Cerium relieves the inhibition of nitrogen metabolism of spinach caused by magnesium deficiency

New insights into comprehensive analysis of magnesium transporter (MGT) gene family in rice (Oryza sativa L.)

Magnesium transporters (MGTs) regulate magnesium absorption, transport, and redistribution in higher plants. To investigate the role of the Oryza sativa MGTs gene family members under salt stress, this study analyzed the protein properties, gene structure, phylogenetic relationship, synteny patterns, expression, and co-expression networks of 23 non-redundant OsMGT. The evolutionary relationship of the OsMGT gene family was fully consistent with their functional domain, and were divided into three main classes based on the conserved domain: MMgT, CorA-like, and NIPA. The α/β patterns in the protein structures were highly similar in the CorA-like and NIPA members, with the conserved structures in the Mg2+-binding and catalytic regions. The CorA-like clade-related proteins demonstrated the highest numbers of protein channels with Pro, Ser, Lys, Gly, and Tyr, as the critical binding residues. The expression analysis of OsMGT genes in various tissues showed that MGTs' gene family may possess critical functions during rice development. Gene expression analysis of candidate OsMGT using reverse-transcription quantitative real-time PCR (RT-qPCR) found that four OsMGT genes exhibited different expression patterns in salt-sensitive and salt-tolerant rice genotypes. We hypothesize that the OsMGT gene family members may be involved in responses to salt stress. These findings could be useful for further functional investigation of MGTs as well as defining their involvement in abiotic stress studies.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03735-4.

Response of Medical Cannabis to Magnesium (Mg) Supply at the Vegetative Growth Phase

Recent studies demonstrated a significant impact of some major macronutrients on function and production of medical cannabis plants, yet information on the effect of most nutrients, including Mg, is scarce. Magnesium is required for major physiological functions and metabolic processes in plants, and in the present study we studied the effects of five Mg treatments (2, 20, 35, 70, and 140 mg L^-1 Mg), on plant development and function, and distribution of minerals in drug-type (medical) cannabis plants, at the vegetative growth phase. The plants were cultivated in pots under controlled environment conditions. The results demonstrate that plant development is optimal under Mg supply of 35-70 mg L^-1 (ppm), and impaired under lower Mg input of 2-20 mg L^-1. Two mg L^-1 Mg resulted in visual deficiency symptoms, shorter plants, reduced photosynthesis rate, transpiration rate, photosynthetic pigments and stomatal conduction in young-mature leaves, and a 28% reduction of total plant biomass compared to the optimal supply of 35 mg L^-1 Mg. The highest supply level of 140 mg L^-1 Mg induced a small decrease in physiological function, which did not affect morphological development and biomass accumulation. The low-deficient Mg supply of 2 mg L^-1 Mg stimulated Mg uptake and accumulation of N, P, K, Ca, Mn, and Zn in the plant. Increased Mg supply impaired uptake of Ca and K and their root-to-shoot translocation, demonstrating competitive cation inhibition. Mg-deficiency symptoms developed first in old leaves (at 2 mg L^-1 Mg) and progressed towards young-mature leaves, demonstrating ability for Mg in-planta storage and remobilization. Mg toxicity symptoms appeared in old leaves from the bottom of the plants, under 140 mg L^-1 Mg. Taken together, the findings suggest 35-70 mg L^-1 Mg as the optimal concentration range for cannabis plant development and function at the vegetative growth phase.

Magnesium Nutrient Application Induces Metabolomics and Physiological Responses in Mulberry (Morus alba) Plants

Mulberry (Morus alba) is a significant plant with numerous economic benefits; however, its growth and development are affected by nutrient levels. A high level of magnesium (Mg) or magnesium nutrient starvation are two of the significant Mg factors affecting plant growth and development. Nevertheless, M. alba's metabolic response to different Mg concentrations is unclear. In this study, different Mg concentrations, optimal (3 mmol/L), high (6 mmol/L and 9 mmol/L), or low (1 and 2 mmol/L) and deficient (0 mmol/L), were applied to M. alba for three weeks to evaluate their effects via physiological and metabolomics (untargeted; liquid chromatography-mass spectrometry (LC-MS)) studies. Several measured physiological traits revealed that Mg deficiency and excess Mg altered net photosynthesis, chlorophyll content, leaf Mg content and fresh weight, leading to remarkable reductions in the photosynthetic efficiency and biomass of mulberry plants. Our study reveals that an adequate supply of the nutrient Mg promoted the mulberry's physiological response parameters (net photosynthesis, chlorophyll content, leaf and root Mg content and biomass). The metabolomics data show that different Mg concentrations affect several differential metabolite expressions (DEMs), particularly fatty acyls, flavonoids, amino acids, organic acid, organooxygen compounds, prenol lipids, coumarins, steroids and steroid derivatives, cinnamic acids and derivatives. An excessive supply of Mg produced more DEMs, but negatively affected biomass production compared to low and optimum supplies of Mg. The significant DEMs correlated positively with mulberry's net photosynthesis, chlorophyll content, leaf Mg content and fresh weight. The mulberry plant's response to the application of Mg used metabolites, mainly amino acids, organic acids, fatty acyls, flavonoids and prenol lipids, in the KEGG (Kyoto Encyclopedia of Genes and Genomes) pathways. These classes of compounds were mainly involved in lipid metabolism, amino acid metabolism, energy metabolism, the biosynthesis of other secondary metabolites, the biosynthesis of other amino acids, the metabolism of cofactors and vitamin pathways, indicating that mulberry plants respond to Mg concentrations by producing a divergent metabolism. The supply of Mg nutrition was an important factor influencing the induction of DEMs, and these metabolites were critical in several metabolic pathways related to magnesium nutrition. This study provides a fundamental understanding of DEMs in M. alba's response to Mg nutrition and the metabolic mechanisms involved, which may be critical to the mulberry genetic breeding program.

Magnesium promotes tea plant growth via enhanced glutamine synthetase-mediated nitrogen assimilation

Acidic tea (Camellia sinensis) plantation soil usually suffers from magnesium (Mg) deficiency, and as such, application of fertilizer containing Mg can substantially increase tea quality by enhancing the accumulation of nitrogen (N)-containing chemicals such as amino acids in young tea shoots. However, the molecular mechanisms underlying the promoting effects of Mg on N assimilation in tea plants remain unclear. Here, both hydroponic and field experiments were conducted to analyze N, Mg, metabolite contents, and gene expression patterns in tea plants. We found that N and amino acids accumulated in tea plant roots under Mg deficiency, while metabolism of N was enhanced by Mg supplementation, especially under a low N fertilizer regime. 15N tracing experiments demonstrated that assimilation of N was induced in tea roots following Mg application. Furthermore, weighted gene correlation network analysis (WGCNA) analysis of RNA-seq data suggested that genes encoding glutamine synthetase isozymes (CsGSs), key enzymes regulating N assimilation, were markedly regulated by Mg treatment. Overexpression of CsGS1.1 in Arabidopsis (Arabidopsis thaliana) resulted in a more tolerant phenotype under Mg deficiency and increased N assimilation. These results validate our suggestion that Mg transcriptionally regulates CsGS1.1 during the enhanced assimilation of N in tea plant. Moreover, results of a field experiment demonstrated that high Mg and low N had positive effects on tea quality. This study deepens our understanding of the molecular mechanisms underlying the interactive effects of Mg and N in tea plants while also providing both genetic and agronomic tools for future improvement of tea production.

Divergent effects of cerium oxide nanoparticles alone and in combination with cadmium on nutrient acquisition and the growth of maize (Zea mays)

INTRODUCTION

The increasing use of cerium nanoparticles (CeO₂-NPs) has made their influx in agroecosystems imminent through air and soil deposition or untreated wastewater irrigation. Another major pollutant associated with anthropogenic activities is Cd, which has adverse effects on plants, animals, and humans. The major source of the influx of Cd and Ce metals in the human food chain is contaminated food, making it an alarming issue; thus, there is a need to understand the factors that can reduce the potential damage of these heavy metals.

METHODS

The present investigation was conducted to evaluate the effect of CeO₂-10-nm-NPs and Cd (alone and in combination) on Zea mays growth. A pot experiment (in sand) was conducted to check the effect of 0, 200, 400, 600, 1,000, and 2,000 mg of CeO₂-10 nm-NPs/kg^-1 dry sand alone and in combination with 0 and 0.5 mg Cd/kg^-1 dry sand on maize seedlings grown in a partially controlled greenhouse environment, making a total of 12 treatments applied in four replicates under a factorial design. Maize seedling biomass, shoot and root growth, nutrient content, and root anatomy were measured.

RESULTS AND DISCUSSION

The NPs were toxic to plant biomass (shoot and root dry weight), and growth at 2,000 ppm was the most toxic in Cd-0 sets. For Cd-0.5 sets, NPs applied at 1,000 ppm somewhat reverted Cd toxicity compared with the contaminated control (CC). Additionally, CeO₂-NPs affected Cd translocation, and variable Ce uptake was observed in the presence of Cd compared with non-Cd applied sets. Furthermore, CeO₂-NPs partially controlled the elemental content of roots and shoots (micronutrients such as B, Mn, Ni, Cu, Zn, Mo, and Fe and the elements Co and Si) and affected root anatomy.

Transcriptome analysis reveals MYB and WRKY transcription factors involved in banana (Musa paradisiaca AA) magnesium deficiency

The banana development was inhibited under the long-term magnesium deficiency (MD) stress, resulting in the leaf chlorosis. MYB108 and WRKY75 are involved in regulating the growth and development of banana leaves and roots under long-term MD. Magnesium deficiency (MD) causes plant growth inhibition, ageing acceleration, yield reduction and quality decline of banana (Musa paradisiaca AA), but the molecular regulatory mechanisms underlying the changes in response to long-term MD conditions remain unknown. In this study, a long-term MD experiment was performed with banana seedlings at the four-leaf stage. Compared to those in the control group, the growth of leaves and roots of seedlings in the long-term MD treatment experimental groups was inhibited, and the Mg content and chlorophyll contents were decreased. Leaves and roots of seedlings from the control and experimental groups were subsequently collected for RNA sequencing to identify the genes that respond to long-term MD. More than 50 million reads were identified from each sample, resulting in the detection of 3500 and 948 differentially expressed genes (DEGs) in the leaves and roots, respectively. MYB and WRKY transcription factors (TFs) involved in plant stress responses were selected for further analysis, and 102 MYB and 149 WRKY TFs were differentially expressed. Furthermore, two highly differentially expressed candidate genes, MYB108 and WRKY75, were functionally analyzed using Arabidopsis mutants grown under long-term MD conditions. The results showed that the density of root hairs on the wild type (WT) was than that on the myb108 and wrky75 mutants under MD, implying that the mutants were more sensitive to MD than the WT. This research broadens our understanding the underlying molecular mechanism of banana seedlings adapted to the long-term MD condition.

Cerium-Promoted Ginsenosides Accumulation by Regulating Endogenous Methyl Jasmonate Biosynthesis in Hairy Roots of Panax ginseng

Among rare earth elements, cerium has the unique ability of regulating the growth of plant cells and the biosynthesis of metabolites at different stages of plant development. The signal pathways of Ce3+-mediated ginsenosides biosynthesis in ginseng hairy roots were investigated. At a low concentration, Ce3+ improved the elongation and biomass of hairy roots. The Ce3+-induced accumulation of ginsenosides showed a high correlation with the reactive oxygen species (ROS), as well as the biosynthesis of endogenous methyl jasmonate (MeJA) and ginsenoside key enzyme genes (PgSS, PgSE and PgDDS). At a Ce3+ concentration of 20 mg L-1, the total ginsenoside content was 1.7-fold, and the total ginsenosides yield was 2.7-fold that of the control. Malondialdehyde (MDA) content and the ROS production rate were significantly higher than those of the control. The activity of superoxide dismutase (SOD) was significantly activated within the Ce3+ concentration range of 10 to 30 mg L-1. The activity of catalase (CAT) and peroxidase (POD) strengthened with the increasing concentration of Ce3+ in the range of 20-40 mg L-1. The Ce3+ exposure induced transient production of superoxide anion (O2•-) and hydrogen peroxide (H2O2). Together with the increase in the intracellular MeJA level and enzyme activity for lipoxygenase (LOX), there was an increase in the gene expression level of MeJA biosynthesis including PgLOX, PgAOS and PgJMT. Our results also revealed that Ce3+ did not directly influence PgSS, PgSE and PgDDS activity. We speculated that Ce3+-induced ROS production could enhance the accumulation of ginsenosides in ginseng hairy roots via the direct stimulation of enzyme genes for MeJA biosynthesis. This study demonstrates a potential approach for understanding and improving ginsenoside biosynthesis that is regulated by Ce3+-mediated signal transduction.

Genome-wide comparative analysis of Mg transporter gene family between Triticum turgidum and Camelina sativa

Magnesium (Mg) as a bimetal plays critical roles in biochemical processes, membrane stability, and enzyme activity. Mg transporters (MGTs) are involving in maintaining Mg homeostasis in cells. Although the MGT family members have been identified in different plant species, there is no comprehensive analysis of the other plants' MGT genes. In the current study, 62 and 41 non-redundant putative MGT proteins were recognized into the genome of Camelina sativa, and Triticum turgidum and they were compared based on physicochemical properties, protein structure, expression, and interaction. All identified MGTs were classified into three subgroups, NIPA, CorA, and MRS2/MGT, based on conserved-motifs distribution. The results showed that the secondary structure pattern in NIPA and MRS2 subfamily members in both studied plant species were highly similar. Furthermore, MGTs encompass the conserved structures and the critical sites mainly in the metal ion and Mg²⁺ binding centers as well as the catalytic sites were observed. The highest numbers of protein channels were predicted in CorA proteins in both C. sativa and T. turgidum with 24 and 17 channel numbers, respectively. The Ser, Pro, Gly, Lys, Tyr, and Arg amino acids were predicted as the binding residues in MGTs channel regions. The expression pattern of identified genes demonstrated that MGT genes have diverse tissue-specific expression and stress response expression patterns. Besides, 147 co-expressed genes with MGTs were clustered into the eight co-expression nodes involved in N-glycan biosynthesis, protein processing in the endoplasmic reticulum, carbon metabolism, biosynthesis of amino acids, and endocytosis. In the present study, all interpretations are based on in silico predictions, which can be used in further studies related to functional genomics of MGT genes.

Ecological risk assessment of cerium for tropical agroecosystems

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC₅ = 281.6 mg Ce kg^-1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.

Cerium enhances germination and shoot growth, and alters mineral nutrient concentration in rice

Cerium (Ce) belongs to the rare earth elements (REEs), and although it is not essential for plants, it can stimulate growth and other physiological processes. The objective of this research was to evaluate the effect of Ce on seed germination, initial seedling growth, and vegetative growth in rice (Oryza sativa L.) cv. Morelos A-98. During the germination process, the seeds were treated with Ce concentrations of 0, 4, 8, and 12 μM; after 5 d, germination percentage was recorded and after 10 d seedling growth was measured. For vegetative growth, a hydroponic system was established where 14-d-old plants without previous Ce treatment were transferred into nutrient solution. After two weeks of acclimatizing, 0, 25, 50, and 100 μM Ce were added to the nutrient solution for 28 d. Ce significantly increased germination and the initial growth variables of the seedlings. During vegetative growth, Ce increased plant height, number of tillers, root volume, and shoot fresh and dry biomass, without affecting root biomass weight. With low Ce concentrations (25 and 50 μM), the concentrations of chlorophylls and amino acids in the shoots were similar to those in the control, like amino acid concentration in the roots at a concentration of 25 μM Ce. Conversely, the concentration of total sugars increased in the shoot with the application of 25, 50, and 100 μM Ce, and in the roots with the application of 50 μM Ce. Also, Ce did not affect the concentration of macro or micronutrients in the shoots. However, in the roots, the high Ce concentration decreased the concentrations of Ca, Fe, Mn, and Zn, while the Mg concentration increased. Our results indicate that Ce, at the right concentrations, can function as a biostimulant in rice germination and growth.

Magnesium-deficiency-induced alterations of gas exchange, major metabolites and key enzymes differ among roots, and lower and upper leaves of Citrus sinensis seedlings

Magnesium (Mg)-deficiency is a widespread problem adversely affecting the quality and yield of crops, including citrus. 'Xuegan' [Citrus sinensis (L.) Osbeck] seedlings were irrigated every other day with nutrient solution at an Mg concentration of 0 mM (Mg-deficiency) or 1 mM (Mg-sufficiency) for 16 weeks. Thereafter, biomass, leaf mass per area, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), pigments in the upper and lower leaves, Mg, gas exchange, organic acids, nonstructural carbohydrates, total soluble proteins, amino acids, phenolics and anthocyanins, and key enzymes related to organic acid, amino acid and phenolic metabolisms in the roots, and upper and lower leaves were assayed in order to test the hypothesis that Mg-deficiency-induced alterations of gas exchange, major metabolites and key enzymes may differ among the roots, and upper and lower leaves. Magnesium-deficiency affected the most measured parameters more in the lower than in the upper leaves except for the nonstructural carbohydrates, but the variation trends were similar between the two. Despite increased accumulation of nonstructural carbohydrates, the lower CO2 assimilation in the Mg-deficient leaves was not caused by the feedback inhibition mechanism via sugar accumulation. Both dark respiration and organic acid metabolism were elevated in the Mg-deficient lower leaves to 'consume' the excess carbohydrates, and inhibited in the Mg-deficient roots with less accumulation of nonstructural carbohydrates to keep the balance of net carbon. More total phenolics and fewer anthocyanins were accumulated in the Mg-deficient lower leaves, whereas the accumulation of both total phenolics and anthocyanins was reduced in the Mg-deficient roots. Interestingly, amino acid biosynthesis was repressed in the Mg-deficient roots and lower leaves, thus lowering the level of total free amino acids in these roots and leaves. To conclude, great differences existed in the Mg-deficiency-induced alterations of gas exchange, major metabolites and key enzymes among the roots, and upper and lower leaves.

Glutamine synthetase activity in leaves of Zea mays L. as influenced by magnesium status

The total capacity of the GS-mediated ligation of free ammonium and glutamate to form glutamine in the leaves of maize plants is not impaired upon severe magnesium starvation. Magnesium deficiency does not obligatorily lead to the decreased total protein concentrations in the leaves. Magnesium (Mg) is an integral component of the enzyme glutamine synthetase (GS), having both a structural and a catalytic role. Moreover, Mg is relevant for the post-translational regulation of the GS. Glutamine synthetase is one of the key enzymes in nitrogen assimilation, ligating-free ammonium (NH4 (+)) to glutamate to form glutamine and it is therefore crucial for plant growth and productivity. This study was conducted in order to test whether a severe Mg-deficiency impairs the total capacity of the GS-catalyzed synthesis of glutamine in maize leaves. Maize was grown hydroponically and the GS activity was analyzed dependent on different leaf developmental stages. Glutamine synthetase activity in vitro assays in combination with immune-dot blot analysis revealed that both the total activity and the abundance of glutamine synthetase was not impaired in the leaves of maize plants upon 54 days of severe Mg starvation. Additionally, it was shown that Mg deficiency does not obligatorily lead to decreased total protein concentrations in the leaves, as assayed by Bradford protein quantification. Moreover, Mg resupply to the roots or the leaves of Mg-deficient plants reversed the Mg-deficiency-induced accumulation of free amino acids in older leaves, which indicates impaired phloem loading. The results of our study reveal that the total GS-mediated primary or secondary assimilation of free NH4 (+) is not a limiting enzymatic reaction under Mg deficiency and thus cannot be accountable for the observed restriction of plant growth and productivity in Mg-deficient maize.

Use of lanthanides to alleviate the effects of metal ion-deficiency in Desmodesmus quadricauda (Sphaeropleales, Chlorophyta)

Lanthanides are biologically non-essential elements with wide applications in technology and industry. Their concentration as environmental contaminants is, therefore, increasing. Although non-essential, lanthanides have been proposed (and even used) to produce beneficial effects in plants, even though their mechanisms of action are unclear. Recently, it was suggested that they may replace essential elements. We tested the effect of low concentrations of lanthanides on the common freshwater microalga Desmodesmus quadricauda, grown under conditions of metal ion-deficiency (lower calcium or manganese concentrations). Our goal was to test if lanthanides can replace essential metals in their functions. Physiological stress was recorded by studying growth and photosynthetic activity using a pulse amplitude modulation (PAM) fluorimeter. We found that nutrient stress reduced parameters of growth and photosynthesis, such as maximal quantum yield, relative electron transport rate, photon capturing efficiency and light saturation irradiance. After adding low concentrations of five lanthanides, we confirmed that they can produce a stimulatory effect on microalgae, depending on the nutrient (metal) deprivation. In the case of a calcium deficit, the addition of lanthanides partly alleviated the adverse effects, probably by a partial substitution of the element. In contrast, with manganese deprivation (and at even lower concentrations), lanthanides enhanced the deleterious effect on cellular growth and photosynthetic competence. These results show that lanthanides can replace essential elements, but their effects on microalgae depend on stress and the nutritional state of the microalgae, raising the possibility of environmental impacts at even low concentrations.

Uptake of CeO2 nanoparticles and its effect on growth of Medicago arborea In vitro plantlets

The present study analyzes some effects of nano-CeO2 particles on the growth of in vitro plantlets of Medicago arborea when the nanoceria was added to the culture medium. Various concentrations of nano-CeO2 and bulk ceric oxide particles in suspension form were introduced to the agar culture medium to compare the effects of nanoceria versus ceric oxide bulk material. Germination rate and shoot dry weight were not affected by the addition of ceric oxide to the culture media. Furthermore, no effects were observed on chlorophyll content (single-photon avalanche diode (SPAD) measurements) due to the presence of either nano- or micro-CeO2 in the culture medium. When low concentrations of nanoceria were added to the medium, the number of trifoliate leaves and the root length increased but the root dry weight decreased. Also the values of maximum photochemical efficiency of PSII (F(v)/F m) showed a significant decrease. Dark-adapted minimum fluorescence (F 0) significantly increased in the presence of 200 mg L(-1) nanoceria and 400 mg L(-1) bulk material. Root tissues were more sensitive to nanoceria than were the shoots at lower concentrations of nanoceria. A stress effect was observed on M. arborea plantlets due to cerium uptake.

Combined effect and mechanism of acidity and lead ion on soybean biomass

Heavy metal pollution and soil acidification are serious global environmental issues. The combined pollution from acidification and heavy metal has become a new environmental issue in regions where the two issues simultaneously occur. However, studies on combined pollution are still limited. In the current study, we investigated the combined effect and mechanism of acidity and heavy metal [lead ion (Pb(2+))] on soybean biomass as well as on growth, nitrogen nutrition, and antioxidant system in soybean roots. Results showed that the combined treatment with acidity and Pb(2+) decreased the soybean biomass. At pH 4.5, the soybean biomass in the combined treatment with acidity and 0.9 mmol L(-1) Pb(2+) was lower than that in the combined treatment with acidity and Pb(2+) at 0.3 or 1.5 mmol L(-1). This result was also observed at pH 3.5 and 3.0. The combined treatment with acidity and Pb(2+) also resulted in the following consequences: root growth inhibition; decrease in nitrate, ammonium, and malondialdehyde contents; increase in nitrite reductase activity; and decrease in peroxidase activity. The extent at which the test indexes decreased/increased in the combined treatment was higher than that in the single acidity treatment. The correlation analysis results indicated that the decrease in the soybean biomass in the combined treatment with acidity and Pb(2+) resulted from the decrease in the root growth, nitrate-nitrogen assimilation, and peroxidase activity.

Improvement of cerium on photosynthesis of maize seedlings under a combination of potassium deficiency and salt stress

Added Ce(3+) can partly substitute for Ca(2+) or Mg(2+) and improve photosynthesis under the deficiency of these elements, but very few studies focused on photosynthetic improvement in maize seedlings caused by K(+) deficiency, salt stress, especially a combination of K(+) deficiency and salt stress. In the present study, the effects of Ce(3+) on the photosynthesis of maize seedlings under the three different stresses were investigated. The results showed that added Ce(3+) under various stresses increased the ratios of free water/bound water and of K(+)/Na(+), the pigment contents, the values of Fv/Fm, Y(II), ETR(II), Y(NPQ), Qp, qL, NPQ, and qN of photosystem II (PSII), the values of Y(I) and ETR(I) of photosystem I (PSI) and the expression levels of LhcII cab1 and rbcL, and decreased the values of Y(NO) and Y(NA). This implied that added Ce(3+) depressed ion toxicity, photodamage of PSII, and acceptor side constraints of PSI, and enhanced adjustable energy dissipation, the responses of photochemistry, and carbon assimilation caused by K(+) deficiency, salt stress, and the combination of K(+) deficiency and salt stress. However, Ce(3+) mitigation of photosynthetic inhibition in maize seedlings caused by the combined stresses was greater than that of salt stress, and Ce(3+) mitigation under salt stress was greater than that under K(+) deficiency. In addition, the results also showed that Ce(3+) cannot improve photosynthesis and growth of maize seedlings under K(+) deficiency by substituting for K(+).

Lanthanum (III) regulates the nitrogen assimilation in soybean seedlings under ultraviolet-B radiation

Ultraviolet-B (UV-B, 280-320 nm) radiation has seriously affected the growth of plants. Finding the technology/method to alleviate the damage of UV-B radiation has become a frontal topic in the field of environmental science. The pretreatment with rare earth elements (REEs) is an effective method, but the regulation mechanism of REEs is unknown. Here, the regulation effects of lanthanum (La(III)) on nitrogen assimilation in soybean seedlings (Glycine max L.) under ultraviolet-B radiation were investigated to elucidate the regulation mechanism of REEs on plants under UV-B radiation. UV-B radiation led to the inhibition in the activities of the key enzymes (nitrate reductase, glutamine synthetase, glutamate synthase) in the nitrogen assimilation, the decrease in the contents of nitrate and soluble proteins, as well as the increase in the content of amino acid in soybean seedlings. The change degree of UV-B radiation at the high level (0.45 W m(-2)) was higher than that of UV-B radiation at the low level (0.15 W m(-2)). The pretreatment with 20 mg L(-1) La(III) could alleviate the effects of UV-B radiation on the activities of nitrate reductase, glutamine synthetase, glutamate synthase, and glutamate dehydrogenase, promoting amino acid conversion and protein synthesis in soybean seedlings. The regulation effect of La(III) under UV-B radiation at the low level was better than that of UV-B radiation at the high level. The results indicated that the pretreatment with 20 mg L(-1) La(III) could alleviate the inhibition of UV-B radiation on nitrogen assimilation in soybean seedlings.

Magnesium deficiency results in damage of nitrogen and carbon cross-talk of maize and improvement by cerium addition

Magnesium (Mg) deficiency has been reported to affect plant photosynthesis and growth, and cerium (Ce) was considered to be able to improve plant growth. However, the mechanisms of Mg deficiency and Ce on plant growth remain poorly understood. The main aim of this work is to identify whether or not Mg deprivation affects the interdependent nitrogen and carbon assimilations in the maize leaves and whether or not Ce modulates the assimilations in the maize leaves under Mg deficiency. Maize plants were cultivated in Hoagland’s solution. They were subjected to Mg deficiency and to cerium chloride administration in the Mg-present Hoagland’s media and Mg-deficient Hoagland’s media.After 2 weeks,we measured chlorophyll (Chl) a fluorescence and the activities of nitrate reductase (NR), sucrose-phosphate synthase(SPS), and phosphoenolpyruvate carboxylase (PEPCase)in metabolic checkpoints coordinating primary nitrogen and carbon assimilations in the maize leaves. The results showed that Mg deficiency significantly inhibited plant growth and decreased the activities of NR, SPS, and PEPCase and the synthesis of Chl and protein. Mg deprivation in maize also significantly decreased the oxygen evolution, electron transport,and efficiency of photochemical energy conversion by photosystem II (PSII). However, Ce addition may promote nitrogen and carbon assimilations, increase PSII activities,and improve maize growth under Mg deficiency. Moreover,our findings would help promote usage of Mg or Ce fertilizers in maize production.

Effect of lanthanum on rooting of in vitro regenerated shoots of Saussurea involucrata Kar. et Kir

In present study, the effect of lanthanum (La) on the rooting of regenerated shoots of Saussurea involucrata Kar. et Kir was analyzed. Rooting occurred from regenerated shoots inoculated on a medium supplemented with La, the plant rooting hormone indole-3-acetic acid (IAA), or both La and IAA together. The highest rooting efficiency (96%), root number/shoot (8.5), and root length (63 mm) were recorded in shoots cultured on medium containing 2.5 μM IAA combined with 100 μM La(3+). In order to elucidate the mechanism of rooting enhancement by La, we examined dynamic changes in antioxidant enzyme activities in plant tissue over time in culture. We found that the activities of peroxidase (POX) and superoxide dismutase (SOD) were significantly higher in plant tissue cultured in IAA plus La than in La or IAA alone. At the same time, the highest H(2)O(2) content was detected in plant tissue in the presence of 2.5 μM IAA plus 100 μM La(3+). In light of these data and previous results, we speculate that La enhanced IAA-induced rooting by acting as a mild abiotic stress to stimulate POX and SOD activities in plant cells. Then, IAA reacted with oxygen and POX to form the ternary complex enzyme-IAA-O(2) that dissociated into IAA radicals and O(2)(-). Subsequently, IAA-induced O(2)(-) readily converted to hydroxyl radical (HO·) via SOD-catalyzed dismutation. Finally, cell wall loosening and cell elongation occurred as a consequence of HO-dependent scission of wall components, leading to root growth. The treatment of IAA combined with La resulted in the highest plantlet survival (80%) compared to single treatments with IAA or La alone. These data suggest that rare earth elements enhance root morphogenesis and the growth of S. involucrata.

Effects of manganese deficiency and added cerium on nitrogen metabolism of maize

Manganese is one of the essential microelements for plant growth, and cerium is a beneficial element for plant growth. However, whether manganese deficiency affects nitrogen metabolism of plants and cerium improves the nitrogen metabolism of plants by exposure to manganese-deficient media are still unclear. The main aim of the study was to determine the effects of manganese deficiency in nitrogen metabolism and the roles of cerium in the improvement of manganese-deficient effects in maize seedlings. Maize seedlings were cultivated in manganese present Meider's nutrient solution. They were subjected to manganese deficiency and to cerium chloride administered in the manganese-present and manganese-deficient media. Maize seedlings grown in the various media were measured for key enzyme activities involved in nitrogen metabolism, such as nitrate reductase, glutamate dehydrogenase, glutamine synthetase, and glutamic-oxaloace transaminase. We found that manganese deficiency restricted uptake and transport of NO(3)(-), inhibited activities of nitrogen-metabolism-related enzymes, such as nitrate reductase, glutamine synthetase, and glutamic-oxaloace transaminase, thus decreasing the synthesis of chlorophyll and soluble protein, and inhibited the growth of maize seedlings. Manganese deficiency promoted the activity of glutamate dehydrogenase and reduced the toxicity of excess ammonia to the plant, while added cerium relieved the damage to nitrogen metabolism caused by manganese deficiency in maize seedlings. However, cerium addition exerted positively to relieve the damage of nitrogen metabolism process in maize seedlings caused by exposure to manganese-deficient media.

Cerium relieves the inhibition of chlorophyll biosynthesis of maize caused by magnesium deficiency

Lanthanoids (Ln) were demonstrated to improve chlorophyll formation and the growth of plants. But the mechanism of the fact that Ln promotes chlorophyll biosynthesis of plants is poorly understood. The main aim of the study was to determine Ln effects in chlorophyll formation of maize under magnesium (Mg) deficiency. Maize plants were cultivated in Hoagland's solution. They were subjected to Mg deficiency and to cerium administered in Mg-deficient Hoagland's media, and then the contents of various chlorophyll precursors and gen expressions of the key enzymes of chlorophyll biosynthesis were examined. The decrease of chlorophyll contents in maize leaves caused by Mg deficiency suggested an inhibition of chlorophyll synthesis that was inhibited by a reduction of the precursors as measured by analyzing the contents of δ-aminolevulinic acid, porphobilinogen, uroporphyrinogen III, Mg-protoporphyrin IX, and protochlorophyll, as well as the expression levels of magnesium chelatase, magnesium-protoporphyrin IX methyltransferase, and chlorophyll synthase; Mg deficiency significantly inhibited the transformation from coproporphyrinogen III or protoporphyrin IX to chlorophyll. However, cerium addition significantly relieved the inhibition of chlorophyll biosynthesis in maize caused by Mg deficiency and increased chlorophyll content and promoted a series of transformations from δ-aminolevulinic acid to chlorophyll and maize growth under Mg deficiency. It implied that cerium might partly substitute for the role of Mg.

Effects of lanthanum on calcium and magnesium contents and cytoplasmic streaming of internodal cells of Chara corallina

Biological and environmental effects of lanthanide series of elements have received much attention recently due to their wide applications. In this study, effects of La(3+) treatments on calcium and magnesium concentrations as well as cytoplasmic streaming of internodal cells of Chara corallina were investigated. At all treatment concentrations (10, 100, and 1,000 μM), La(3+) significantly decreased calcium concentrations in the cell-wall fractions after 5-h treatments. Calcium concentrations in the cell contents and magnesium concentrations in the cell-wall fractions were reduced by 100 and 1,000 μM La(3+) treatments. However, cytoplasmic streaming as an indicator of [Ca(2+)](cyt) was only inhibited at the highest La(3+) concentration (1,000 μM). The results suggest that La(3+) may affect cellular calcium homeostasis by actions other than as a simple Ca(2+) antagonist. La(3+) could partially compensate for calcium deficiency at certain concentrations.

Improvement of cerium of photosynthesis functions of maize under magnesium deficiency

Rare earth elements can promote photosynthesis, but their mechanisms are still poorly understood under magnesium deficiency. The present study was designed to determine the role of cerium in magnesium-deficient maize plants. Maize was cultivated in Hoagland's solution added with cerium with and without adequate quantities of magnesium. Under magnesium-deficient conditions, cerium can prevents inhibition of synthesis of photosynthetic pigment, improves light energy absorption and conversion, oxygen evolution, and the activity of photo-phosphorelation and its coupling factor Ca(2+)-ATPase. These results suggest that cerium could partly substitute magnesium, improving photosynthesis and plant growth.

Potassium chloride and rare earth elements improve plant growth and increase the frequency of the Agrobacterium tumefaciens-mediated plant transformation

Plant transformation efficiency depends on the ability of the transgene to successfully interact with plant host factors. Our previous work and the work of others showed that manipulation of the activity of host factors allows for increased frequency of transformation. Recently we reported that exposure of tobacco plants to increased concentrations of ammonium nitrate increases the frequency of both homologous recombination and plant transgenesis. Here we tested the influence of KCl and salts of rare earth elements, Ce and La on the efficiency of Agrobacterium-mediated plant transformation. We found that exposure to KCl, CeCl(3) and LaCl(3) leads to an increase in recombination frequency in Arabidopsis and tobacco. Plants grown in the presence of CeCl(3) and LaCl(3) had higher biomass, longer roots and greater root number. Analysis of transformation efficiency showed that exposure of tobacco plants to 50 mM KCl resulted in ~6.0-fold increase in the number of regenerated calli and transgenic plants as compared to control plants. Exposure to various concentrations of CeCl(3) showed a maximum increase of ~3.0-fold in both the number of calli and transgenic plants. Segregation analysis showed that exposure to KCl and cerium (III) chloride leads to more frequent integrations of the transgene at a single locus. Analysis of transgene intactness showed better preservation of right T-DNA border during transgene integration. Our data suggest that KCl and CeCl(3) can be effectively used to improve quantity and quality of transgene integrations.