we carried out a hydroponic experiment focusing on the interaction of exogenous H2S with flavonoids. In this study, a hydroponic experiment was performed to investigate the behavior of SCN- when subjected to varying effective doses (EC20: 24.0 mg/L; EC50: 96.0 mg/L; and EC75: 300.0 mg/L). The findings indicated that the relative growth rate (RGR) of the plants treated with H2S + SCN- was greater than that of the plants treated with SCN- alone. Higher amounts of flavonoids were detected in the shoots than in the roots, with more variability in the shoots. The early warning level results showed that most of the flavonoids were present at levels I and II, while quercetin was present at level IV. Genetic expression variation factor (GEVF) analyses revealed an increase in the quantity of "promoter genes" with increasing SCN- concentration in both rice tissues. Furthermore, administering external H2S while exposing rice tissues to SCN- resulted in a considerable decrease in the levels of reactive oxygen species. This study provides novel insights into the regulation of flavonoid levels in rice plants by exogenous H2S, facilitating enhanced resistance to SCN- stress and promoting sustainable agriculture.

Ultrastructure and development of the floral nectary from Borago officinalis L. and phytochemical changes in its secretion

Although Boraginaceae have been classified as good sources of nectar for many insects, little is still known about their nectar and nectaries. Thus, in the present contribution, we investigated the nectar production dynamics and chemistry in Borago officinalis L. (borage or starflower), together with its potential interaction capacity with pollinators. A peak of nectar secretion (∼5.1 µL per flower) was recorded at anthesis, to decrease linearly during the following 9 days. In addition, TEM and SEM analyses were performed to understand ultrastructure and morphological changes occurring in borage nectary before and after anthesis, but also after its secretory phase. Evidence suggested that nectar was transported by the apoplastic route (mainly from parenchyma to epidermis) and then released essentially by exocytotic processes, that is a granulocrine secretion. This theory was corroborated by monitoring the signal of complex polysaccharides and calcium, respectively, via Thiéry staining and ESI/EELS technique. After the secretory phase, nectary underwent degeneration, probably through autophagic events and/or senescence induction. Furthermore, nectar (Nec) and other flower structures (i.e., sepals, gynoecia with nectaries, and petals) from borage were characterized by spectrophotometry and HPLC-DAD, in terms of plant secondary metabolites, both at early (E-) and late (L-) phase from anthesis. The content of phytochemicals was quantified and discussed for all samples, highlighting potential biological roles of these compounds in the borage flower (e.g., antimicrobial, antioxidant, staining effects). Surprisingly, a high significant accumulation of flavonoids was registered in L-Nec, with respect to E-Nec, indicating that this phenomenon might be functional and able to hide molecular (e.g., defence against pathogens) and/or ecological (e.g., last call for pollinators) purposes. Indeed, it is known that these plant metabolites influence nectar palatability, encouraging the approach of specialist pollinators, deterring nectar robbers, and altering the behaviour of insects.

Effects and mechanisms of proanthocyanidins-derived carbon dots on alleviating salt stress in rice by muti-omics analysis

Carbon dots (CDs) with different structures were prepared by electrolysis (PE-CDs) and hydrothermal (PH-CDs) methods using proanthocyanidins as precursors. The smaller size and lower zeta potential enabled the PE-CDs treated rice seedlings to exhibit greater resistance to salt stress. The fresh weight of rice seedlings under salt stress was significantly increased by spraying CDs every other day for two weeks. PE-CDs treated group exhibited a faster electron transport rate, and the SOD activity and flavonoid content were 2.5-fold and 0.23-fold higher than those of the salt stress-treated group. Furthermore, the metabolomics and transcriptomics analysis revealed that the PsaC gene of photosystem I was significantly up-regulated under PE-CDs treatment, which accelerated electron transfer in photosystem I. The up-regulation of BX1 and IGL genes encoding indole synthesis allowed rice to enhance stress tolerance through tryptophan and benzoxazine biosynthesis pathways. These findings offer help in purposefully synthesizing CDs and boosting food production.

Metabolite-based genome-wide association studies enable the dissection of the genetic bases of flavonoids, betaine and spermidine in wolfberry (Lycium)

Wolfberry is a plant with medicinal and food values. However, its bioactive ingredients and the corresponding genetic bases have not been determined. Here, we de novo generated a chromosome-level genome assembly for wolfberry, yielding a genome sequence of ~1.77 Gb with contig N50 of 50.55 Mb and 39 224 predicted gene models. A variation map, using 307 re-sequenced accessions, was called based on this genome assembly. Furthermore, the fruit metabolome of these accessions was profiled using 563 annotated metabolites, which separated Lycium barbarum L. and non-L. barbarum L. The flavonoids, coumarins, alkaloids and nicotinic acid contents were higher in the former than in the latter. A metabolite-based genome-wide association study mapped 156 164 significant single nucleotide polymorphisms corresponding to 340 metabolites. This included 19 219 unique lead single nucleotide polymorphisms in 1517 significant association loci, of which three metabolites, flavonoids, betaine and spermidine, were highlighted. Two candidate genes, LbUGT (evm.TU.chr07.2692) and LbCHS (evm.TU.chr07.2738), with non-synonymous mutations, were associated with the flavonoids content. LbCHS is a structural gene that interacts with a nearby MYB transcription factor (evm.TU.chr07.2726) both in L. barbarum and L. ruthenicum. Thus, these three genes might be involved in the biosynthesis/metabolism of flavonoids. LbSSADH (evm.TU.chr09.627) was identified as possibly participating in betaine biosynthesis/metabolism. Four lycibarbarspermidines (E-G and O) were identified, and only the lycibarbarspermidines O content was higher in L. barbarum varieties than in non-L. barbarum varieties. The evm.TU.chr07.2680 gene associated with lycibarbarspermidines O was annotated as an acetyl-CoA-benzylalcohol acetyltransferase, suggesting that it is a candidate gene for spermidine biosynthesis. These results provide novel insights into the specific metabolite profile of non-L. barbarum L. and the genetic bases of flavonoids, betaine and spermidine biosynthesis/metabolism.

Transcriptome and metabolome analyses reveal the regulatory role of MdPYL9 in drought resistance in apple

BACKGROUND

The mechanisms by which the apple MdPYL9 gene mediates the response to drought stress remain unclear. Here, transcriptome and metabolome analyses of apple plants under drought were used to investigate the mechanisms by which MdPYL9 regulates the response to drought stress in apple. MdPYL9-overexpressed transgenic and non-transgenic apple histoculture seedlings were rooted, transplanted, and subjected to drought treatments to clarify the mechanisms underlying the responses of apples to drought stress through phenotypic observations, physiological and biochemical index measurements, and transcriptomic and metabolomic analyses.

RESULTS

Under drought stress treatment, transgenic plants were less affected by drought stress than non-transgenic plants. Decreases in the net photosynthetic rate, stomatal conductance, and transpiration rate of transgenic apple plants were less pronounced in transgenic plants than in non-transgenic plants, and increases in the intercellular CO2 concentration were less pronounced in transgenic plants than in non-transgenic plants. The relative electrical conductivity and content of malondialdehyde, superoxide anion, and hydrogen peroxide were significantly lower in transgenic plants than in non-transgenic plants, and the chlorophyll content and activities of antioxidant enzymes (superoxide dismutase, peroxidase, and catalase) were significantly higher in transgenic plants than in non-transgenic plants. The number of differentially expressed genes (DEGs) involved in the response to drought stress was lower in transgenic plants than in non-transgenic plants, and the most significant and highly annotated DEGs in the transgenic plants were involved in the flavonoid biosynthesis pathway, and the most significant and highly annotated DEGs in control plants were involved in the phytohormone signal transduction pathway. The number of differentially accumulated metabolites involved in the response to drought stress was lower in transgenic plants than in non-transgenic plants, and up-regulated metabolites were significantly enriched in apigenin-7-O-glucoside in transgenic plants and in abscisic acid in non-transgenic plants. In the flavonoid biosynthetic pathway, the expression of genes encoding chalcone synthase (CHS) and chalcone isomerase (CHI) was more significantly down-regulated in non-transgenic plants than in transgenic plants, and the expression of the gene encoding 4-coumarate-CoA ligase (4CL) was more significantly up-regulated in transgenic plants than in non-transgenic plants, which resulted in the significant up-regulation of apigenin-7-O-glucoside in transgenic plants.

CONCLUSIONS

The above results indicated that the over-expression of MdPYL9 increased the drought resistance of plants under drought stress by attenuating the down-regulation of the expression of genes encoding CHS and CHI and enhancing the up-regulated expression of the gene encoding 4CL, which enhanced the content of apigenin-7-O-glucoside.

Potassium transporter OsHAK17 may contribute to saline-alkaline tolerant mechanisms in rice (Oryza sativa)

Rice production is seriously affected by saline-alkaline stress worldwide. To elucidate the saline-alkaline tolerance mechanisms in a novel tolerant rice variety, Shwe Nang Gyi (SNG), we investigated ion accumulation in SNG and Koshihikari (KSH), which is a saline-alkaline sensitive rice variety, and the candidates for saline-alkaline inducible genes in SNG using RNA-seq. SNG had superior ion accumulation capacity, such as K and Zn, compared to KSH. In contrast, SNG accumulated the same level of Na content in its leaf blades as KSH despite the higher dry weight of the SNG leaf blades. We further found that the expression of numerous genes, including several K+ transporter/high-affinity K+ transporter/K+ uptake protein/K+ transporter (HAK/KUP/KT) family members, were upregulated in SNG, and that OsHAK17 and OsHAK21 expression levels in the roots were significantly higher in SNG than in KSH. Moreover, yeast complementation analysis revealed that OsHAK17 was involved in K+ uptake under high-Na conditions. These results suggested that SNG has an effective K+ acquisition system supported by OsHAK17 functioning in saline-alkaline environments.

Integrated Metabolomics and Transcriptomics Analyses Highlight the Flavonoid Compounds Response to Alkaline Salt Stress in Glycyrrhiza uralensis Leaves

Glycyrrhiza uralensis is a saline-alkali-tolerant plant whose aerial parts are rich in flavonoids; however, the role of these flavonoids in saline-alkali tolerance remains unclear. Herein, we performed physiological, metabolomics, and transcriptomics analyses in G. uralensis leaves under alkaline salt stress for different durations. Alkaline salt stress stimulated excessive accumulation of reactive oxygen species and consequently destroyed the cell membrane, causing cell death, and G. uralensis initiated osmotic regulation and the antioxidant system to respond to stress. In total, 803 metabolites, including 244 flavonoids, were detected via metabolomics analysis. Differentially altered metabolites and differentially expressed genes were coenriched in flavonoid-related pathways. Genes such as novel.4890, Glyur001511s00039602, and Glyur000775s00025737 were highly expressed, and flavonoid metabolites such as 2'-hydroxygenistein, apigenin, and 3-O-methylquercetin were upregulated. Thus, flavonoids as nonenzymatic antioxidants play an important role in stress tolerance. These findings provide novel insights into the response of G. uralensis to alkaline salt stress.

Integrated transcriptomic and metabolomic analyses elucidate the mechanism of flavonoid biosynthesis in the regulation of mulberry seed germination under salt stress

Seed propagation is the main method of mulberry expansion in China, an important economic forest species. However, seed germination is the most sensitive stage to various abiotic stresses, especially salinity stress. To reveal the molecular regulatory mechanism of mulberry seed germination under salt stress, flavonoid metabolomics and transcriptomics analyses were performed on mulberry seeds germinated under 50 and 100 mmol/L NaCl stress. Analysis of the flavonoid metabolome revealed that a total of 145 differential flavonoid metabolites (DFMs) were classified into 9 groups, 40 flavonols, 32 flavones, 16 chalcones and 14 flavanones. Among them, 61.4% (89) of the DFMs accumulated continuously with increasing salt concentration, reaching the highest level at a 100 mmol/L salt concentration; these DFMs included quercetin-3-O-glucoside (isoquercitrin), kaempferol (3,5,7,4'-tetrahydroxyflavone), quercetin-7-O-glucoside, taxifolin (dihydroquercetin) and apigenin (4',5,7-trihydroxyflavone), indicating that these flavonoids may be key metabolites involved in the response to salt stress. Transcriptional analysis identified a total of 3055 differentially expressed genes (DEGs), most of which were enriched in flavonoid biosynthesis (ko00941), phenylpropanoid biosynthesis (ko00940) and biosynthesis of secondary metabolites (ko01110). Combined analysis of flavonoid metabolomic and transcriptomic data indicated that phenylalanine ammonia-lyase (PAL), 4-coumarate-CoA ligase (4CL), chalcone synthase (CHS), flavonol synthase (FLS), bifunctional dihydroflavonol 4-reductase/flavanone 4-reductase (DFR) and anthocyanidin reductase (ANR) were the key genes involved in flavonoid accumulation during mulberry seed germination under 50 and 100 mmol/L NaCl stress. In addition, three transcription factors, MYB, bHLH and NAC, were involved in the regulation of flavonoid accumulation under salt stress. The results of quantitative real-time PCR (qRT‒PCR) validation showed that the expression levels of 11 DEGs, including 7 genes involved in flavonoid biosynthesis, under different salt concentrations were consistent with the transcriptomic data, and parallel reaction monitoring (PRM) results showed that the expression levels of 6 key enzymes (proteins) involved in flavonoid synthesis were consistent with the accumulation of flavonoids. This study provides a new perspective for investigating the regulatory role of flavonoid biosynthesis in the regulation of mulberry seed germination under salt stress at different concentrations.

Exogenous riboflavin (vitamin B2) application enhances salinity tolerance through the activation of its biosynthesis in rice seedlings under salinity stress

Salinity stress triggers the accumulation of reactive oxygen species (ROS), leading to impaired plant growth. Riboflavin (RIB; vitamin B2) is synthesized by plants, fungi, and microorganisms and is a precursor of the coenzymes, flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), which are important for cellular metabolism. In this study, we aimed to elucidate the mechanistic basis of the RIB-mediated alleviation of salinity stress in rice. We observed higher biomass accumulation and lower concentrations of malondialdehyde (MDA) and hydrogen peroxide (H2O2) in RIB-pretreated seedlings under salinity stress. In vitro assays showed that H2O2 was scavenged as the RIB concentration increased, implying that RIB may function as a non-enzymatic antioxidant in ROS detoxification. RIB-pretreated seedlings accumulated more Na+ in the roots than in the leaf blades because of the contributions of OsHKT2;1, OsNHX1, and OsHKT1;4 in the roots and leaf sheaths, respectively. Liquid chromatography-mass spectrometry (LC-MS/MS) analysis revealed increased RIB concentration in roots and shoots and upregulation of key genes (OsRIBA1, OsGCHI, OsLS, and OsRS) involved in RIB biosynthesis in the roots of RIB-pretreated seedlings. Taken together, our findings suggest that RIB pretreatment ameliorates salinity stress in rice by improving (1) oxidative stress tolerance, as increased RIB concentration may function as a non-enzymatic antioxidant, and (2) ionic stress tolerance, as RIB pretreatment limits Na+ accumulation in the leaf blades and maintains a favorable Na+/K+ balance.

Comparative analysis of defensive secondary metabolites in wild teosinte and cultivated maize under flooding and herbivory stress

Climate change is driving an alarming increase in the frequency and intensity of abiotic and biotic stress factors, negatively impacting plant development and agricultural productivity. To survive, plants respond by inducing changes in below and aboveground metabolism with concomitant alterations in defensive secondary metabolites. While plant responses to the isolated stresses of flooding and insect herbivory have been extensively studied, much less is known about their response in combination. Wild relatives of cultivated plants with robust stress tolerance traits provide an excellent system for comparing how diverse plant species respond to combinatorial stress, and provide insight into potential germplasms for stress-tolerant hybrids. In this study, we compared the below and aboveground changes in the secondary metabolites of maize (Zea mays) and a flood-tolerant wild relative Nicaraguan teosinte (Zea nicaraguensis) in response to flooding, insect herbivory, and their combination. Root tissue was analyzed for changes in belowground metabolism. Leaf total phenolic content and headspace volatile organic compound emission were analyzed for changes in aboveground secondary metabolism. Results revealed significant differences in the root metabolome profiles of teosinte and maize. Notably, the accumulation of the flavonoids apigenin, naringenin, and luteolin during flooding and herbivory differentiated teosinte from maize. Aboveground, terpenes, including trans-α-bergamotene and (E)-4,8-dimethylnona-1,3,7-triene, shaped compositional differences in their volatile profiles between flooding, herbivory, and their combination. Taken together, these results suggest teosinte may be more tolerant than maize due to dynamic metabolic changes during flooding and herbivory that help relieve stress and influence plant-insect interactions.

Quercetin-mediated alteration in photosynthetic efficiency, sugar metabolism, elemental status, yield, and redox potential in two varieties of okra

Quercetin is a bioactive natural compound with an antioxidative property that can potentially modify plant physiology. The current investigation aimed to gauge the effect of different concentrations of foliar spray of quercetin (0, 0.5, 1, 1.5, 2.0 mM) on several morphological and physio-biochemical performances of Abelmoschus esculentus L. (Moench.) plants under normal environmental conditions. The foliar spray on the plant leaves was applied 25 days after sowing (DAS) and continued up to 30 DAS once each day. The plants were sampled at 30 and 45 DAS to monitor several parameters. The foliar treatments of quercetin significantly upgraded all the studied parameters. The results direct that most of the traits such as growth, nutrient uptake, photosynthetic, and enzyme activities were promoted in a dose-dependent way. Quercetin application lowered the reactive oxygen species (ROS) buildup by increasing the antioxidant enzyme activities. Microscopic investigations further revealed a significant enhancement in the stomatal aperture under quercetin application. Out of several doses tested, 1 mM of quercetin proved best and can be used for further investigations.

Comparative transcriptome analysis reveals the key genes and pathways involved in drought stress response of two wheat (Triticum aestivum L) varieties

Drought stress results in significant yield losses in wheat production. Although studies have reported a number of wheat drought tolerance genes, a deeper understanding of the tolerance mechanisms is required for improving wheat tolerance against drought stress. In this study, we found that "Deguo 2" exhibited higher tolerance to drought than "Truman". Transcriptomics analysis enabled identification of 6084 and 7146 differentially expressed genes (DEGs), mainly mapping flavonoid biosynthesis, plant hormone, phenolamides and antioxidant pathways and revealed altered expression levels of about 700 genes. Exogenous melatonin application enhanced wheat tolerance against drought stress. Co-expression analysis showed that bHLH and bZIP transcription factors may be involved in the regulation of various pathway genes. Take together, these results provide new insights for us on exploring the crosstalk between phytohormones and secondary metabolites, and will deepen the understanding of the complex tolerance mechanisms against drought stress in wheat.

Protective role of quercetin and kaempferol against oxidative damage and photosynthesis inhibition in wheat chloroplasts under arsenic stress

Arsenic (As) toxicity negatively impacts plant development, limits agricultural production, and, by entering the food chain, endangers human health. Studies on the use of natural and bioactive molecules in increasing plants' resistance to abiotic stressors, such as As, have gained increasing attention in the last few years. Flavonols are plant secondary metabolites with high potential in stress tolerance due to their roles in signal transmission. Therefore, the focus of this study was to examine the effects of two flavonols, quercetin (Q, 25 μM) and kaempferol (K, 25 μM), on growth parameters, photosynthesis, and chloroplastic antioxidant activity in wheat leaves under As stress (100 μM). As stress reduced the relative growth rate by 50% and relative water content by 25% in leaves. However, applying Q and/or K alleviated the As-induced suppression of growth and water relations. Exogenous phenolic treatments reversed the effects of As toxicity in photochemistry and maintained the photochemical quantum efficiency of the Photosystem II (Fv /Fm ). As exposure increased, the H2 O2 content in wheat chloroplasts by 42% and high levels of H2 O2 accumulation were also observed in guard cells in confocal microscopy images. Analysis of the chloroplastic antioxidant system has shown that Q and K applications increase the activity of antioxidant enzymes, including superoxide dismutase, peroxidase, and ascorbate peroxidase. Phenolic applications have induced the ascorbate-glutathione (AsA-GSH) cycle in charge of the protection of the cellular redox balance in different ways. It has been determined that Q triggers the AsA renewal, and K maintains the GSH pool. As a result, Q and K applications provide tolerance to wheat plants under As stress by increasing the chloroplastic antioxidant system activity and protecting photosynthetic reactions from oxidative damage. This study reveals the potential use of plant phenolic compounds in agricultural systems as a biosafe strategy to enhance plant stress tolerance, hence increasing yield.

Transcriptomic and metabolomic perspectives for the growth of alfalfa (Medicago sativa L.) seedlings with the effect of vanadium exposure

Hitherto, the effect of vanadium on higher plant growth remains an open topic. Therefore, nontargeted metabolomic and RNA-Seq profiling were implemented to unravel the possible alteration in alfalfa seedlings subjected to 0.1 mg L^-1 (B group) and 0.5 mg L^-1 (C group) pentavalent vanadium [(V(V)] versus control (A group) in this study. Results revealed that vanadium exposure significantly altered some pivotal transcripts and metabolites. The number of differentially expressed genes (DEGs) markedly up- and down-regulated was 21 and 23 in B_vs_A, 27 and 33 in C_vs_A, and 24 and 43 in C_vs_B, respectively. The number for significantly up- and down-regulated differential metabolites was 17 and 15 in B_vs_A, 43 and 20 in C_vs_A, and 24 and 16 in C_vs_B, respectively. Metabolomics and transcriptomics co-analysis characterized three significantly enriched metabolic pathways in C_vs_A comparing group, viz., α-linolenic acid metabolism, flavonoid biosynthesis, and phenylpropanoid biosynthesis, from which some differentially expressed genes and differential metabolites participated. The metabolite of traumatic acid in α-linolenic acid metabolism and apigenin in flavonoid biosynthesis were markedly upregulated, while phenylalanine in phenylpropanoid biosynthesis was remarkably downregulated. The genes of allene oxide cyclase (AOC) and acetyl-CoA acyltransferase (fadA) in α-linolenic acid metabolism, and chalcone synthase (CHS), flavonoid 3'-monooxygenase (CYP75B1), and flavonol synthase (FLS) in flavonoid biosynthesis, and caffeoyl-CoA O-methyltransferase (CCoAOMT) in phenylpropanoid biosynthesis were significantly downregulated. While shikimate O-hydroxycinnamoyltransferase (HCT) in flavanoid and phenylpropanoid biosynthesis were conspicuously upregulated. Briefly, vanadium exposure induces a readjustment yielding in metabolite and the correlative synthetic precursors (transcripts/unigenes) in some branched metabolic pathways. This study provides a practical and in-depth perspective from transcriptomics and metabolomics in investigating the effects conferred by vanadium on plant growth and development.

Estimation of rice seedling growth traits with an end-to-end multi-objective deep learning framework

In recent years, rice seedling raising factories have gradually been promoted in China. The seedlings bred in the factory need to be selected manually and then transplanted to the field. Growth-related traits such as height and biomass are important indicators for quantifying the growth of rice seedlings. Nowadays, the development of image-based plant phenotyping has received increasing attention, however, there is still room for improvement in plant phenotyping methods to meet the demand for rapid, robust and low-cost extraction of phenotypic measurements from images in environmentally-controlled plant factories. In this study, a method based on convolutional neural networks (CNNs) and digital images was applied to estimate the growth of rice seedlings in a controlled environment. Specifically, an end-to-end framework consisting of hybrid CNNs took color images, scaling factor and image acquisition distance as input and directly predicted the shoot height (SH) and shoot fresh weight (SFW) after image segmentation. The results on the rice seedlings dataset collected by different optical sensors demonstrated that the proposed model outperformed compared random forest (RF) and regression CNN models (RCNN). The model achieved R² values of 0.980 and 0.717, and normalized root mean square error (NRMSE) values of 2.64% and 17.23%, respectively. The hybrid CNNs method can learn the relationship between digital images and seedling growth traits, promising to provide a convenient and flexible estimation tool for the non-destructive monitoring of seedling growth in controlled environments.

Multifeature analysis of age-related microbiome structures reveals defense mechanisms of Populus tomentosa trees

Root microbiota composition shifts during the development of most annual plants. Although some perennial plants can live for centuries, the host-microbiome partnerships and interaction mechanisms underlying their longevity remain unclear. To address this gap, we investigated age-related changes in the root metabolites, transcriptomes, and microbiome compositions of 1- to 35-yr-old Populus tomentosa trees. Ten co-response clusters were obtained according to their accumulation patterns, and members of each cluster displayed a uniform and clear pattern of abundance. Multi-omics network analysis demonstrated that the increased abundance of Actinobacteria with tree age was strongly associated with the flavonoid biosynthesis. Using genetic approaches, we demonstrate that the flavonoid biosynthesis regulator gene Transparent Testa 8 is associated with the recruitment of flavonoid-associated Actinobacteria. Further inoculation experiments of Actinobacteria isolates indicated that their colonization could significantly improve the host's phenotype. Site-directed mutagenesis revealed that the hyBl gene cluster, involved in biosynthesis of an aminocyclitol hygromycin B analog in Streptomyces isolate bj1, is associated with disease suppression. We hypothesize that interactions between perennial plants and soil microorganisms lead to gradual enrichment of a subset of microorganisms that may harbor a wealth of currently unknown functional traits.

Integrative transcriptome and metabolome analysis reveals the mechanism of exogenous melatonin alleviating drought stress in maize roots

Melatonin (MT) is essential for plant development and drought adaptation. However, the molecular and metabolic mechanisms underlying MT-induced drought tolerance in maize roots remain largely unclear. Herein, we investigated the effects of MT on drought tolerance in maize roots using integrated transcriptomic and metabolomic analyses, and identified MT-induced genes and metabolites associated with drought resistance. Compared with the untreated control plants, MT application alleviated the deleterious effects of drought on roots, by decreasing the malondialdehyde level and increasing the solute potential, eventually promoting root growth. Transcriptome and metabolome analysis demonstrated that MT significantly upregulates the expression of genes related to flavonoid biosynthesis (PAL, C4H, 4CL, HCT, CHS, CHI, F3'5'H, and DFR), activates drought-responsive transcription factors (ERFs, NACs, MYBs, and bHLHs), and regulates hormone signaling-related genes, especially ethylene response factors (ERF4, ERF81, and ERF110). Moreover, MT increased the accumulation of flavonoid metabolites, particularly apigenin, luteolin, and quercetin, under drought-stress conditions. These findings were further supported by quantitative real-time polymerase chain reaction analysis and total flavonoid measurements. Altogether, our findings suggest that MT promotes maize root growth during drought by regulating flavonoid synthesis pathways, transcription factors, and plant hormone signals. This study provides new insights into the complex mechanisms by which MT enhances crop resistance to drought damage.

Visualizing the distribution of flavonoids in litchi (Litchi chinenis) seeds through matrix-assisted laser desorption/ionization mass spectrometry imaging

Flavonoids are one of the most important bioactive components in litchi (Litchi chinensis Sonn.) seeds and have broad-spectrum antiviral and antitumor activities. Litchi seeds have been shown to inhibit the proliferation of cancer cells and induce apoptosis, particularly effective against breast and liver cancers. Elucidating the distribution of flavonoids is important for understanding their physiological and biochemical functions and facilitating their efficient extraction and utilization. However, the spatial distribution patterns and expression states of flavonoids in litchi seeds remain unclear. Herein, matrix-assisted laser desorption/ionization mass spectrometry imaging (MALDI-MSI) was used for in situ detection and imaging of the distribution of flavonoids in litchi seed tissue sections for the first time. Fifteen flavonoid ion signals, including liquiritigenin, apigenin, naringenin, luteolin, dihydrokaempferol, daidzein, quercetin, taxifolin, kaempferol, isorhamnetin, myricetin, catechin, quercetin 3-β-d-glucoside, baicalin, and rutin, were successfully detected and imaged in situ through MALDI-MSI in the positive ion mode using 2-mercaptobenzothiazole as a matrix. The results clearly showed the heterogeneous distribution of flavonoids, indicating the potential of litchi seeds for flavonoid compound extraction. MALDI-MS-based multi-imaging enhanced the visualization of spatial distribution and expression states of flavonoids. Thus, apart from improving our understanding of the spatial distribution of flavonoids in litchi seeds, our findings also facilitate the development of MALDI-MSI-based metabolomics as a novel effective molecular imaging tool for evaluating the spatial distribution of endogenous compounds.

Identification and Analysis of Metabolites That Contribute to the Formation of Distinctive Flavour Components of Laoxianghuang

In addition to volatile compounds, metabolites also have a great effect on the flavour of food. Fresh finger citron cannot be eaten directly because of its spicy and bitter taste, so it is made into a preserved fruit product known as Laoxianghuang (LXH). To investigate the metabolites that have an effect on the flavour of LXH, untargeted metabolomics was performed using an ultrahigh-performance liquid chromatography with tandem mass spectrometry (UPLC-MS/MS), and the metabolites of the Laoxianghuang samples from different locations in the Chaoshan area were compared and analysed. A total of 756 metabolites were identified and distinct differences were revealed among the different Laoxianghuang samples. A total of 33 differential metabolites with the most significant changes were screened through further multivariate analytical steps, and each group of samples had unique metabolites. For instance, pomolic acid had the highest content in the JG sample, while L-glycyl-L-isoleucine was rich in the QS sample. Moreover, flavonoid metabolites made the greatest contribution to the unique flavour of Laoxianghuang. The metabolic pathways involved are the biosynthetic pathways of flavonoids, isoflavonoids, flavones, and flavonols. This study can provide some creative information for distinguishing the quality differences of Laoxianghuang from the perspective of metabolites and offer preliminary theoretical support to characterise the formation of flavour substances in Laoxianghuang.

Supportive effect of naringenin on NaCl-induced toxicity in Carthamus tinctorius seedlings

In the present study, we used exogenous naringenin (0.5 mM) pretreatment before the stress (25 mM NaCl) on the growth and tolerance of safflower seedlings under non-salinity conditions and salinity conditions. Our results showed that salinity treatment significantly declined the biomass, leaf relative water content, chlorophyll content, K⁺ content, and K⁺/Na⁺ ratio by 28%, 28%, 12%, 36%, and 56%, respectively, as compared to untreated control. The results obtained in the present study showed the beneficial effects of the pretreatment of naringenin in safflower seedlings under non-salinity conditions concerning increasing plant biomass, total phenolic compound, radical scavenging activity (RSA), soluble sugar content, proline, glutathione, enzymatic antioxidants, and K⁺ content. Nevertheless, naringenin pretreated plants showed a clear increment in the values of biomass, RSA, total phenolic compound, and catalase enzyme activity parameters under salinity stress. Salinity stress caused ionic phytotoxicity and oxidative stress by enhancing Na⁺ content, H₂O₂ accumulation, malondialdehyde (MDA), and antioxidants. However, naringenin alleviated salt-induced oxidative stress by decreasing H₂O₂ and MDA content in the leaves and improving the catalase activity in treated plants. Generally, it could be concluded pretreatment of naringenin before stress could partly diminish NaCl-caused oxidative stress in safflower seedlings, probably due to improvement in enzymatic and non-enzymatic antioxidants and reduced cell membrane damage.

Triacontanol priming as a smart strategy to attenuate lead toxicity in Brassica oleracea L

The most prevalent heavy metal pollutant in the environment is lead (Pb). Lead potentially contribute 10% of overall heavy metal contamination. Lead uptake by plants has been found to have an impact on their metabolic functions, photosynthetic activity, growth, and productivity. The current experiment was conducted to investigate the impact of triacontanol (Tria) for attenuating Pb stress in Brassica oleracea var. italic (broccoli). Three different Tria concentrations (10, 20 and 30 µmol L^-1) were used to prime broccoli seeds. Growth of broccoli was reduced when exposed to Pb-driven toxicity. Additionally, Pb had a deleterious impact on the protein quantity, stomatal conductance, transpiration and photosynthetic rate. Nevertheless, plants grown from seeds primed with Tria2 (20 µmol L^-1 Tria) exhibited improved morphological characteristics, uptake of mineral content (Mn⁺², Zn⁺², K⁺¹, Na⁺¹) along with biomass production. There was 1.6-fold increase in photosynthetic rate, the phenol (1.3 folds), and DPPH activity (1.2 folds) in seed primed with Tria2. Additionally, plants treated with Tria2 demonstrated enhanced MTI and gas exchange characteristics that improves plant stress tolerance under Pb stress. Seed priming with Tria can be used to increase plant tolerance to Pb stress as evidenced by the improved growth and biochemical characteristics of broccoli seedlings.

Stb6 mediates stomatal immunity, photosynthetic functionality, and the antioxidant system during the Zymoseptoria tritici-wheat interaction

This study offers new perspectives on the biochemical and physiological changes that occur in wheat following a gene-for-gene interaction with the fungal pathogen Zymoseptoria tritici. The Z. tritici isolate IPO323, carries AvrStb6, while ΔAvrStb6#33, lacks AvrStb6. The wheat cultivar (cv.) Shafir, bears the corresponding resistance gene Stb6. Inoculation of cv. Shafir with these isolates results in two contrasted phenotypes, offering a unique opportunity to study the immune response caused by the recognition of AvrStb6 by Stb6. We employed a variety of methodologies to dissect the physiological and biochemical events altered in cv. Shafir, as a result of the AvrStb6-Stb6 interaction. Comparative analysis of stomatal conductance demonstrated that AvrStb6-Stb6 mediates transient stomatal closures to restrict the penetration of Zymoseptoria tritici. Tracking photosynthetic functionality through chlorophyll fluorescence imaging analysis demonstrated that AvrStb6-Stb6 retains the functionality of photosynthesis apparatus by promoting Non-Photochemical Quenching (NPQ). Furthermore, the PlantCV image analysis tool was used to compare the H₂O₂ accumulation and incidence of cell death (2, 4, 8, 12, 16, and 21 dpi), over Z. tritici infection. Finally, our research shows that the AvrStb6-Stb6 interaction coordinates the expression and activity of antioxidant enzymes, both enzymatic and non-enzymatic, to counteract oxidative stress. In conclusion, the Stb6-AvrStb6 interaction in the Z. tritici-wheat pathosystem triggers transient stomatal closure and maintains photosynthesis while regulating oxidative stress.

Seaweed-Derived Phenolic Compounds in Growth Promotion and Stress Alleviation in Plants

Abiotic and biotic stress factors negatively influence the growth, yield, and nutritional value of economically important food and feed crops. These climate-change-induced stress factors, together with the ever-growing human population, compromise sustainable food security for all consumers across the world. Agrochemicals are widely used to increase crop yield by improving plant growth and enhancing their tolerance to stress factors; however, there has been a shift towards natural compounds in recent years due to the detrimental effect associated with these agrochemicals on crops and the ecosystem. In view of these, the use of phenolic biostimulants as opposed to artificial fertilizers has gained significant momentum in crop production. Seaweeds are marine organisms and excellent sources of natural phenolic compounds that are useful for downstream agricultural applications such as promoting plant growth and improving resilience against various stress conditions. In this review, we highlight the different phenolic compounds present in seaweed, compare their extraction methods, and describe their downstream applications in agriculture.

Fungicide-loaded mesoporous silica nanoparticles promote rice seedling growth by regulating amino acid metabolic pathways

Mesoporous silica nanoparticles (MSN) are widely researched as carriers for pesticides (including fungicides, insecticides and herbicides) to improve their effective utilization rate in the target plant. However, pesticides enter the target crops and may bring some impacts on the growth and physiological function of plants. When they are loaded to nanoparticles, different effects on the metabolic properties of target plants will be produced. In this study, thifluzamide-loaded MSN was prepared with average diameter of 80-120 nm. Rice seedlings were exposed for 7 days to different treatments of MSN, thifluzamide, and thifluzamide-loaded MSN. After treatment, non-targeted metabolomic method was employed to explore the metabolic pathways. It was found that the negative effect of thifluzamide to rice seedling was alleviated by thifluzamide-loaded MSN, since it increased amino acid metabolic pathways, which improved purine and pyrimidine metabolism and induced the production of total protein. Thifluzamide-loaded MSN can also relieve the damage of thifluzamide to rice seedlings by altering the chlorophyll, phenols and flavonoids content. In conclusion, it was proposed that the mechanism of fungicide-loaded MSN prevent plant from negative effects of fungicides by regulating the amino acid metabolic pathways.

A novel transcription factor CmMYB012 inhibits flavone and anthocyanin biosynthesis in response to high temperatures in chrysanthemum

Flavones are among the major colorless pigments synthesized through branches of the flavonoid pathway in plants. However, due to the absence of a gene encoding flavone synthase (FNS) in the model plant Arabidopsis thaliana species, the regulatory mechanism of FNS-catalyzed flavone biosynthesis has rarely been studied in plants. Here, it was found that flavones play a predominant role in the elimination of excess reactive oxygen species (ROS) at high temperatures in colorless plant organs. A novel atypical subgroup 7 (SG7) R2R3-MYB transcription factor, CmMYB012, was found to be induced in response to prolonged high temperatures and to inhibit flavone biosynthesis by directly regulating CmFNS. Moreover, CmMYB012 was also found to inhibit anthocyanin biosynthesis by suppressing the expression of CmCHS, CmDFR, CmANS, and CmUFGT. CmMYB012 overexpression exerted a negative influence on plant fitness and pink flower color formation, while CmMYB012 suppression had the opposite effect in response to high temperatures. Our findings provide new insights into the mechanisms by which high temperatures regulate the metabolism of flavones and anthocyanins to affect plant fitness and flower color formation.

Metabolomics and Physiological Insights into the Ability of Exogenously Applied Chlorogenic Acid and Hesperidin to Modulate Salt Stress in Lettuce Distinctively

Recent studies in the agronomic field indicate that the exogenous application of polyphenols can provide tolerance against various stresses in plants. However, the molecular processes underlying stress mitigation remain unclear, and little is known about the impact of exogenously applied phenolics, especially in combination with salinity. In this work, the impacts of exogenously applied chlorogenic acid (CA), hesperidin (HES), and their combination (HES + CA) have been investigated in lettuce (Lactuca sativa L.) through untargeted metabolomics to evaluate mitigation effects against salinity. Growth parameters, physiological measurements, leaf relative water content, and osmotic potential as well as gas exchange parameters were also measured. As expected, salinity produced a significant decline in the physiological and biochemical parameters of lettuce. However, the treatments with exogenous phenolics, particularly HES and HES + CA, allowed lettuce to cope with salt stress condition. Interestingly, the treatments triggered a broad metabolic reprogramming that involved secondary metabolism and small molecules such as electron carriers, enzyme cofactors, and vitamins. Under salinity conditions, CA and HES + CA distinctively elicited secondary metabolism, nitrogen-containing compounds, osmoprotectants, and polyamines.

Regulation of Reactive Oxygen Species and Antioxidant Defense in Plants under Salinity

The generation of oxygen radicals and their derivatives, known as reactive oxygen species, (ROS) is a part of the signaling process in higher plants at lower concentrations, but at higher concentrations, those ROS cause oxidative stress. Salinity-induced osmotic stress and ionic stress trigger the overproduction of ROS and, ultimately, result in oxidative damage to cell organelles and membrane components, and at severe levels, they cause cell and plant death. The antioxidant defense system protects the plant from salt-induced oxidative damage by detoxifying the ROS and also by maintaining the balance of ROS generation under salt stress. Different plant hormones and genes are also associated with the signaling and antioxidant defense system to protect plants when they are exposed to salt stress. Salt-induced ROS overgeneration is one of the major reasons for hampering the morpho-physiological and biochemical activities of plants which can be largely restored through enhancing the antioxidant defense system that detoxifies ROS. In this review, we discuss the salt-induced generation of ROS, oxidative stress and antioxidant defense of plants under salinity.

The pigeon pea CcCIPK14-CcCBL1 pair positively modulates drought tolerance by enhancing flavonoid biosynthesis

Calcineurin B-like (CBL)-interacting protein kinases (CIPKs) play a central role in Ca²⁺ signalling and promote drought tolerance in plants. The CIPK gene family in pigeon pea (Cajanus cajan L.), a major food crop affected by drought, has not previously been characterised. Here, we identified 28 CIPK genes in the pigeon pea genome. Five CcCIPK genes were strongly upregulated in roots upon drought treatment and were selected for further characterisation. Overexpression of CcCIPK13 and CcCIPK14 increased survival rates by two- to three-fold relative to controls after 14 days of drought. Furthermore, the three major flavonoids, genistin, genistein and apigenin, were significantly upregulated in the same transgenic plants. Using CcCIPK14 as bait, we performed a yeast two-hybrid screen and identified six interactors, including CcCBL1. CcCIPK14 exhibited autophosphorylation and phosphorylation of CcCBL1 in vitro. CcCBL1-overexpressed plants displayed higher survival rates upon drought stress as well as higher expression of flavonoid biosynthetic genes and flavonoid content. CcCIPK14-overexpressed plants in which CcCBL1 transcript levels were reduced by RNA interference had lower survival rates, which indicated CcCBL1 in the same pathway as CcCIPK14. Together, our results demonstrate a role for the CcCIPK14-CcCBL1 complex in drought stress tolerance through the regulation of flavonoid biosynthesis in pigeon pea.

Coumarin improves tomato plant tolerance to salinity by enhancing antioxidant defence, glyoxalase system and ion homeostasis

Salinity is a severe threat to crop growth, development and even to world food sustainability. Plant possess natural antioxidant defense tactics to mitigate salinity-induced oxidative stress. Phenolic compounds are non-enzymatic antioxidants with specific roles in protecting plant cells against stress-mediated reactive oxygen species (ROS) generation. Coumarin (COU) is one of these compounds, however, to date, little is known about antioxidative roles of exogenous COU in enhancing plant tolerance mechanisms under salt stress. The involvement of COU in increasing tomato salt tolerance was examined in the present study using COU as a pre-treatment at 20 or 30 µM for 2 days against salt stress (100 or 160  NaCl; 5 days). The COU-mediated stimulation of plant antioxidant defence and glyoxalase systems to suppress salt-induced ROS and methylglyoxal (MG) toxicity, respectively, were the main hypotheses examined in the present study. Addition of COU suppressed salt-induced excess accumulation of ROS and MG, and significantly reduced membrane damage, lipid peroxidation and Na⁺ toxicity. These results demonstrate COU-improved plant growth, biomass content, photosynthetic pigment content, water retention and mineral homeostasis upon imposition of salinity. Finally, this present study suggests that COU has potential roles as a phytoprotectant in stimulating plant antioxidative mechanisms and improving glyoxalase enzyme activity under salinity stress.

Salinity Effects on Morpho-Physiological and Yield Traits of Soybean (Glycine max L.) as Mediated by Foliar Spray with Brassinolide

Salinity episodes that are common in arid regions, characterized by dryland, are adversely affecting crop production worldwide. This study evaluated the effectiveness of brassinolide (BL) in ameliorating salinity stress imposed on soybean at four levels (control (1.10), 32.40, 60.60 and 86.30 mM/L NaCl) in factorial combination with six BL application frequency (control (BL₀), application at seedling (BL₁), flowering (BL₂), podding (BL₃), seedling + flowering (BL₄) and seedling + flowering + podding (BL₅)) stages. Plant growth attributes, seed yield, and N, P, K, Ca and Mg partitioning to leaves, stems and roots, as well as protein and seed-N concentrations, were significantly (p ≤ 0.05) reduced by salinity stress. These trends were ascribed to considerable impairments in the photosynthetic pigments, photosynthetically active radiation, leaf stomatal conductance and relative water content in the leaves of seedlings under stress. The activity of peroxidase and superoxidase significantly (p ≤ 0.05) increased with salinity. Foliar spray with BL significantly (p ≤ 0.05) improved the photosynthetic attributes, as well as nutrient partitioning, under stress, and alleviated ion toxicity by maintaining a favourable K⁺/Na⁺ ratio and decreasing oxidative damage. Foliar spray with brassinolide could sustain soybean growth and seed yield at salt concentrations up to 60.60 mM/L NaCl.

The Role of Polyphenols in Abiotic Stress Response: The Influence of Molecular Structure

Abiotic stressors such as extreme temperatures, drought, flood, light, salt, and heavy metals alter biological diversity and crop production worldwide. Therefore, it is important to know the mechanisms by which plants cope with stress conditions. Polyphenols, which are the largest group of plant-specialized metabolites, are generally recognized as molecules involved in stress protection in plants. This diverse group of metabolites contains various structures, from simple forms consisting of one aromatic ring to more complex ones consisting of large number of polymerized molecules. Consequently, all these molecules, depending on their structure, may show different roles in plant growth, development, and stress protection. In the present review, we aimed to summarize data on how different polyphenol structures influence their biological activity and their roles in abiotic stress responses. We focused our review on phenolic acids, flavonoids, stilbenoids, and lignans.

Liquiritoside Alleviated Pb Induced Stress in Brassica rapa subsp. Parachinensis: Modulations in Glucosinolate Content and Some Physiochemical Attributes

Current research was conducted to explore the effects of liquiritoside on the growth and physiochemical features of Chinese flowering cabbage (Brassica rapa subsp. parachinensis) under lead (Pb) stress. Lead stressed B. rapa plants exhibited decreased growth parameters, chlorophyll, and carotenoid contents. Moreover, Pb toxicity escalated the synthesis of malondialdehyde (MDA), hydrogen peroxide (H₂O₂), flavonoids, phenolics, and proline in treated plants. Nevertheless, foliar application of liquiritoside mitigated Pb toxicity by decreasing oxidative stress by reducing cysteine, H₂O_2, and MDA contents in applied plants. Liquiritoside significantly increased plant height, shoot fresh weight and dry weight, number of leaves, and marketable value of Chinese flowering cabbage plants exposed to Pb toxicity. This biotic elicitor also enhanced the proline, glutathione, total phenolics, and flavonoid contents in Chinese flowering cabbage plants exposed to Pb stress compared with the control. Additionally, total glucosinolate content, phytochelatins (PCs), and non-protein thiols were effectively increased in plants grown under Pb regimes compared with the control plants. Overall, foliar application of liquiritoside can markedly alleviate Pb stress by restricting Pb translocation in Chinese flowering cabbage.

The moss flavone synthase I positively regulates the tolerance of plants to drought stress and UV-B radiation

Flavonoids are extensively distributed secondary metabolites in land plants. They play a critical role in plant evolution from aquatic to terrestrial and plant adaption to ultraviolet radiation. However, the downstream branching pathway of flavonoids and its regulatory mechanism in bryophytes, which are the most ancient of terrestrial plants, remain unclear. Here, a type I flavone synthase (PnFNSI) was characterized from the Antarctic moss Pohlia nutans. PnFNSI was primarily distributed in the cytoplasm, as detected by subcellular localization. PnFNSI could catalyze the conversion of naringenin to apigenin with an optimal temperature between 15 and 20 °C in vitro. Overexpression of PnFNSI in Arabidopsis alleviated the growth restriction caused by naringenin and accumulated apigenin product. PnFNSI-overexpressing plants showed enhanced plant tolerance to drought stress and UV-B radiation. PnFNSI also increased the enzyme activities and gene transcription levels of reactive oxygen species (ROS) scavengers, protecting plants against oxidative stress. Moreover, overexpression of PnFNSI enhanced the flavone biosynthesis pathway in Arabidopsis. Therefore, this moss FNSI-type enzyme participates in flavone metabolism, conferring protection against drought stress and UV-B radiation.

Contribution of two different Na+ transport systems to acquired salinity tolerance in rice

To elucidate the mechanisms of salt acclimation, physiological parameters of 70 rice varieties were compared under control and salt stress conditions after the acclimation treatment. The results indicated that some rice varieties had the ability to acclimatize to salt stress, exhibiting improved growth following the acclimation treatment under subsequent salinity stress compared to those without acclimation treatment. Conversely, some varieties exhibited reduced growth both with and without acclimation treatment under subsequent salinity stress. Acclimatized varieties had differential patterns of Na⁺ accumulation in the leaf blades because some varieties reduced Na⁺ accumulation under salinity stress, whereas others did not. Under salt stress, the acclimatized varieties with low Na⁺ accumulation in the leaf blades highly induced the expression of the OsHKT1;5 gene in the roots, which may contribute to Na⁺ exclusion from the shoots. On the other hand, the acclimatized varieties with high Na⁺ accumulation in the leaf blades exhibited higher induction of the OsNHX1 gene, whose gene product participates in the compartmentalization of Na⁺ into vacuoles. Thus, rice develops different mechanisms of salinity acclimation using two Na⁺ transport systems, and active regulation of Na⁺ transport at the transcription level may be involved in the salt acclimation process and enhance salinity tolerance.

Acquired salinity tolerance in rice: Plant growth dataset

This article describes the growth of 18 acclimatized and 11 non-acclimatized rice varieties grown in a hydroponic nutrient solution in a glasshouse. Four plants from each variety were grown under control conditions, salinity stress following control conditions (salinity), and salinity stress following acclimation (salinity/acclimation) conditions. Sampling was performed at the end of the salinity treatment (36 days of growth). Growth traits such as shoot and root biomass accumulation and lengths were measured for each variety, and the average was calculated using four replicates. This dataset may aid interested researchers in making comparisons with their data and further advance the research on the salinity acclimation process in rice.

Interactions between brown planthopper (Nilaparvata lugens) and salinity stressed rice (Oryza sativa) plant are cultivar-specific

Salinity stress triggers changes in plant morphology, physiology and molecular responses which can subsequently influence plant-insect interactions; however, these consequences remain poorly understood. We analyzed plant biomass, insect population growth rates, feeding behaviors and plant gene expression to characterize the mechanisms of the underlying interactions between the rice plant and brown planthopper (BPH) under salinity stress. Plant bioassays showed that plant growth and vigor losses were higher in control and low salinity conditions compared to high salinity stressed TN1 (salt-planthopper susceptible cultivar) in response to BPH feeding. In contrast, the losses were higher in the high salinity treated TPX (salt-planthopper resistant cultivar). BPH population growth was reduced on TN1, but increased on TPX under high salinity condition compared to the control. This cultivar-specific effect was reflected in BPH feeding behaviors on the corresponding plants. Quantification of abscisic acid (ABA) and salicylic acid (SA) signaling transcripts indicated that salinity-induced down-regulation of ABA signaling increased SA-dependent defense in TN1. While, up-regulation of ABA related genes in salinity stressed TPX resulted in the decrease in SA-signaling genes. Thus, ABA and SA antagonism might be a key element in the interaction between BPH and salinity stress. Taken together, we concluded that plant-planthopper interactions are markedly shaped by salinity and might be cultivar specific.

Constitutive overexpression of rice metallothionein-like gene OsMT-3a enhances growth and tolerance of Arabidopsis plants to a combination of various abiotic stresses

Metallothioneins (MT) are primarily involved in metal chelation. Recent studies have shown that MT proteins are also involved in the responses of plants to various environmental stresses. The rice metallothionein-like gene OsMT-3a is upregulated by salinity and various abiotic stressors. A DNA construct containing the complete OsMT-3a coding sequence cloned downstream to the CaMV35S promoter was transformed into Arabidopsis and homozygous single-copy transgenic lines were produced. Compared to wild-type plants, transgenic plants showed substantially increased salinity tolerance (NaCl), drought tolerance (PEG), and heavy metal tolerance (CdCl₂) as individual stresses, as well as different combinations of these stresses. Relevantly, under unstressed control conditions, vegetative growth of transgenic plants was also improved. The shoot Na⁺ concentration and hydrogen peroxide in transgenic plants were lower than those in wild-type plants. OsMT-3a-overexpressing Arabidopsis lines accumulated higher levels of Cd²⁺ in both shoots and roots following CdCl₂ treatment. In the transgenic MT-3a lines, increased activity of two major antioxidant enzymes, catalase and ascorbate peroxidase, was observed. Thus, rice OsMT-3a is a valuable target gene for plant genetic improvement against multiple abiotic stresses.

Exogenous vanillic acid enhances salt tolerance of tomato: Insight into plant antioxidant defense and glyoxalase systems

We investigated vanillic acid-induced salt tolerance in tomato by exploring the plant defense systems. Ten-d-old tomato (Solanum lycopersicum L. cv. Pusa Ruby) seedlings were treated with salt (NaCl; 150 mM) and vanillic acid (VA; 40 and 50 μM) separately and in combination with salt. Salinity restricted seedlings growth, biomass accumulation, chlorophyll and carotenoid contents. Salt-induced osmotic stress was indicated by lower leaf relative water content (RWC) and elevated proline (Pro) content, where higher Na⁺/K⁺ ratio indicated the ionic toxicity. Tomato seedlings went through oxidative damage due to acute reactive oxygen species (ROS) production and lipoxygenase (LOX) activity and confirmed by higher lipid peroxidation and membrane damage under salinity. Conversely, exogenous VA reduced osmotic and ionic toxicity in stressed-seedlings by enhancing the RWC and Pro level, and lowering Na⁺/K⁺ ratio, respectively. Exogenous VA up-regulated the components of antioxidant defense system in salt-treated seedlings resulted in the reduction of ROS production, LOX activity and membrane damage in stressed-seedlings. Additionally, VA application caused the reduction of toxic methylglyoxal accumulation under salt stress through the enhancement of glyoxalase system. Thus, VA-induced alleviation of osmotic, ionic and oxidative stresses leading to improve plant growth and chlorophyll synthesis in stressed-seedlings. So, VA significantly improves salinity tolerance and plant growth performance by involving the actions of plant antioxidant defense and glyoxalase systems.

Expression Analysis, Functional Marker Development and Verification of AgFNSI in Celery

Apigenin is one of the primary flavonoids in celery, which has a high medicinal value. Flavone synthase I (FNSI) is the last step enzyme in apigenin biosynthesis. In this study, the 1492 bp promoter sequence before AgFNSI initiation codon (ATG) of celery was obtained, which included methyl jasmonate (MeJA) responsive elements, light responsive elements, anaerobic induction elements and five MYB binding sites. AgFNSI was sensitive to temperature, UV-B, water deficit and MeJA. Comparative analysis of AgFNSI genome and promoter sequences among celery accessions with different apigenin content showed that there were four allelic variations in AgFNSI, and four accessions with high apigenin content belonged to AgFNSIa, and five accessions with low apigenin content belonged to AgFNSIc. Three pairs of dominant complementary markers were designed based on the single-nucleotile polymorphisms (SNPs) of the AgFNSIa and AgFNSIc genomes and promoter sequences. Three pairs of functional markers were validated by 112 celery accessions. The results showed that AFPA1/AFPB1 detected significant differences in apigenin content between different genotypes. Therefore, marker AFPA1/AFPB1 is associated with apigenin content in celery and could be used for the genetic improvement of apigenin content in celery.

Characterization of Na+ exclusion mechanism in rice under saline-alkaline stress conditions

This study was designed to elucidate the physiological responses of two rice genotypes to different pH levels under high saline stress. A salt-tolerant cultivar, FL478, and a salt-sensitive cultivar, IR29, were exposed to saline-alkaline solutions supplemented with 50 mM Na at pH 9 (severe), pH 8 (moderate), and pH 7 (mild) for three weeks. The results indicated that FL478 is relatively saline-alkaline tolerant compared to IR29, and this was evident from its higher dry mass production, lower Na⁺ concentration in the leaf blades, and maintenance of water balance under both mild and moderate saline-alkaline stress conditions. In both cultivars, Na⁺ concentrations in the leaf blades were considerably higher at pH 8 than at pH 7, indicating that high alkaline stress promoted Na⁺ accumulation under highly saline conditions. FL478 plants had lower Na⁺/K⁺ ratios in leaf blades and leaf sheaths than IR29 plants under saline-alkaline stress at both pH 7 and pH 8. To understand the mechanisms behind the difference in saline-alkaline tolerance between the two rice genotypes, transcript levels of the genes encoding Na⁺ transport proteins were analyzed. In response to mild and moderate saline-alkaline stress conditions, salt-tolerant FL478 had highly induced expression of the OsHKT1;5 gene in the roots, corresponding to lower Na⁺ accumulation in the leaf blades. Induction of high expression of the OsSOS1 gene in the roots of FL478 implied that Na may be effectively exported from cytosols to apoplasts in the roots resulting in sequestration of Na⁺ to outside of the roots and loading Na⁺ in xylem transpiration stream. On the other hand, the salt-sensitive IR29 had lower expression of the genes related to Na⁺ transporters, such as the OsHKT1;5 gene and the OsSOS1 gene, in the roots, leading to higher Na⁺ accumulation in the shoots. Expression of the determinant genes for alkaline tolerance, such as K⁺ and Fe acquisition and acidification of the rhizosphere was highly induced in FL478, but not in IR29. Thus, molecular analysis suggested that genes encoding Na⁺ transport proteins are involved in regulating Na⁺ transport under saline-alkaline stress in both salt-tolerant and salt-sensitive rice cultivars, and this is useful information for improving saline-alkaline tolerance traits of rice in the future.

Host Plant Salinity Stress Affects the Development and Population Parameters of Nilaparvata lugens (Hemiptera: Delphacidae)

Salinization is one of the most critical abiotic stress factors for crops and a rising setback in agro-ecosystems. Changes in weather, land usage, and the salinization of irrigation water are increasing soil salinity of many farmlands. Increased soil salinity alters the plant quality, which subsequently may trigger bottom-up effects on herbivorous insect. We examined the bottom-up effect of salinity stress on population parameters of the brown planthopper (BPH), Nilaparvata lugens through rice (Oryza sativa L.) plant. The results revealed that salinity interfered with egg hatching of BPH. The nymphal development period, adult longevity, and oviposition were also influenced by salinity. Notable differences appeared in the intrinsic growth rate (r), the finite increase rate (λ) and the net reproduction rate (R0) of BPH, and a concentration-dependent effect was detected. Although salinity adversely affected BPH development, population projection predicted a successful growth of the BPH population in a relatively short time under the treatment of low and medium levels of salinity (6, 8, and 10 dS/m of NaCl), whereas higher salt concentrations (12 and 14 dS/m) lead to significant fitness costs in BPH populations. Our study predicts that BPH could become a problem in areas with lower and medium salinity and that those planthoppers may exacerbate the negative effects of salinity for rice production. This study will provide valuable information for understanding the field abundance and distribution of BPH on saline rice field, thus contributing to the development of eco-friendly strategies to manage this pest in saline ecosystems.

Quercetin Mediated Salt Tolerance in Tomato through the Enhancement of Plant Antioxidant Defense and Glyoxalase Systems

Quercetin (Qu) is a strong antioxidant among the phenolic compounds having physiological and biochemical roles in plants. Hence, we have studied the Qu evolved protection against salinity in tomato (Solanum lycopersicum L.). Salinity caused ionic toxicity by increasing Na+ content in seedlings along with nutritional starvation of K+, Ca2+, and Mg2+. While osmotic stress was detected by higher free proline (Pro) content and lower leaf relative water content (LRWC) in salt-stressed seedlings. Salt toxicity also induced higher H2O2 generation, malondialdehyde (MDA) content and lipoxygenase (LOX) activity as a sign of oxidative stress. Tomato seedlings suffered from methylglyoxal (MG) toxicity, degradation of chlorophyll, along with lower biomass accumulation and growth due to salt exposure. However, Qu application under salinity resulted in lower Na+/K+ due to reduced Na+ content, higher LRWC, increased Pro, and reduction of H2O2 and MDA content, and LOX activity, which indicated alleviation of ionic, osmotic, and oxidative stress respectively. Quercetin caused oxidative stress, lessening through the strengthening of both enzymatic and non-enzymatic antioxidants. In addition, Qu increased glutathione S-transferase activity in salt-invaded seedlings, which might be stimulated reactive oxygen species (ROS) scavenging along with higher GSH content. As a result, toxic MG was detoxified in Qu supplemented salt-stressed seedlings by increasing both Gly I and Gly II activities. Moreover, Qu insisted on better plant growth and photosynthetic pigments synthesis in saline or without saline media. Therefore, exogenous applied Qu may become an important actor to minimize salt-induced toxicity in crops.

A Study on Tissue-Specific Metabolite Variations in Polygonum cuspidatum by High-Resolution Mass Spectrometry-Based Metabolic Profiling

Polygonum cuspidatum Sieb. et Zucc. is a traditional Chinese herbal medicine widely used to treat tussis, hepatitis and arthralgia. This study identified and quantitatively described the bioactive compounds in different P. cuspidatum tissues. Metabolic profiles of root, stem, leaf, flower, rhizome and seed were determined using high-resolution mass spectrometry in combination with multivariate analyses. In total, 53 metabolites, 8 reported for the first time in this species, were putatively identified and classified mainly as stilbenes, anthraquinones and flavonoids. A principal component analysis, cluster analysis and heatmap were used to depict the correlations between specimens and the relative abundance levels of these compounds in different plant tissues. An orthogonal partial least square discriminant analysis found that 13 metabolites showed distinct differences among the six plant tissues, making them potential discriminative tissue-identification markers. This study will provide guidance in comparing, selecting and exploiting the medicinal uses of different P. cuspidatum tissues.