Zinc stress affects ionome and metabolome in tea plants

Insights into the effects of anilofos on direct-seeded rice production system through untargeted metabolomics

Weed infestation is the major biological threat in direct-seeded rice production and can cause significant yield losses. The effective use of herbicides is particularly important in direct-seeded rice production. Anilofos, a pre-emergence herbicide, has been shown to be effective against the weed barnyardgrass. However, its impacts on crop yield and the direct-seeded rice production ecosystem remain underexplored. In this study, we conducted field trials and used untargeted metabolomics to investigate systemic effects of two different treatments (40 g/acre and 60 g/acre) on rice shoot and root as well as the rhizosphere soil during the critical tillering stage. Here, a total of 400 metabolites were determined in the crop and soil, with differential metabolites primarily comprising lipids and lipid-like molecules as well as phenylpropanoids and polyketides. Spearman correlation network analysis and a Zi-Pi plot revealed 7 key differential metabolites with significant topological roles, including succinic acid semialdehyde and riboflavin. KEGG pathway analysis showed that anilofos downregulated the amino acid metabolism while mainly promoted carbohydrate metabolism and secondary metabolites biosynthesis of the crop, which made minimal disruption on soil metabolism. Notably, we found 40 g/acre anilofos application could significantly improve the rice yield, potentially linked to the improved activity of flavonoid biosynthesis and starch and sucrose metabolism. This research provides a comprehensive evaluation of anilofos effects in the direct-seeded rice production system, offering new insights into optimizing herbicide use to improve agricultural sustainability and productivity.

Zinc/Iron-Regulated Transporter-like Protein CsZIP4 Enhances Zinc and Nitrogen Uptake and Alleviates Zinc Stresses with Nitrogen Supply in Camellia sinensis

Zinc (Zn) and nitrogen (N) are the two crucial nutrients for tea plant growth and development and contribute to the quality formation of tea fresh leaves. In this study, a zinc/iron-regulated transporter-like protein 4 gene (i.e., CsZIP4) was functionally characterized. Expression profiling showed that CsZIP4 could be induced by Zn stresses and a N deficiency. Heterologous expression of CsZIP4 in yeast revealed that CsZIP4 possessed the capacity for Zn transport but not ammonium. Moreover, CsZIP4 overexpression in Arabidopsis thaliana promoted Zn and N uptake and transport and contributed to alleviate Zn stresses by collaborating with N supply, which might be interrelated to the expression of N or Zn metabolism-related genes, such as AtNRT1.1 and AtZIP4. Additionally, CsZIP4 was localized in the plasma membrane and chloroplast, which was helpful in maintaining cellular homeostasis under a Zn excess. Furthermore, silencing of CsZIP4 in tea plants by virus-induced gene silencing increased the chlorophyll content but decreased the Zn content. Finally, the yeast one-hybrid assay demonstrated that CsbZIP2 bound to the CsZIP4 promoter. These results will shed light on the functions of CsZIP4 in the N and Zn interaction in tea plants.

Impact of zinc on arbuscular mycorrhizal-mediated nutrient acquisition in urban horticulture

A major barrier to sustainably improving food security for a growing global population is the availability of suitable space for growing crops. Urban areas offer a potential solution to increase availability of land, however, horticultural soils often accumulate zinc. These increased levels may affect the interactions between crops and soil microbes with potential implications for crop health and nutrition. Using radio-isotope tracing, we investigated the effect of urban environmentally relevant concentrations of zinc in soils on the nutrient exchange between arbuscular mycorrhizal fungi and pea plants. At higher concentrations of zinc, transfer of phosphorus from fungi to plants and the movement of carbon from plants to fungi was dramatically decreased. Our results suggest that while urban horticulture holds promise for sustainably enhancing local food production and addressing global food security, the unchecked presence of contaminants in these soils may pose a critical hurdle to realizing the potential of urban soils.

Metal tolerance protein CsMTP4 has dual functions in maintaining zinc homeostasis in tea plant

Plants have evolved a series of zinc (Zn) homeostasis mechanisms to cope with the fluctuating Zn in the environment. How Zn is taken up, translocated and tolerate by tea plant remains unknown. In this study, on the basis of RNA-Sequencing, we isolated a plasma membrane-localized Metal Tolerance Protein (MTP) family member CsMTP4 from Zn-deficient tea plant roots and investigated its role in regulation of Zn homeostasis in tea plant. Heterologous expression of CsMTP4 specifically enhanced the tolerance of transgenic yeast to Zn excess. Moreover, overexpression of CsMTP4 in tea plant hairy roots stimulated Zn uptake under Zn deficiency. In addition, CsMTP4 promoted the growth of transgenic Arabidopsis plants by translocating Zn from roots to shoots under Zn deficiency and conferred the tolerance to Zn excess by enhancing the efflux of Zn from root cells. Transcriptome analysis of the CsMTP4 transgenic Arabidopsis found that the expression of Zn metabolism-related genes were differentially regulated compared with wild-type plants when exposed to Zn deficiency and excess conditions. This study provides a mechanistic understanding of Zn uptake and translocation in plants and a new strategy to improve phytoremediation efficiency.

Do nanoparticles delivered to roots affect plant secondary metabolism? A comprehensive analysis in float seedling cultures of Hypericum perforatum L

Since nanoparticles (NPs) released into the environment from household or industrial wastes and applied directly on plants as agrochemicals can accumulate in the rhizosphere, it is imperative to understand how these NPs affect plant secondary metabolism upon their contact with the roots of intact plants. Here, the effects of Pd, Au, ZnO and Fe2O3 NPs on secondary metabolism were comprehensively investigated in Hypericum perforatum L float seedlings by analyzing 41 major secondary metabolites using ultra-performance liquid chromatography coupled with photodiode array, fluorescence detector and high-resolution mass spectrometry (UPLC-PDA-FLR-HRMS). The results showed that exposure of H. perforatum roots to Pd, Au, ZnO and Fe2O3 NPs rapidly led to fluctuations in the levels of secondary metabolites. Although these fluctuations did not correlate with NP type, concentration and duration of treatment, a total of 22 compounds were significantly altered by the NPs tested. In particular, 1 ppm Au increased the content of quercetin 3-(2″-acetylgalactoside), cadensin G and leutoskyrin by 5.02-, 2.12- and 2.58-fold, respectively after 24 h; 25 ppm Pd NPs led to a 2.1-fold increase in miquelianin content after 6 h; 50 ppm Fe2O3 NPs increased the level of furohyperforin by 3.09-fold and decreased the content of miquelianin 5.22-fold after 24 h and 50 ppm ZnO led to a 2.13-fold increase in hypericin after 48 h. These results emphasise the need to understand the intricate interplay between NPs and plant secondary metabolism in order to enable safer and efficient applications of NPs in agriculture.

Comprehensive applications of metabolomics on tea science and technology: Opportunities, hurdles, and perspectives

With the development of metabolomics analytical techniques, relevant studies have increased in recent decades. The procedures of metabolomics analysis mainly include sample preparation, data acquisition and pre-processing, multivariate statistical analysis, as well as maker compounds' identification. In the present review, we summarized the published articles of tea metabolomics regarding different analytical tools, such as mass spectrometry, nuclear magnetic resonance, ultraviolet-visible spectrometry, and Fourier transform infrared spectrometry. The metabolite variation of fresh tea leaves with different treatments, such as biotic/abiotic stress, horticultural measures, and nutritional supplies was reviewed. Furthermore, the changes of chemical composition of processed tea samples under different processing technologies were also profiled. Since the identification of critical or marker metabolites is a complicated task, we also discussed the procedure of metabolite identification to clarify the importance of omics data analysis. The present review provides a workflow diagram for tea metabolomics research and also the perspectives of related studies in the future.

Zinc and nano zinc mediated alleviation of heavy metals and metalloids in plants: an overview

Heavy metals and metalloids (HMs) contamination in the environment has heightened recently due to increasing global concern for food safety and human livability. Zinc (Zn2+ ) is an important nutrient required for the normal development of plants. It is an essential cofactor for the vital enzymes involved in various biological mechanisms of plants. Interestingly, Zn2+ has an additional role in the detoxification of HMs in plants due to its unique biochemical-mediating role in several soil and plant processes. During any exposure to high levels of HMs, the application of Zn2+ would confer greater plant resilience by decreasing oxidative stress, maintaining uptake of nutrients, photosynthesis productivity and optimising osmolytes concentration. Zn2+ also has an important role in ameliorating HMs toxicity by regulating metal uptake through the expression of certain metal transporter genes, targeted chelation and translocation from roots to shoots. This review examined the vital roles of Zn2+ and nano Zn in plants and described their involvement in alleviating HMs toxicity in plants. Moving forward, a broad understanding of uptake, transport, signalling and tolerance mechanisms of Zn2+ /zinc and its nanoparticles in alleviating HMs toxicity of plants will be the first step towards a wider incorporation of Zn2+ into agricultural practices.

Utilizing X-ray fluorescence (XRF) method to evaluate the content of metal elements in soil and their effects on the total phenolic and flavonoid contents of some medicinal plants

Soil factors, especially metal elements in the soil, play a significant role in forming and accumulating secondary metabolites, which determine the medicinal properties of medicinal herbs. In this study, the concentrations of some metal elements (K, Mn, Fe, Cu, Zn, and Cr) in Cam Mountain and Tinh Bien Town, An Giang Province, Vietnam, were determined using the XRF method. We simultaneously determined the total phenolic and flavonoid content of some medicinal herbs collected from the collected soil sample areas, thereby assessing the influence of these elements on the formation of secondary metabolites in medicinal plants. The results showed that K, Mn, and Cr were mainly concentrated in the topsoil and transition layers; Fe and Cu elements tended to concentrate in the transition layer and the subsoil when surveying the soil profile. K, Mn, Cu, and Cr concentrations were more focused in Tinh Bien area, while Fe and Zn had higher concentrations at Cam Mountain. Additionally, results from evaluating the relationship between the content of the elements in the soil and the content of two active compounds also showed the correlation regression model between Zn and flavonoid expression by level 4 at the 5% significance level. Thus, the nonlinear model is suitable for evaluating the relationship between the content of metal elements in the soil and the active compound in medicinal plants.

Metabolomic analysis reveals the molecular responses to copper toxicity in rice (Oryza sativa)

Copper (Cu) is one of the essential microelements and widely participates in various pathways in plants, but excess Cu in plant cells could induce oxidative stress and harm plant growth. Rice (Oryza sativa) is a main crop food worldwide. The molecular mechanisms of rice in response to copper toxicity are still not well understood. In this study, two-week-old seedlings of the rice cultivar Nipponbare were treated with 100 μM Cu²⁺ (CuSO₄) in the external solution for 10 days. Physiological analysis showed that excess Cu significantly inhibited the growth and biomass of rice seedlings. After Cu treatment, the contents of Mn and Zn were significantly reduced in the roots and shoots, while the Fe content was significantly increased in the roots. Meanwhile, the activities of antioxidant enzymes including SOD and POD were dramatically enhanced after Cu treatment. Based on metabolomic analysis using liquid chromatography-tandem mass spectrometry (LC-MS/MS) methods, 695 metabolites were identified in rice roots. Among these metabolites, 123 metabolites were up-regulated and 297 were down-regulated, respectively. The differential metabolites (DMs) include carboxylic acids and derivatives, benzene and substituted derivatives, carbonyl compounds, cinnamic acids and derivatives, fatty acyls and organ nitrogen compounds. KEGG analysis showed that these DMs were mainly enriched in TCA cycle, purine metabolism and starch and sucrose metabolism pathways. Many intermediates in the TCA cycle and purine metabolism were down-regulated, indicating a perturbed carbohydrate and nucleic acid metabolism. Taken together, the present study provides new insights into the mechanism of rice roots to Cu toxicity.

Effect of Green Synthesized ZnO-NPs on Growth, Antioxidant System Response and Bioactive Compound Accumulation in Echinops macrochaetus, a Potential Medicinal Plant, and Assessment of Genome Size (2C DNA Content)

Echinops macrochaetus is a medicinal plant that can be used to cure various diseases. In the present study, plant-mediated zinc oxide nanoparticles (ZnO-NPs) were synthesized using an aqueous leaf extract of the medicinal plant Heliotropium bacciferum and characterized using various techniques. E. macrochaetus was collected from the wild and identified using the internal transcribed spacer sequence of nrDNA (ITS-nrDNA), which showed the closeness to its related genus in a phylogenetic tree. The effect of synthesized biogenic ZnO-NPs was studied on E. macrochaetus in a growth chamber for growth, bioactive compound enhancement and antioxidant system response. The irrigation of plants at a low concentration of ZnO-NPs (T1 = 10 mg/L) induced more growth in terms of biomass, chlorophyll content (273.11 µg/g FW) and carotenoid content (135.61 µg/g FW) than the control and other treatments (T2-20 mg/L and T3-40 mg/L). However, the application of a high concentration of ZnO-NPs (20 and 40 mg/L) increased the level of antioxidant enzymes (SOD, APX and GR), total crude and soluble protein, proline and TBARS contents. The accumulations of the compounds quercetin-3-β-D-glucoside, luteolin 7-rutinoside and p-coumaric acid were greater in the leaf compared to the shoot and root. A minor variation was observed in genome size in treated plants as compared to the control group. Overall, this study revealed the stimulatory effect of phytomediated ZnO-NPs, which act as bio-stimulants/nano-fertilizers as revealed by more biomass and the higher production of phytochemical compounds in different parts of the E. macrochaetus.

Data Science and Plant Metabolomics

The study of plant metabolism is one of the most complex tasks, mainly due to the huge amount and structural diversity of metabolites, as well as the fact that they react to changes in the environment and ultimately influence each other. Metabolic profiling is most often carried out using tools that include mass spectrometry (MS), which is one of the most powerful analytical methods. All this means that even when analyzing a single sample, we can obtain thousands of data. Data science has the potential to revolutionize our understanding of plant metabolism. This review demonstrates that machine learning, network analysis, and statistical modeling are some techniques being used to analyze large quantities of complex data that provide insights into plant development, growth, and how they interact with their environment. These findings could be key to improving crop yields, developing new forms of plant biotechnology, and understanding the relationship between plants and microbes. It is also necessary to consider the constraints that come with data science such as quality and availability of data, model complexity, and the need for deep knowledge of the subject in order to achieve reliable outcomes.

Diversity and expression analysis of ZIP transporters and associated metabolites under zinc and iron stress in Capsicum

The members of ZRT, IRT-like protein (ZIP) family are involved in the uptake and transportation of several metal ions. Here, we report a comprehensive identification of ZIP transporter genes from Capsicum annuum, C. chinense, and C. baccatum, and their expression analysis under Zn and Fe stress. Changes in root morphology and differential accumulation of several metabolites from sugars, amino acids, carboxylic acids, and fatty acids in root and leaf tissues of plants in the absence of Zn and Fe were observed. Further, metabolites such as L-aspartic acid, 2-ketoglutaric acids, β-L-fucopyranose, quininic acid, chlorogenic acid, and aucubin were significantly upregulated in root and leaf tissues under Zn/Fe deprived conditions. qRT-PCR analysis of 17 CaZIPs in different tissues revealed tissue-specific expression of CaZIP1-2, CaZIP4-8, CaZIP13, and CaZIP16-17 under normal conditions. However, the absence of Zn and Fe significantly induced the expression of CaZIP4-5, CaZIP7-9, and CaZIP14 genes in root and leaf tissues. Additionally, in the absence of Fe, upregulation of CaZIP4-5 and CaZIP8 and increased uptake of mineral elements Cu, Zn, Mg, P, and S were observed in roots, suggesting their potential role in metal-ion uptake in Capsicum. The identified genes provide the basis for future studies of mineral uptake and their biofortification to increase the nutritional values in Capsicum.

Integrated Metabolomic and Transcriptomic Analysis Reveals That Amino Acid Biosynthesis May Determine Differences in Cold-Tolerant and Cold-Sensitive Tea Cultivars

Cold stress is one of the major abiotic stresses limiting tea production. The planting of cold-resistant tea cultivars is one of the most effective measures to prevent chilling injury. However, the differences in cold resistance between tea cultivars remain unclear. In the present study, we perform a transcriptomic and metabolomic profiling of Camellia sinensis var. "Shuchazao" (cold-tolerant, SCZ) and C. sinensis var. assamica "Yinghong 9" (cold-sensitive, YH9) during cold acclimation and analyze the correlation between gene expression and metabolite biosynthesis. Our results show that there were 51 differentially accumulated metabolites only up-regulated in SCZ in cold-acclimation (CA) and de-acclimation (DA) stages, of which amino acids accounted for 18%. The accumulation of L-arginine and lysine in SCZ in the CA stage was higher than that in YH9. A comparative transcriptomic analysis showed an enrichment of the amino acid biosynthesis pathway in SCZ in the CA stage, especially "arginine biosynthesis" pathways. In combining transcriptomic and metabolomic analyses, it was found that genes and metabolites associated with amino acid biosynthesis were significantly enriched in the CA stage of SCZ compared to CA stage of YH9. Under cold stress, arginine may improve the cold resistance of tea plants by activating the polyamine synthesis pathway and CBF (C-repeat-binding factor)-COR (cold-regulated genes) regulation pathway. Our results show that amino acid biosynthesis may play a positive regulatory role in the cold resistance of tea plants and assist in understanding the cold resistance mechanism differences among tea varieties.

Metabolomic Changes as Key Factors of Green Plant Regeneration Efficiency of Triticale In Vitro Anther Culture

Green plant regeneration efficiency (GPRE) via in vitro anther culture results from biochemical pathways and cycle dysfunctions that may affect DNA and histone methylation, with gene expression influencing whole cell functioning. The reprogramming from gametophytic to sporophytic fate is part of the phenomenon. While DNA methylation and sequence changes related to the GPRE have been described, little attention was paid to the biochemical aspects of the phenomenon. Furthermore, only a few theoretical models that describe the complex relationships between biochemical aspects of GPRE and the role of Cu(II) ions in the induction medium and as cofactors of enzymatic reactions have been developed. Still, none of these models are devoted directly to the biochemical level. Fourier transform infrared (FTIR) spectroscopy was used in the current study to analyze triticale regenerants derived under various in vitro tissue culture conditions, including different Cu(II) and Ag(I) ion concentrations in the induction medium and anther culture times. The FTIR spectra of S-adenosyl-L-methionine (SAM), glutathione, and pectins in parallel with the Cu(II) ions, as well as the evaluated GPRE values, were put into the structural equation model (SEM). The data demonstrate the relationships between SAM, glutathione, pectins, and Cu(II) in the induction medium and how they affect GPRE. The SEM reflects the cell functioning under in vitro conditions and varying Cu(II) concentrations. In the presented model, the players are the Krebs and Yang cycles, the transsulfuration pathway controlled by Cu(II) ions acting as cofactors of enzymatic reactions, and the pectins of the primary cell wall.

Zinc toxicity response in Ceratoides arborescens and identification of CaMTP, a novel zinc transporter

Zinc (Zn) is an essential micronutrient for several physiological and biochemical processes. Changes in soil Zn levels can negatively affect plant physiology. Although the mechanism of Zn nutrition has been studied extensively in crops and model plants, there has been little research on steppe plants, particularly live in alkaline soils of arid and semiarid regions. Ceratoides arborescens is used in arid and semiarid regions as forage and ecological restoration germplasm, which is studied can enrich the mechanism of Zn nutrition. The plants were exposed to three different Zn treatments, Zn-deficient (-Zn 0 mM L^-1), Zn-normal (Control, 0.015 mM L^-1), and Zn-excess (+Zn, 0.15 mM L^-1), for 3 weeks. Individual biomass, ion concentrations, photosynthetic system, and antioxidant characteristics were measured. High Zn supply significantly decreased plant biomass and induced chlorosis and growth defects and increased Zn concentration but decreased Fe and Ca concentrations, unlike in controls (p < 0.05). High Zn supply also reduced plant chlorophyll content, which consequently decreased the photosynthesis rate. Increased concentrations of malondialdehyde and soluble sugar and activities of peroxidase and superoxide dismutase could resist the high-level Zn stress. In contrast, low Zn supply did not affect plant growth performance. We also identified a novel protein through RNA transcriptome analysis, named CaMTP, that complemented the sensitivity of a yeast mutant to excessive Zn, which was found to be localized to the endoplasmic reticulum through transient gene expression in Nicotiana benthamiana. The gene CaMTP identified to be highly sensitive to Zn stress is a potential candidate for overcoming mineral stress in dicot crop plants.

Dissection of Crop Metabolome Responses to Nitrogen, Phosphorus, Potassium, and Other Nutrient Deficiencies

Crop growth and yield often face sophisticated environmental stresses, especially the low availability of mineral nutrients in soils, such as deficiencies of nitrogen, phosphorus, potassium, and others. Thus, it is of great importance to understand the mechanisms of crop response to mineral nutrient deficiencies, as a basis to contribute to genetic improvement and breeding of crop varieties with high nutrient efficiency for sustainable agriculture. With the advent of large-scale omics approaches, the metabolome based on mass spectrometry has been employed as a powerful and useful technique to dissect the biochemical, molecular, and genetic bases of metabolisms in many crops. Numerous metabolites have been demonstrated to play essential roles in plant growth and cellular stress response to nutrient limitations. Therefore, the purpose of this review was to summarize the recent advances in the dissection of crop metabolism responses to deficiencies of mineral nutrients, as well as the underlying adaptive mechanisms. This review is intended to provide insights into and perspectives on developing crop varieties with high nutrient efficiency through metabolite-based crop improvement.

Transcriptome analysis reveals the mechanism of zinc ion-mediated plant resistance to TMV in Nicotiana benthamiana

Zinc ions (Zn2+) are used to promote plant growth and treat multiple diseases. However, it is still unclear which pathways in plants respond to Zn2+. In this study, we found that supplying (CH3COO)2Zn can effectively delay tobacco mosaic virus (TMV) replication and movement in Nicotiana benthamiana. To further understand the regulatory mechanism of antiviral activity mediated by Zn2+, we examined the transcriptomic changes of leaves treated with Zn2+. Three days after treatment, 7575 differential expression genes (DEGs) were enriched in the Zn2+ treatment group compared with the control group. Through GO and KEGG analysis, the pathway of phosphatidylinositol signaling system and inositol phosphate metabolism were significantly enriched after treated with Zn2+, and a large number of ethylene-responsive transcription factors (ERFs) involved in inositol phosphate metabolism were found to be enriched. We identified ERF5 performed a positive effect on plant immunity. Our findings demonstrated that Zn2+-mediated resistance in N. benthamiana activated signal transduction and regulated the expression of resistance-related genes. The results of the study uncover a global view of mRNA changes in Zn2+-mediated cellular processes involved in the competition between plants and viruses.

Regulation of biosynthesis of the main flavor-contributing metabolites in tea plant (Camellia sinensis): A review

In the process of adapting to the environment, tea plants (Camellia sinensis) endow tea with unique flavor and health functions, which should be attributed to secondary metabolites, including catechins, L-theanine, caffeine and terpene volatiles. Since the content of these flavor-contributing metabolites are mainly determined by the growth of tea plant, it is very important to understand their alteration and regulation mechanisms. In the present work, we first summarize the distribution, change characteristics of the main flavor-contributing metabolites in different cultivars, organs and under environmental stresses of tea plant. Subsequently, we discuss the regulating mechanisms involved in the biosynthesis of these metabolites based on the existing evidence. Finally, we propose the remarks and perspectives on the future study relating flavor-contributing metabolites. This review would contribute to the acceleration of research on the characteristic secondary metabolites and the breeding programs in tea plants.

Impact of nanoparticles and their ionic counterparts derived from heavy metals on the physiology of food crops

Heavy metals and their engineered nanoparticle (NP) counterparts are emerging contaminants in the environment that have captured the attention of researchers worldwide. Although copper, iron, zinc and manganese are essential micronutrients for food crops, higher concentrations provoke several physiological and biochemical alterations that in extreme cases can lead to plant death. The effects of heavy metals on plants have been studied but the influence of nanoparticles (NPs) derived from these heavy metals, and their comparative effect is less known. In this critical review, we have found similar impacts for copper and manganese ionic and NP counterparts; in contrast, iron and zinc NPs seem less toxic for food crops. Although these nutrients are metals that can be dissociated in water, few authors have conducted joint ionic state and NP assays to evaluate their comparative effect. More efforts are thus required to fully understand the impact of NPs and their ion counterparts at the physiological, metabolic and molecular dimensions in crop plants.

Identification and expression analysis of the ZRT, IRT-like protein (ZIP) gene family in Camellia sinensis (L.) O. Kuntze

The ZRT, IRT-like protein (ZIP) family plays an essential role in the homeostasis of zinc and iron in plants. However, studies on this family are mainly limited to model species. Here, 12 CsZIPs were identified and investigated the function in Camellia sinensis, being named CsZIP1-12 and divided into four different groups based on phylogenetic relationships. These CsZIPs contained 2-9 TMDs and other conserved motifs for ZIP proteins. And CsZIPs were located in cell membrane, excepting for CsZIP4 and CsZIP6. The expression of CsZIPs were different in varieties and organs of tea plants. They were involved in the response process of abiotic stresses, such as NaCl, drought, cold and exogenous Me-JA. In addition, 31 types of promoter elements were identified in the CsZIPs, including core promoters, light responsiveness, stress responsive and other elements. The CsZIP1, CsZIP2, CsZIP4, CsZIP5, CsZIP6, CsZIP11 and CsZIP12 could be induced by zinc deficiency and 50 μM Zn treatment, but CsZIP7 and CsZIP8 were up regulated by 300 μM Zn. Heterogeneous complementation analysis showed that CsZIP1, CsZIP2, CsZIP7 and CsZIP8 could complement the Zn sensitivity of △zrc1cot1 yeast double mutant. There was a positive correlation between the expression of CsZIPs and secondary metabolites in tea plant. Together, our analysis of CsZIPs could provide comprehensive insights on the structure and function of this protein family in the regulation of zinc and ion homeostasis in the tea plant.

Advances in "Omics" Approaches for Improving Toxic Metals/Metalloids Tolerance in Plants

Food safety has emerged as a high-urgency matter for sustainable agricultural production. Toxic metal contamination of soil and water significantly affects agricultural productivity, which is further aggravated by extreme anthropogenic activities and modern agricultural practices, leaving food safety and human health at risk. In addition to reducing crop production, increased metals/metalloids toxicity also disturbs plants' demand and supply equilibrium. Counterbalancing toxic metals/metalloids toxicity demands a better understanding of the complex mechanisms at physiological, biochemical, molecular, cellular, and plant level that may result in increased crop productivity. Consequently, plants have established different internal defense mechanisms to cope with the adverse effects of toxic metals/metalloids. Nevertheless, these internal defense mechanisms are not adequate to overwhelm the metals/metalloids toxicity. Plants produce several secondary messengers to trigger cell signaling, activating the numerous transcriptional responses correlated with plant defense. Therefore, the recent advances in omics approaches such as genomics, transcriptomics, proteomics, metabolomics, ionomics, miRNAomics, and phenomics have enabled the characterization of molecular regulators associated with toxic metal tolerance, which can be deployed for developing toxic metal tolerant plants. This review highlights various response strategies adopted by plants to tolerate toxic metals/metalloids toxicity, including physiological, biochemical, and molecular responses. A seven-(omics)-based design is summarized with scientific clues to reveal the stress-responsive genes, proteins, metabolites, miRNAs, trace elements, stress-inducible phenotypes, and metabolic pathways that could potentially help plants to cope up with metals/metalloids toxicity in the face of fluctuating environmental conditions. Finally, some bottlenecks and future directions have also been highlighted, which could enable sustainable agricultural production.

Effect of Graft and Nano ZnO on Nutraceutical and Mineral Content in Bell Pepper

The objective of this experiment was to evaluate the effects of grafting, zinc oxide nanoparticles (ZnO NPs), and their interaction on the nutritional composition of bell pepper plants. The treatments evaluated included grafted and non-grafted pepper plants with four concentrations of ZnO NPs (0, 10, 20, 30 mg L-1) applied to the foliage. The following parameters were evaluated: content of N, P, K+, Ca2+, Mg2+, Mn2+, Zn2+, Fe2+, Cu2+, total antioxidants, ascorbic acid, total phenols, glutathione, total proteins, fruit firmness, and total soluble solids. Grafting increased the content of N 12.2%, P 15.9%, K+ 26.7%, Mg2+ 20.3%, Mn2+ 34.7%, Zn2+ 19.5%, Fe2+ 18.2%, Cu2+ 11.5%, antioxidant capacity 2.44%, ascorbic acid 4.63%, total phenols 1.33%, glutathione 7.18%, total proteins 1.08%, fruit firmness 8.8%. The application of 30 mg L-1 ZnO NPs increased the content of N 12.3%, P 25.9%, Mg2+ 36.8%, Mn2+ 42.2%, Zn2+ 27%, Fe2+ 45%, antioxidant activity 13.95%, ascorbic acid 26.77%, total phenols 10.93%, glutathione 11.46%, total proteins 11.01%, and fruit firmness 17.7% compared to the control. The results obtained demonstrate the influence of the use of grafts and ZnO NPs as tools that could improve the quality and nutrient content in fruits of bell pepper crops.

Foliar application of glycinebetaine and Zn fertilizer improves both the apparent and functional qualities of albino tea [Camellia sinensis (L.) O. Kuntze]

With Zn deficiency increasing in the global population, functional plant food (including tea) can help to fill the nutrition gap that the main crops cannot meet. Glycinebetaine (GB), an important bioactive substance with a wide range of natural sources, has received limited attention towards its effects on Zn biofortification and the quality of tea. The Zn enrichment and metabolite responses of albino tea [cv. White leaf No. 1 (WL-1)] to the foliar application of GB, Zn, and their combination (Zn + GB) were investigated in a field experiment. The result indicated that the 100-buds weight, total N, Zn, Thea, and total amino acid content in the young leaves of WL-1 with Zn2 + GB2 treatment were significantly increased, whereas the Chla contents were decreased (p < 0.05). The total catechins and CAF contents of Zn2 + GB2 treatment were lower than those of other treatments, with significance (p < 0.05). Multivariate analysis and general quantitative analysis returned complementary results, revealing that Zn2 + GB2 treatment was better for the apparent and functional quality of WL-1. The more theanine and Zn, limited chlorophyll, catechin, and caffeine contributed to the quality improvement, as well as to maintaining the leaf albinistic characteristics, inhibiting astringency and bitterness, exerting flavor and umami, and improving the ultimate beneficial functions. The combined application of Zn and GB is a promising practice for Zn biofortification and for the quality improvement of tea, with spraying 750 L ha^-1 of 2.0 g L^-1 Zn fertilizer and 3.2 g L^-1 GB mixture recommended.

Isolation, Characterization of Zn Solubilizing Bacterium (Pseudomonas protegens RY2) and its Contribution in Growth of Chickpea (Cicer arietinum L) as Deciphered by Improved Growth Parameters and Zn Content

Background: Zinc is an essential micronutrient required for optimum plant growth. Zinc-solubilizing bacteria convert applied inorganic zinc to available forms that could be used by plants. Research design: In present study, experiments were conducted to isolate, characterize, and evaluate Zn solubilization potential of different bacteria. Results: Among 10 isolated strains, Pseudomonas protegens (RY2, MF351762) was found to be the most promising strain having zinc-solubilizing potential on 4 different insoluble zinc sources. In quantitative assay, Zn solubilization by RY2 was significantly higher than other strains at different incubation time. P. protegens RY2 was selected (based on zinc solubilizing and plant growth promoting activities like P solubilization and ACC deaminase) for plant experiments. Meanwhile, available Zn release rate in soil was determined at day 10 of incubation. Chickpea seeds were inoculated with RY2 strain and ZnO is used as zinc source. Growth parameters and quantifying zinc content of shoot and root using atomic absorption spectrophotometer were determined. Enhanced shoot and root dry weights and lengths were observed in chickpea plants compared to control. Maximum increase of 44%, 67%, and 75% in T2 (Soil + RY2), T5 (Soil + ZnO + RY2), and T7 (Soil + manure + ZnO + RY2), respectively, was found in shoot length compared to control (T1). Conclusion: The study indicated that zinc-solubilizing RY2 strain possesses potential for enhanced Zn in soil so it would allow reduced inorganic Zn application.

Zinc toxicity in plants: a review

This review highlights the most recent updated information available about Zn phytotoxicity at physiological, biochemical and molecular levels, uptake mechanisms as well as excess Zn homeostasis in plants. Zinc (Zn) is a natural component of soil in terrestrial environments and is a vital element for plant growth, as it performs imperative functions in numerous metabolic pathways. However, potentially noxious levels of Zn in soils can result in various alterations in plants like reduced growth, photosynthetic and respiratory rate, imbalanced mineral nutrition and enhanced generation of reactive oxygen species. Zn enters into soils through various sources, such as weathering of rocks, forest fires, volcanoes, mining and smelting activities, manure, sewage sludge and phosphatic fertilizers. The rising alarm in environmental facet, as well as, the narrow gap between Zn essentiality and toxicity in plants has drawn the attention of the scientific community to its effects on plants and crucial role in agricultural sustainability. Hence, this review focuses on the most recent updates about various physiological and biochemical functions perturbed by high levels of Zn, its mechanisms of uptake and transport as well as molecular aspects of surplus Zn homeostasis in plants. Moreover, this review attempts to understand the mechanisms of Zn toxicity in plants and to present novel perspectives intended to drive future investigations on the topic. The findings will further throw light on various mechanisms adopted by plants to cope with Zn stress which will be of great significance to breeders for enhancing tolerance to Zn contamination.

Fullerenol changes metabolite responses differently depending on the iron status of cucumber plants

The unique properties of carbon-based nanomaterials, including fullerenol, have attracted great interest in agricultural and environmental applications. Iron (Fe) is an essential micronutrient for major metabolic processes, for which a shortage causes chlorosis and reduces the yield of many crops cultivated worldwide. In the current study, the metabolic responses of Cucumis sativus (a Strategy I plant) to fullerenol treatments were investigated depending on the Fe status of plants. Cucumber plants were grown hydroponically, either with [+FeII (ferrous) and +FeIII (ferric)] or in Fe-free (-FeII and -FeIII) nutrient solution, with (+F) or without (-F) a fullerenol supply. Iron species-dependent effects were observed in either Fe-fed or Fe-starved plants, with alteration of metabolites involved in the metabolism of carbohydrates, amino acids, organic acids, lipophilic compounds. Metabolic perturbations triggered by fullerenol in the FeIII-treated plants were in the opposite kind from those in the FeII-treated plants. Whereas in the FeIII-fed plants, fullerenol activated the metabolisation of carbohydrates and amino acids, in the FeII-fed plants, fullerenol activated the metabolisation of lipophilic compounds and repressed the metabolisation of carbohydrates and amino acids. In FeIII-deficient plants, fullerenol stimulated the metabolism of C3 carboxylates and lipophilic compounds while repressing the metabolism of amino acids, hexoses and dicarboxylates, while in FeII-deficient plants, activations of the metabolism of amino acids and dicarboxylates and repression of sterol metabolism by fullerenol were observed. The results indicated that the valence state of Fe sources is of importance for re-programming metabolome responses in cucumber to fullerenol either in Fe-sufficient or Fe-deficient conditions. These investigations are significant for understanding fullerenol interactions and risk assessment in plants with different Fe statuses.

Zinc affects the physiology and medicinal components of Dendrobium nobile Lindl

The growth of Dendrobium nobile is often influenced by zinc. Here, D. nobile was regularly sprayed with different concentrations (0, 50, 100, 200, 400, 800, 1000, 2000 μmol L^-1) of zinc to study its effect on the growth and biosynthesis of medicinal components. Samples were taken at 0, 7, 14, and 21 days to detect physiological and medicinal components. The results showed that the net photosynthetic rate, transpiration rate, stomatal conductance, and Chl A and Chl B levels of leaves first increased and then decreased as the concentration of zinc increased. At 400 μmol L^-1 concentration, these parameters reached their maximum values. Thus, a certain dose of zinc could promote the photosynthesis of D. nobile. There was an obvious increase in the synthesis of superoxide dismutase (SOD), while the content of ascorbate peroxidase and ascorbic acid (AsA) were the highest after treatment with 400 μmol L^-1 zinc. Maximum levels of polysaccharides and polyphenols were observed on day 7 and 14, respectively, at a zinc concentration of 400 μmol L^-1. These results suggest that exogenous zinc may promote the accumulation of medicinal components in D. nobile. It was also found that polysaccharides could combine well with zinc to form a polysaccharide-zinc chelate and transform inorganic zinc into organic form, which is stored in the form of polysaccharide-Zn and is known to reduce the damage induced by Zn stress.

Non-targeted metabolomics reveal the impact of phenanthrene stress on root exudates of ten urban greening tree species

Different root exudations can modify the bioavailability of persistent organic pollutants (POPs). Among these exudations, the low molecular weight organic acids play an imperative role in this process. The study was conducted to analyze the effect of phenanthrene (PHE) stress on root exudation variations and changes in its chemical composition in ten urban greening tree species, namely Loropetalum chinense, Gardenia ellis, Photinia fraseri, Ligustrum japonicum, Rhododendron simsii, Osmanthus fragrans, Gardenia jasminoides, Buxus sinica, Camellia sasanqua, and Euonymus japonicas. The experiment was carried out in three PHE concentration treatments (0 mg kg^-1 (CK), 200 mg kg^-1 (PHE_L), 2000 mg kg^-1 (PHE_H)). The root exudates were collected and analyzed by GC-MS method. In total, 673 compounds were identified either with high or low abundance among all species and treatments. Compounds identified in CK, PHE_L, and PHE_H were 240, 180, and 256, respectively. The results illustrated that carbohydrates, phenols, and esters were the dominant compounds, accounted for more than 92%. Principal component analysis depicted that tree species grown in PHE_H showed obvious alteration in compounds of root exudation, whereas little difference was noticed between PHE_L and CK. Phenols (80%) were the most abundant, while nitriles contributed a small portion. Moreover, among all species, R. simsii released the maximum number of compounds, and L. japonicum released the least number of compounds accounting for 89 and 46, respectively. The results achieved here to illustrate that plant type, and PHE stress can significantly change the concentrations and species of root exudates. This study provides the scientific reference for understanding the phenanthrene responsive changes in root exudates and phytoremediation of polycyclic aromatic hydrocarbons (PAHs), as well as a screening of urban greening tree species.

Biochemical mechanisms of rhizospheric Bacillus subtilis-facilitated phytoextraction by alfalfa under cadmium stress - Microbial diversity and metabolomics analyses

The effects of Bacillus subtilis inoculation on the growth and Cd uptake of alfalfa were evaluated in this research using pot experiments, and the relevant biochemical mechanisms were first investigated by combined microbial diversity and nontarget metabolomics analyses. The results indicated that inoculation with alfalfa significantly decreased the amount of plant malondialdehyde (MDA) and improved the activities of plant antioxidant enzymes and soil nutrient cycling-involved enzymes, thereby promoting biomass by 29.4%. Inoculation also increased Cd bioavailability in rhizosphere soil by 12.0% and Cd removal efficiency by 139.3%. The biochemical mechanisms included enhanced bacterial diversity, transformed microbial community composition, regulated amounts of amino acids, fatty acids, carbohydrates, flavonoids and phenols in rhizosphere soil metabolites, and modulations of the corresponding Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. These responses were beneficial to microbial activity, nutrient cycling, and Cd mobilization, detoxification, and decontamination by alfalfa in soil. This study, especially the newly identified differential metabolites and metabolic pathways, provides new insights into mechanism revelation and strategy development in microbe-assisted phytomanagement of heavy metal-contaminated soils.

Metabolics and ionomics responses of tea leaves (Camellia sinensis (L.) O. Kuntze) to fluoride stress

Tea plant (Camellia sinensis (L.) O. Kuntze) is known to accumulate high concentrations of fluoride (F) in its leaves; however, the underlying mechanism of F accumulation remains unclear. The main objective of this study was to investigate the homeostatic self-defense mechanisms of tea leaves to F supplementation (0, 5, 20, and 50 mgL^-1) by metabolomics and ionomics. We identified a total of 96 up-regulated and 40 down-regulated metabolites in tea leaves treated with F. Of these different compounds, minor polypeptides, carbohydrates and amino acids played valuable roles in the F-tolerating mechanism of tea plant. After F treatments, the concentrations of sodium (Na), ferrum (Fe), manganese (Mn), and molybdenum (Mo) were significantly increased in tea leaves, whereas the aluminum (Al) was decreased. These findings suggest that the ionic balance and metabolites are attributable to the development of F tolerance, providing new insight into tea plant adaptation to F stress.

Survival strategies based on the hydraulic vulnerability segmentation hypothesis, for the tea plant [Camellia sinensis(L.) O. Kuntze] in long-term drought stress condition

Tea plants are important economic perennial crops that can be negatively impacted by drought stress (DS). However, their survival strategies in long-term DS conditions and the accumulation and influence of metabolites and mineral elements (MEs) in their organs, when facing hydraulic vulnerability segmentation, require further investigation. The MEs and metabolites in the leaf, stem, and root after long-term DS (20 d) were examined here, using inductively coupled plasma optical emission spectrometry (ICP-OES) and liquid chromatograph-mass spectrometry (LC-MS). The accumulation patterns of 116 differentially accumulated metabolites (DAMs) and nine MEs were considerably affected in all organs. The concentration of all MEs varied significantly in at least one organ, while the K and Ca levels were markedly altered in all three. Most DAM levels increased in the stem but decreased in the root and leaf, implying that vulnerability segmentation may occur with long-term DS. The typical nitrogen- and carbon-compound levels similarly increased in the stem and decreased in the leaf and root, as the plant might respond to long-term DS by stabilizing respiration, promoting nitrogen recycling, and free radical scavenging. Correlation analysis showed several possible DAM-ME interactions and an association between Mn and flavonoids. Thus, survival strategies under long-term DS included sacrificing distal/vulnerable organs and accumulating function-specialized metabolites and MEs to mitigate drought-induced oxidative damage. This is the first study that reports substance fluctuations after long-term DS in different organs of plants, and highlights the need to use whole plants to fully comprehend stress response strategies.

Roles of metabolic regulation in developing Quercus variabilis acorns at contrasting geologically-derived phosphorus sites in subtropical China

BACKGROUND

Phosphorus (P) -rich soils develop in phosphorite residing areas while P-deficient soils are ubiquitous in subtropical regions. Little has been reported that how metabolites participate in the seed development and the processes involved in their coping with contrasting-nutrient environments.

RESULTS

Here we quantified the metabolites of Quercus variabilis acorns in the early (July), middle (August), late (September) development stages, and determined element (C, H, O, N, P, K, Ca, Mg, S, Fe, Al, Mn, Na, Zn, and Cu) concentrations of acorns in the late stage, at geologically-derived contrasting-P sites in subtropical China. The primary metabolic pathways included sugar metabolism, the TCA cycle, and amino acid metabolism. Most metabolites (especially C- and N-containing metabolites) increased and then decreased from July to September. Acorns between the two sites were significantly discriminated at the three stages, respectively, by metabolites (predominantly sugars and organic acids). Concentrations of P, orthophosphoric acid and most sugars were higher; erythrose was lower in late-stage acorns at P-rich sites than those at P-deficient sites. No significant differences existed in the size and dry mass of individual acorns between oak populations at the two sites.

CONCLUSIONS

Oak acorns at the two sites formed distinct metabolic phenotypes related to their distinct geologically-derived soil conditions, and the late-stage acorns tended to increase P-use-efficiency in the material synthesis process at P-deficient sites, relative to those at P-rich sites.

Applications of metabolomics in assessing ecological effects of emerging contaminants and pollutants on plants

Metabolomics, the global profiling of metabolite composition, is a powerful technique that can be applied to answer a diverse set of research questions concerning effects of toxicants on organisms. It has recently emerged as a tool to understand complex environmental perturbations in biological systems, especially at sub-lethal concentrations. Organisms can be affected by different stressors such as xenobiotics or increase in concentration of natural compounds such as nitrogen, phosphorous, and sulfur. Metabolomics has facilitated a better understanding of the effects of these perturbations on organisms such as plants, animals, and humans providing phenotypic and biological information in a high throughput manner. In this review, we will discuss recent applications of metabolomics to study the ecological effects of different environmental perturbations, including nanoparticles, pharmaceuticals and personal care products, pesticides, as well as the changes in natural compounds found in the environment with a focus on plant systems.

The Ionomics of Lettuce Infected by Xanthomonas campestris pv. vitians

Bacterial leaf spot (BLS) caused by Xanthomonas campestris pv. vitians (Xcv) places a major constraint on lettuce production worldwide. The most sustainable strategy known to date for controlling BLS is the use of resistant cultivars. The nutrient elemental signature (ionome) of ten lettuce cultivars with three levels of resistance was analyzed by inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine which nutrient balances are linked to resistance to BLS, and to assess the effect of Xcv infection on the ionome. The elemental concentrations were preprocessed with isometric log-ratios to define nutrient balances. Using this approach, 4 out of 11 univariate nutrient balances were found to significantly influence the resistance of lettuce cultivars to BLS (P < 0.05). These significant balances were the overall nutritional status balancing all measured nutrients with their complementary in the dry mass, as well as balances [Mn | Zn,Cu], [Zn | Cu], and [S,N | P]. Moreover, the infection of lettuce cultivars mostly affected the lettuce ionome on the [N,S | P] balance, where infection tended to lean the balance toward the N,S part relatively to P. This study shows that nutrient uptake in lettuce can be affected by BLS infection and that nutrient status influences resistance to BLS infection.

Nontargeted metabolomic analysis to unravel the impact of di (2-ethylhexyl) phthalate stress on root exudates of alfalfa (Medicago sativa)

Root exudates are the main media of information communication and energy transfer between plant roots and the soil. Understanding the response of root exudates to contamination stress is crucial in revealing the rhizoremediation mechanisms. Here, we investigate the response of alfalfa root exudates to bis(2-ethylhexyl) phthalate (DEHP) stress based on nontargeted metabolomic analysis. Alfalfa root exudates were collected using greenhouse hydroponic culture and analysed by gas chromatography-time of flight mass spectrometry (GC-TOFMS). A total of 314 compounds were identified in alfalfa root exudates of which carbohydrates, acids and lipids accounted for 28.6, 15.58 and 13.87%, respectively. Orthogonal partial least squares discriminant analysis (OPLS-DA) shows that DEHP exerted an important influence on the composition and quantity of root exudates. Fifty metabolites were clearly changed even at lower concentrations of DEHP, including common carbohydrates, fatty acids and some special rhizosphere signal materials, such as 4',5-dihyrroxy-7-methoxyisoflavone. DEHP stress significantly suppressed carbohydrate metabolism but promoted fatty acid metabolism. However, amino acid metabolism, lipid metabolism and the tricarboxylic acid (TCA) cycle showed little change in response to DEHP stress.