Glucose modulates copper induced changes in photosynthesis, ion uptake, antioxidants and proline in Cucumis sativus plants

The protective roles of boron against copper excess in citrus roots: Insights from physiology, transcriptome, and metabolome

Boron (B) deficiency and copper (Cu) excess are common problems in citrus orchard soils. Citrus sinensis seedlings were exposed to 25 (B25) or 2.5 (B2.5) μM H3BO3 and 0.5 (Cu0.5) or 350 (Cu350) μM CuCl3 for 24 weeks. Cu350 upregulated 2210 (1012) genes and 482 (341) metabolites and downregulated 3201 (695) genes and 175 (43) metabolites in roots at B2.5 (B25). Further analysis showed that the B-mediated mitigation of Cu toxicity in roots involved the coordination of the following aspects: (a) enhancing the ability to maintain cell wall and plasma membrane stability and function; (b) lowering the impairment of Cu350 to primary and secondary metabolisms and enhancing their adaptability to Cu350; and (c) alleviating Cu350-induced oxidative stress via the coordination of reactive oxygen species (ROS) and methylglyoxal detoxification systems. Cu350 upregulated the abundances of some saccharides, amino acids and derivatives, phospholipids, secondary metabolites, and vitamins, and the expression of several ROS detoxification-related genes in roots of B2.5-treated seedlings (RB2.5), but these adaptive responses did not prevent RB2.5 from Cu-toxicity (oxidative damage). The study identified some genes, metabolites, and metabolic processes/pathways possibly involved in root Cu tolerance. Additionally, the responses of gene expression and metabolite profiling to Cu-B treatments differed between leaves and roots. Therefore, this study provided novel information for B to reduce Cu toxicity in roots and might contribute to the development of soil amendments targeting Cu excess in citrus and other crops.

Sugar-coating on the surface of silica nanoparticles attenuates the dose- and size-dependent toxicity of the nanoparticles for plant-based applications

Silica nanoparticles (SiNPs) are one of the most promising nanoparticles in stimulating plant growth and alleviating environmental stresses. Besides beneficial attributes, these nanoparticles may also possess serious toxicity issues. In this context, the present study aimed to evaluate the dose and size-dependent toxicity attributes of SiNPs using Allium cepa root tip assay. The dose-dependent study conducted using moderate-size SiNPs (∼50 nm) with different concentrations (1-500 g/L) depicted non-toxic effects up to the dose of 75 g/L. However, concentrations above 100 g/L imparted a gradual increase in toxicity with the increasing dosage of SiNPs, where mitotic index (MI) was reduced, and chromosomal aberration (CA), ROS accumulation, and membrane disruption increased significantly. Moreover, among the 3 different sizes of SiNPs viz. ∼30, ∼50, and ∼100 nm, ∼50 nm was relatively non-toxic. Further, a significant reduction in toxicity level at higher concentrations (≥200 g/L) was achieved when the SiNPs (∼50 nm) surface was functionalized with glucose (GSiNPs) and trehalose (TSiNPs) compared to bare SiNPs. In this context, the reduction in CA by GSiNPs was 1.6-2.9 folds and by TSiNPs 1.9-3.3 folds. Also, GSiNPs and TSiNPs improved the plant growth and soil microflora colonization, without imparting toxic effects.

Mitigation of cadmium stress by salicylic acid: Physiological and biochemical responses in NM-2006, NM-92, and Mash-88 mung bean varieties

Cadmium (Cd) is a major environmental pollutant that adversely affects plant growth and productivity, creating a need for effective mitigation strategies. This study aims to evaluate the impact of salicylic acid (SA) priming on the physio-biochemical characteristics of three mung bean varieties (Vigna radiata L.), namely NM-2006, NM-92, and Mash-88, under Cd stress. To achieve this, the mung bean varieties were subjected to Cd stress with and without SA priming, and their growth, chlorophyll content, protein levels, and oxidative stress markers were analyzed. Results showed significant reductions in growth, chlorophyll, and protein contents, alongside increased oxidative stress markers such as hydrogen peroxide and malondialdehyde under Cd stress. Moreover, Cd exposure also led to higher levels of proline, glycine betaine, and total soluble sugars. However, SA priming alleviated these adverse effects by enhancing growth, chlorophyll fluorescence, and protein content while reducing oxidative damage by upregulating the enzymatic antioxidant mechanism. Additionally, SA priming also modulated phytohormone levels, specifically increasing abscisic acid and jasmonic acid while decreasing ethylene. Comparative analysis revealed that NM-2006 suffered the most from Cd stress, NM-92 showed a better response to SA priming, and Mash-88 exhibited the least damage and greatest benefit from SA priming. These findings suggest that SA is an effective protective agent that enhances stress tolerance in mung bean varieties, offering valuable insights for improving crop resilience in contaminated environments.

Mechanisms by Which Increased pH Ameliorates Copper Excess in Citrus sinensis Roots: Insight from a Combined Analysis of Physiology, Transcriptome, and Metabolome

Limited data are available on copper (Cu)-pH interaction-responsive genes and/or metabolites in plant roots. Citrus sinensis seedlings were treated with 300 μM (Cu toxicity) or 0.5 μM (control) CuCl2 at pH 3.0 or 4.8 for 17 weeks. Thereafter, gene expression and metabolite profiles were obtained using RNA-Seq and widely targeted metabolome, respectively. Additionally, several related physiological parameters were measured in roots. The results indicated that elevating the pH decreased the toxic effects of Cu on the abundances of secondary metabolites and primary metabolites in roots. This difference was related to the following several factors: (a) elevating the pH increased the capacity of Cu-toxic roots to maintain Cu homeostasis by reducing Cu uptake and Cu translocation to young leaves; (b) elevating the pH alleviated Cu toxicity-triggered oxidative damage by decreasing reactive oxygen species (ROS) formation and free fatty acid abundances and increasing the ability to detoxify ROS and maintain cell redox homeostasis in roots; and (c) increasing the pH prevented root senescence and cell wall (CW) metabolism impairments caused by Cu toxicity by lowering Cu levels in roots and root CWs, thus improving root growth. There were some differences and similarities in Cu-pH interaction-responsive genes and metabolites between leaves and roots.

Investigating the influence of selenium and epibrassinolide on antioxidant activity, proline accumulation, and protein expression profiles in wheat plants experiencing heat and drought stress

In the current investigation, the combination of selenium (Se) and epibrassinolide (EBL) exhibited a promising alleviative response against the concurrent stress of heat and drought in wheat plants. The compromised growth and photosynthetic performance of wheat plants under the combined stress of heat and drought were substantially improved with the treatment involving Se and EBL. This improvement was facilitated through the expression of Q9FIE3 and O04939 proteins, along with enhanced antioxidant activities. The heightened levels of antioxidant enzymes and the accumulation of osmoprotectant proline helped mitigate the overaccumulation of reactive oxygen species (ROS), including electrolyte leakage, H2O2 accumulation, and lipid peroxidation, thus conferring tolerance against the combined stress of heat and drought. Studies have demonstrated that Se and EBL can assist wheat plants in recuperating from the adverse effects of heat and drought. As such, they are essential components of sustainable farming methods that aim to increase crop productivity.

The underlying mechanisms by which boron mitigates copper toxicity in Citrus sinensis leaves revealed by integrated analysis of transcriptome, metabolome and physiology

Both copper (Cu) excess and boron (B) deficiency are often observed in some citrus orchard soils. The molecular mechanisms by which B alleviates excessive Cu in citrus are poorly understood. Seedlings of sweet orange (Citrus sinensis (L.) Osbeck cv. Xuegan) were treated with 0.5 (Cu0.5) or 350 (Cu350 or Cu excess) μM CuCl2 and 2.5 (B2.5) or 25 (B25) μM HBO3 for 24 wk. Thereafter, this study examined the effects of Cu and B treatments on gene expression levels revealed by RNA-Seq, metabolite profiles revealed by a widely targeted metabolome, and related physiological parameters in leaves. Cu350 upregulated 564 genes and 170 metabolites, and downregulated 598 genes and 58 metabolites in leaves of 2.5 μM B-treated seedlings (LB2.5), but it only upregulated 281 genes and 100 metabolites, and downregulated 136 genes and 40 metabolites in leaves of 25 μM B-treated seedlings (LB25). Cu350 decreased the concentrations of sucrose and total soluble sugars and increased the concentrations of starch, glucose, fructose and total nonstructural carbohydrates in LB2.5, but it only increased the glucose concentration in LB25. Further analysis demonstrated that B addition reduced the oxidative damage and alterations in primary and secondary metabolisms caused by Cu350, and alleviated the impairment of Cu350 to photosynthesis and cell wall metabolism, thus improving leaf growth. LB2.5 exhibited some adaptive responses to Cu350 to meet the increasing need for the dissipation of excessive excitation energy (EEE) and the detoxification of reactive oxygen species (reactive aldehydes) and Cu. Cu350 increased photorespiration, xanthophyll cycle-dependent thermal dissipation, nonstructural carbohydrate accumulation, and secondary metabolite biosynthesis and abundances; and upregulated tryptophan metabolism and related metabolite abundances, some antioxidant-related gene expression, and some antioxidant abundances. Additionally, this study identified some metabolic pathways, metabolites and genes that might lead to Cu tolerance in leaves.

Metabolite responses of cucumber on copper toxicity in presence of fullerene C60 derivatives

Copper (Cu) toxicity in crops is a result of excessive release of Cu into environment. Little is known about mitigation of Cu toxicity through the application of carbon-based nanomaterials including water-soluble fullerene C60 derivatives. Two derivatives of fullerene were examined: polyhydroxylated C60 (fullerenol) and arginine C60 derivative. In order to study the response of Cu-stressed plants (Cucumis sativus L.) to these nanomaterials, metabolomics analysis by gas chromatography-mass spectrometry (GC-MS) was performed. Excess Cu (15 μM) caused substantial increase in xylem sap Cu, retarded dry biomass and leaf chlorosis of hydroponically grown cucumber. In Cu-stressed leaves, metabolomes was disturbed towards suppression metabolism of nitrogen (N) compounds and activation metabolism of hexoses. Also, upregulation of some metabolites involving in antioxidant defense system, such as ascorbic acid, tocopherol and ferulic acid, was occurred in Cu-stressed leaves. Hydroponically added fullerene adducts decreased the xylem sap Cu and alleviated Cu toxicity with effectiveness has been most pronounced for arginine C60 derivative. Metabolic responses of plants subjected to high Cu with fullerene derivatives were opposite to that observed under Cu alone. Fatty acids up-regulation (linolenic acid) and antioxidant molecules (tocopherol) down-regulation might indicate that arginine C60 adduct can alleviate Cu induced oxidative stress. Although fullerenol slightly improved cucumber growth, its effect on metabolic state of Cu-stressed plants was not statistically significant. We suggest that tested fullerene C60 adducts have a potential to prevent Cu toxicity in plants through a mechanism associated with their capability to restrict xylem transport of Cu from roots to shoot, and to maintain antioxidative properties of plants.

Metabolomics combined with physiology and transcriptomics reveal key metabolic pathway responses in apple plants exposure to different selenium concentrations

Selenium (Se) can be absorbed by plants, thereby affects plant physiological activity, interferes gene expression, alters metabolite content and influences plant growth. However, the molecular mechanism underlying the plant response to Se remains unclear. In this study, apple plants were exposed to Se at concentrations of 0, 3, 6, 9, 12, 24, and 48 μM. Low concentrations of Se promoted plant growth, while high Se concentrations (≥24 μM) reduced photosynthesis, disturbed carbon and nitrogen metabolism, damaged the antioxidant system, and ultimately inhibited plant growth. The transcriptome and metabolome revealed that Se mainly affected three pathways, namely the 'biosynthesis of amino acids', 'starch and sucrose metabolism', and 'phenylpropanoid biosynthesis' pathways. 9 μM Se improved the synthesis, catabolism and utilization of amino acids and sugars, ultimately promoted plant growth. However, 24 μM Se up-regulated the related genes expression of PK, GPT, P5CS, SUS, SPS and CYP98A, and accumulated a large number of osmoregulation substances, such as citric acid, L-proline, D-sucrose and chlorogenic acid in the roots, ultimately affected the balance between plant growth and defense. In conclusion, this study reveals new insights into the key metabolic pathway in apple plants responses to Se.

Citrus sinensis manganese tolerance: Insight from manganese-stimulated secretion of root exudates and rhizosphere alkalization

We used manganese (Mn)-tolerant 'Xuegan' (Citrus sinensis) seedlings as materials and examined the characterization of Mn uptake and Mn-activated-release of root exudates under hydroponic conditions. We observed that root and shoot Mn bioaccumulation factor (BCF) reduced with the increase of Mn supply, and that Mn transfer factor (Tf) reduced greatly as Mn supply increased from 0 to 500 μM, beyond which Tf slightly increased with increasing Mn supply, suggesting that Mn supply reduced the ability to absorb and accumulate Mn in roots and shoots, as well as root-to-shoot Mn translocation. Without Mn, roots alkalized the solution pH from 5.0 to above 6.2, while Mn supply reduced root-induced alkalization. As Mn supply increased from 0 to 2000 μM, the secretion of root total phenolics (TPs) increased, while the solution pH decreased. Mn supply did not alter the secretion of root total free amino acids, total soluble sugars, malate, and citrate. Mn-activated-release of TPs was inhibited by low temperature and anion channel inhibitors, but not by protein biosynthesis inhibitor. Using widely targeted metabolome, we detected 48 upregulated [35 upregulated phenolic compounds + 13 other secondary metabolites (SMs)] and three downregulated SMs, and 39 upregulated and eight downregulated primary metabolites (PMs). These findings suggested that reduced ability to absorb and accumulate Mn in roots and shoots and less root-to-shoot Mn translocation in Mn-toxic seedlings, rhizosphere alkalization, and Mn-activated-release of root exudates (especially phenolic compounds) contributed to the high Mn tolerance of C. sinensis seedlings.

Unveiling plant defense arsenal: metabolic strategies in Brassica oleracea during black rot disease

Alterations in plant metabolism play a key role in the complex plant-pathogen interactions. However, there is still a lack of knowledge about the connection between changes in primary and specialized metabolism and the plant defense against diseases that impact crops. Thus, we aim to study the metabolic reprograming in Brassica oleracea plants upon infection by Xanthomonas campestris pv. campestris (Xcc). To accomplish this, we utilized a combination of untargeted and targeted metabolomics, through UPLC-Q-TOF-MS/MS and 1H-NMR, in two crop lines differing in resistance that were evaluated at two- and four-week intervals following inoculation (T1 and T2, respectively). Besides, to depict the physiological status of the plant during infection, enzymatic activities related to the carbohydrate pathway and oxidative stress were studied. Our results revealed different temporal dynamics in the responses of the susceptible vs. resistant crops lines. Resistant B. oleracea line suppresses carbohydrate metabolism contributing to limit nutrient supplies to the bacterium and prioritizes the induction of defensive compounds such as indolic glucosinolates, salicylic acid, phenylpropanoids and phytoalexins precursors at early infection stages. In contrast, the susceptible line invests in carbohydrate metabolism, including enzymatic activities related to the hexoses turnover, and activates defense signaling related to reactive oxygen species. Thus, each line triggers a different metabolic strategy that will affect how the plant overcomes the disease in terms of resistance and growth. This work provides first insights of a fine-tuned metabolic regulation during Xcc infection in B. oleracea that will contribute to develop new strategies for plant disease management.

Regulation on copper-tolerance in Citrus sinensis seedlings by boron addition: Insights from root exudates, related metabolism, and gene expression

Boron (B) can alleviate Citrus copper (Cu)-toxicity. However, the underlying mechanism by which B mitigates Cu-toxicity is unclear. 'Xuegan' (Citrus sinensis) seedlings were exposed to 0.5 (control) or 350 (Cu-toxicity) µM Cu and 2.5 or 25 µM B for 24 weeks. Thereafter, we investigated the secretion of low molecular weight compounds [LMWCs; citrate, malate, total soluble sugars (TSS), total phenolics (TP), and total free amino acids (TFAA)] by excised roots and their concentrations in roots and leaves, as well as related enzyme gene expression and activities in roots and leaves. Cu-stress stimulated root release of malate and TFAA, which might contribute to citrus Cu-tolerance. However, B-mediated-mitigation of Cu-stress could not be explained in this way, since B addition failed to further stimulate malate and TFAA secretion. Indeed, B addition decreased Cu-stimulated-secretion of malate. Further analysis suggested that Cu-induced-exudation of malate and TFAA was not regulated by their levels in roots. By contrast, B addition increased malate, citrate, and TFAA concentrations in Cu-toxic roots. Cu-toxicity increased TP concentration in 25 μM B-treated leaves, but not in 2.5 μM B-treated leaves. Our findings suggested that the internal detoxification of Cu by LMWCs played a role in B-mediated-alleviation of Cu-toxicity.

Exogenous application of stevioside enhances root growth promotion in soybean (Glycine max (L.) Merrill)

The present study aims to investigate the impact of externally applied stevioside (a sugar-based glycoside) on soybean root growth by examining morpho-physiological characteristics, biochemical parameters, and gene expression. Soybean seedlings (10-day-old) were treated with stevioside (0, 8.0 μM, 24.5 μM, and 40.5 μM) for four times at six days' intervals by soil drenching. Treatment with 24.5 μM stevioside significantly increased root length (29.18 cm plant-1), root numbers (38.5 plant-1), root biomass (0.95 g plant-1 FW; 0.18 g plant-1 DW), shoot length (30.96 cm plant-1), and shoot biomass (2.14 g plant-1 FW; 0.36 g plant-1 DW) compared to the control. Moreover, 24.5 μM of stevioside was effective in enhancing photosynthetic pigments, leaf relative water content, and antioxidant enzymes compared to control. Conversely, plants exposed to a higher concentration of stevioside (40.5 μM), elevated total polyphenolic content, total flavonoid content, DPPH activity, total soluble sugars, reducing sugars, and proline content. Furthermore, gene expression of root growth development-related genes such as GmYUC2a, GmAUX2, GmPIN1A, GmABI5, GmPIF, GmSLR1, and GmLBD14 in stevioside-treated soybean plants were evaluated. Stevioside (8.0 μM) showed significant expression of GmPIN1A, whereas, 40.5 μM of stevioside enhanced GmABI5 expression. In contrast, most of the root growth development genes such as GmYUC2a, GmAUX2, GmPIF, GmSLR1, and GmLBD14, were highly expressed at 24.5 μM of stevioside treatment. Taken together, our results demonstrate the potential of stevioside in improving morpho-physiological traits, biochemical status, and the expression of root development genes in soybean. Hence, stevioside could be used as a supplement to enhance plant performance.

Modification of Sugar Profile and Ripening in Atemoya (Annona × atemoya Mabb.) Fruits through Copper Hydroxide Application

Atemoya (Annona × atemoya Mabb.), a climacteric fruit of the Annonaceae family, is becoming increasingly popular due to its organoleptic and nutritional properties. Anthracnose, a fungus of the Colletotrichum genus, is one of the most serious diseases in orchards, causing significant damage if not controlled, so producers use phytosanitary products. The current study sought to investigate the quality of atemoya fruits after harvest in an orchard with anthracnose controlled by Cu(OH)² application: T1-no Cu(OH)², T2-7.8 mL Cu(OH)² L1 divided into two applications, T3-15.6 mL Cu(OH)² L1 divided into four, T4-8.0 mL Cu(OH)² L1 divided into eight, and T5-13.0 mL Cu(OH)² L1 divided into thirteen applications. The sugar profile of fruits was examined, as well as MDA, H₂O₂, and quality parameters such as pH, mass, soluble solids, titratable acidity, and maturation index. MDA, such as H₂O₂, can function as a signal molecule. Eight applications of 1.0 mL L-1 Cu(OH)² resulted in increased concentrations of H₂O₂ and MDA, signal molecules involved in sugar modification profiles such as glucose, fructose, and trehalose. It also had a high titratable acidity, a lower maturation index, better fruit quality, and a longer shelf life.

Could nitrogen compounds be indicators of tolerance to high doses of Cu and Fe in the cultivation of Leucaena leucocephala?

Nitrogen metabolism and the production of primary and secondary metabolites vary according to biotic and abiotic factors such as trace elements (TE) stress, and can, therefore, be considered biomarkers. The present study evaluated the effect of copper (Cu) and iron (Fe) TE, separately, on the metabolism of nitrogen compounds and biomass production, partitioned into shoot and roots of Leucaena leucocephala (Lam.) de Wit., and identified possible defense mechanisms linked to nitrogen metabolism. At 120 days of cultivation, the biomass production of L. leucocephala was higher when exposed to excess Fe than Cu. Nonetheless, the biomass gain (%) of plants exposed to Cu was higher, especially the biomass gains in roots. The tolerance and biomass production of L. leucocephala is related to the regulation of nitrogen metabolism and production of secondary metabolites. The biochemistry of plant metabolism against the excess of Cu and Fe TE manifested similarly, but with some specifics regarding the chemical nature of each metal. There was a reduction in the content of ureides and proteins and an increase in amino acids in the roots in relation to the increase in Cu and Fe concentrations. There was low accumulation of proline in the roots in treatments 400 and 500 mg/dm³ compared to the control for both TE. On the other hand, the total phenolic compounds in the roots increased. Our results indicate that the increased synthesis of amino acids and the accumulation of phenolic compounds is involved in the tolerance of L. leucocephala to Cu and Fe.

Physiological and biochemical bases of spermidine-induced alleviation of cadmium and lead combined stress in rice

Cadmium (Cd) and lead (Pb) pollution is a major environmental issue affecting plant production. Spermidine (Spd) is involved in plant response to abiotic stress. However, the role and associated mechanism of Spd under Cd + Pb combined stress are poorly understood. The potential protective role of Spd at different concentration on rice (Oryza sativa L.) seedlings exposed to Cd + Pb treatment was investigated by a hydroponic experiment in this study. The results showed that exogenous Spd enhanced the tolerance of rice seedlings to Cd + Pb stress, resulted in an increase in plant height, root length, fresh weight and dry weight of roots and shoots. Further, application of Spd decreased the contents of hydrogen peroxide, superoxide anion, malondialdehyde, and the accumulation of Cd and Pb, and increased the contents of mineral nutrient, carotenoids, chlorophyll, proline, soluble sugar, soluble protein, total phenol, flavonoid, anthocyanin, and antioxidant enzymes activities in roots and shoots of rice seedlings under Cd + Pb stress. Particularly, 0.5 mmol L^-1 Spd was the most effective to alleviate the adverse impacts on growth and physiological metabolism of rice seedlings under Cd + Pb stress. Principal component analysis and heat map clustering established correlations between physio-biochemical parameters and further revealed Spd alleviated Cd + Pb damage in rice seedling was associated with inhibition of accumulation and translocation of Cd and Pb, increasing the contents of photosynthetic pigments and mineral nutrient and stimulation of antioxidative response and osmotic adjustment. Overall, our findings provide an important prospect for use of Spd in modulating Cd + Pb tolerance in rice plants. Spd could help to alleviate Cd + Pb damage through inhibition of accumulation and translocation of Cd and Pb and stimulation of oxidant-defense system and osmotic adjustment.

Effects of copper and arsenic on their uptake and distribution in As-hyperaccumulator Pteris vittata

Arsenic (As) and copper (Cu) are common co-contaminates in soils. However, their interactive effects on their accumulation and distribution in As-hyperaccumulator Pteris vittata are poorly understood. A hydroponic experiment was conducted with As being 0, 5, or 50 μM and Cu being 0.32, 3.2, or 32 μM to evaluate their phytotoxicity, accumulation, and distribution in P. vittata. In addition, As and Cu uptake kinetics were examined using the Michaelis-Menten kinetics model. Total As and Cu concentrations in P. vittata were up to 487 and 1355 mg kg^-1. About 39-81% of the As was in the fronds compared to 0.6-18% for Cu. At 50 μM As, increasing Cu concentration from 0.32 to 32 μM increased root As while decreasing frond As concentrations, with the translocation factor (ratio of As in fronds to roots) being reduced from 4.0 to 0.31. In contrast, As did not affect Cu accumulation in P. vittata. Michaelis constant K_m value for As was higher than that of Cu (6.49-24.9 vs. 0.43-3.36), consistent with higher Cu uptake than As. Besides, Cu reduced root K but increased P levels in the roots, whereas As increased the K and P concentrations in the fronds. Our results suggest that P. vittata accumulated more Cu than As in the roots, contributing to its low As translocation. As such, high levels of Cu are likely to reduce As uptake by P. vittata during phytoremediation of As-contaminated sites.

Effects of Plant Hormones, Metal Ions, Salinity, Sugar, and Chemicals Pollution on Glucosinolate Biosynthesis in Cruciferous Plant

Cruciferous vegetable crops are grown widely around the world, which supply a multitude of health-related micronutrients, phytochemicals, and antioxidant compounds. Glucosinolates (GSLs) are specialized metabolites found widely in cruciferous vegetables, which are not only related to flavor formation but also have anti-cancer, disease-resistance, and insect-resistance properties. The content and components of GSLs in the Cruciferae are not only related to genotypes and environmental factors but also are influenced by hormones, plant growth regulators, and mineral elements. This review discusses the effects of different exogenous substances on the GSL content and composition, and analyzes the molecular mechanism by which these substances regulate the biosynthesis of GSLs. Based on the current research status, future research directions are also proposed.

Oxidative RNA Modifications as an Early Response of Soybean (Glycine max L.) Exposed to Copper and Lead

Plant exposure to metals is associated with the accumulation of reactive oxygen species, which mediate the oxidation of various molecules including lipids, proteins, and nucleic acids. The aim of the present study is the evaluation of the impact of short-term Cu and Pb treatment on oxidative events in the roots of soybean seedlings, with special emphasis on RNA oxidation. The results show that an increase in total RNA oxidative modification, 8-hydroxyguanosine (8-OHG), constitutes a very early response to both applied metals, observed already within the first hour of treatment. Exposure to Cu and Pb resulted also in the increase in superoxide anion and hydrogen peroxide levels and intensified lipid peroxidation. However, these responses were most prominent after longer treatment times. On the other hand, no changes were observed in the level of protein carbonylation. It can be concluded that 8-OHG enrichment in total RNA constitutes one of the earliest reactions to metals, which precedes the symptoms of oxidative stress.

Metabolomics combined with physiology and transcriptomics reveals how Citrus grandis leaves cope with copper-toxicity

Limited data are available on metabolic responses of plants to copper (Cu)-toxicity. Firstly, we investigated Cu-toxic effects on metabolomics, the levels of free amino acids, NH₄⁺-N, NO₃^--N, total nitrogen, total soluble proteins, total phenolics, lignin, reduced glutathione (GSH) and malondialdehyde, and the activities of nitrogen-assimilatory enzymes in 'Shatian' pummelo (Citrus grandis) leaves. Then, a conjoint analysis of metabolomics, physiology and transcriptomics was performed. Herein, 59 upregulated [30 primary metabolites (PMs) and 29 secondary metabolites (SMs)] and 52 downregulated (31 PMs and 21 SMs) metabolites were identified in Cu-toxic leaves. The toxicity of Cu to leaves was related to the Cu-induced accumulation of NH₄⁺ and decrease of nitrogen assimilation. Metabolomics combined with physiology and transcriptomics revealed some adaptive responses of C. grandis leaves to Cu-toxicity, including (a) enhancing tryptophan metabolism and the levels of some amino acids and derivatives (tryptophan, phenylalanine, 5-hydroxy-l-tryptophan, 5-oxoproline and GSH); (b) increasing the accumulation of carbohydrates and alcohols and upregulating tricarboxylic acid cycle and the levels of some organic acids and derivatives (chlorogenic acid, quinic acid, d-tartaric acid and gallic acid o-hexoside); (c) reducing phospholipid (lysophosphatidylcholine and lysophosphatidylethanolamine) levels, increasing non-phosphate containing lipid [monoacylglycerol ester (acyl 18:2) isomer 1] levels, and inducing low-phosphate-responsive gene expression; and (d) triggering the biosynthesis of some chelators (total phenolics, lignin, l-trytamine, indole, eriodictyol C-hexoside, quercetin 5-O-malonylhexosyl-hexoside, N-caffeoyl agmatine, N'-p-coumaroyl agmatine, hydroxy-methoxycinnamate and protocatechuic acid o-glucoside) and vitamins and derivatives (nicotinic acid-hexoside, B₁ and methyl nicotinate). Cu-induced upregulation of many antioxidants could not protect Cu-toxic leaves from oxidative damage. To conclude, our findings corroborated the hypothesis that extensive reprogramming of metabolites was carried out in Cu-toxic C. grandis leaves in order to cope with Cu-toxicity.