Critical Leaf Magnesium Thresholds and the Impact of Magnesium on Plant Growth and Photo-Oxidative Defense: A Systematic Review and Meta-Analysis From 70 Years of Research

Genome-wide identification of MGT gene family in soybean (Glycine max) and their expression analyses under magnesium stress conditions

BACKGROUND

Magnesium (Mg) is essential for plant growth and development and plays critical roles in physiological and biochemical processes. Mg deficiency adversely affects growth of plants by limiting shoot and root development, disturbing the structure and membranes of the grana, reducing photosynthesis efficiency, and lowering net CO2 assimilation. The MGT (Magnesium transporter) family is responsible for the absorption and transportation of magnesium in plants. Although the MGT family has been identified in different plant species, research regarding the soybean MGT genes is limited.

RESULTS

In the current study, a total of 39 MGT genes distributed on 17 different chromosomes were identified in soybean. Phylogenetic analysis classified GmMGTs into three subgroups, NIPA, MRS2/MGT, and CorA, which showed little homology with MGTs of Arabidopsis thaliana and Oryza sativa members and clustered tightly with GmMGTs. Gene structure and conserved motif analysis also confirmed similar grouping in GmMGTs. The expansion of the GmMGT members in NIPA and MRS2/MGT was predicted, while CorA was identified as the most conserved group in G. max. Segmental duplication under purifying selection pressure was identified as the major driving force in the expansion of MGTs in soybean. GmMGTs showed diverse tissue-specific and stress-response expression patterns due to the presence of stress-related cis-regulatory elements in their promoter regions. Under Mg-deficiency and surplus stress conditions, a decrease in root length, shoot length, and root and shoot fresh as well dry weight in susceptible genotypes showed the variegated expression of MGTs in soybean genotypes. Furthermore, the upregulation of GmMGT2 and GmMGT29 in tolerant genotypes in response to Mg-deficiency as well as surplus stress conditions in leaves suggested the essential role of GmMGT genes in the absorption and transportation of Mg in soybean leaves.

CONCLUSION

This study presents a comprehensive analysis of the MGT gene family in soybean, providing insights into their evolutionary relationships, gene classification, protein structures, and expression patterns under both Mg deficiency and Mg surplus conditions.

Integrative transcriptomic analysis reveals the molecular responses of tobacco to magnesium deficiency

Introduction

Magnesium (Mg) is a crucial macronutrient for plants. Understanding the molecular responses of plants to different levels of Mg supply is important for improving cultivation practices and breeding new varieties with efficient Mg utilization.

Methods

In this study, we conducted a comprehensive transcriptome analysis on tobacco (Nicotiana tabacum L.) seedling leaves to investigate changes in gene expression in response to different levels of Mg supply, including Mg-deficient, 1/4-normal Mg, normal Mg, and 4×-normal Mg, with a particular focus on Mg deficiency at 5, 15 and 25 days after treatment (DAT), respectively.

Results

A total of 11,267 differentially expressed genes (DEGs) were identified in the Mg-deficient, 1/4-normal Mg, and/or 4×-normal Mg seedlings compared to the normal Mg seedlings. The global gene expression profiles revealed potential mechanisms involved in the response to Mg deficiency in tobacco leaves, including down-regulation of genes-two DEGs encoding mitochondria-localized NtMGT7 and NtMGT9 homologs, and one DEG encoding a tonoplast-localized NtMHX1 homolog-associated with Mg trafficking from the cytosol to mitochondria and vacuoles, decreased expression of genes linked to photosynthesis and carbon fixation at later stages, and up-regulation of genes related to antioxidant defenses, such as NtPODs, NtPrxs, and NtGSTs.

Discussion

Our findings provide new insights into the molecular mechanisms underlying how tobacco responds to Mg deficiency.

Receptor-like cytoplasmic kinase 58 reduces tolerance of maize seedlings to low magnesium via promoting H2O2 over-accumulation

KEY MESSAGE

ZmRLCK58, a negative growth regulator, reduces tolerance of maize seedlings to low Mg via enhancing H2O2 accumulation in the shoot. Magnesium (Mg) deficiency is one of critical limiting factors for crop production in widespread acidic soils worldwide. However, the molecular mechanism of crop response to Mg deficiency is still largely unclear. Here, we found higher concentrations of H2O2, soluble sugars, and starch (1.5-, 1.9-, and 1.4-fold, respectively) in the shoot of low-Mg-treated maize seedlings, compared with Mg sufficient plants under hydroponic culture. Consistent with over-accumulation of H2O2, transcriptome profiling revealed significant enrichment of 175 differentially expressed genes (DEGs) in "response to oxygen-containing compound" out of 641 DEGs in the shoot under low Mg. Among 175 DEGs, a down-regulated receptor-like cytoplasmic kinase ZmRLCK58 underwent a recent duplication event before Poaceae divergence and was highly expressed in the maize shoot. ZmRLCK58 overexpression enhanced H2O2 accumulation in shoots by 21.3% and 29.8% under control and low-Mg conditions, respectively, while reducing biomass accumulation compared with wild-type plants. Low Mg further led to 39.7% less starch accumulation in the ZmRLCK58 overexpression shoot and lower Mg utilization efficiency. Compared with wild-type plants, overall down-regulated expression of genes related to response to carbohydrate, photosynthesis, H2O2 metabolic, oxidation-reduction, and ROS metabolic processes in ZmRLCK58 overexpression lines preconditioned aforementioned physiological alterations. Together, ZmRLCK58, as a negative growth regulator, reduces tolerance of maize seedlings to low Mg via enhancing H2O2 accumulation.

Potential of Castanea sativa for biomonitoring As, Hg, Pb, and Tl: A focus on their distribution in plant tissues from a former mining district

Bioavailability of potentially toxic elements (PTEs) from the Earth's crust in the soil, e.g., As, Hg, Tl, and Pb, can pose a potential environmental and health risk because of human activities, especially related to mining extraction. The biomonitoring allows to detect PTE contamination through their measurement in living organisms as trees. However, the choice of which plant species and tissue to analyse is a key point to be evaluated in relation to PTE absorption and translocation. The aim of this work was to assess the As, Hg, Tl, and Pb distribution in Castanea sativa Mill. plant tissues, given its importance for both biomass and food production. The study identified two sites in the Alpi Apuane (Italy), with similar environmental conditions (e.g., elevation, exposure, forest type, and tree species) but different soil PTE levels. The topsoil was characterized, and the PTE fractions with different bioavailability were measured. The PTE concentrations were also analysed in chestnut plant tissues (leaves, bark, wood, nuts, and shells) in parallel with and evaluation of plant health status through the determination of micro and macronutrient concentrations and the leaf C and N isotope composition (δ13C or δ15N). Chestnut trees showed a good health status highlighting its suitability for Tl, As, Hg, and Pb biomonitoring, displaying a tissue-specific PTE allocation. Thallium and Hg were detected in all plant tissues at similar concentrations, As was found in leaves, wood, and nuts while Pb only in the bark. The δ15N negatively correlated with leaf Mn and Tl concentrations, suggesting possible changes in N source and/or plant metabolism due to the high contamination level and acid soil pH. Thallium in La Culla site trees was associated with its presence in the carbonate rocks but not in the topsoil, highlighting the potentiality of chestnut in providing valuable information for geochemical surveying.

The role of magnesium oxide foliar sprays in enhancing mint (Mentha crispa L.) tolerance to cadmium stress

This study investigates using magnesium foliar spray to enhance mint plants' growth and physiological performance under cadmium toxicity. It examines the effects of foliar application of magnesium oxide (40 mg L-1), in both nano and bulk forms, on mint plants exposed to cadmium stress (60 mg kg-1 soil). Cadmium stress reduced root growth and activity, plant biomass (32%), leaf hydration (19%), chlorophyll levels (27%), magnesium content (51%), and essential oil yield (35%), while increasing oxidative and osmotic stress in leaf tissues. Foliar application of magnesium increased root growth (32%), plant biomass, essential oil production (17%), leaf area (24%), chlorophyll content (10%), soluble sugar synthesis (33%), and antioxidant enzyme activity, and reduced lipid peroxidation and osmotic stress. Although the nano form of magnesium enhanced magnesium absorption, its impact on growth and physiological performance was not significantly different from the bulk form. Therefore, foliar application of both forms improves plants' ability to withstand cadmium toxicity. However, the study is limited by its focus on a single plant species and specific environmental conditions, which may affect the generalizability of the results. The long-term sustainability of such treatments could provide a more comprehensive understanding of magnesium's role in mitigating heavy metal stress in plants.

Transcription-related metabolic regulation in grafted lemon seedlings under magnesium deficiency stress

Magnesium is one of the essential nutrients for plant growth, and plays a pivotal role in plant development and metabolism. Soil magnesium deficiency is evident in citrus production, which ultimately leads to failure of normal plant growth and development, as well as decreased productivity. Citrus is mainly propagated by grafting, so it is necessary to fully understand the different regulatory mechanisms of rootstock and scion response to magnesium deficiency. Here, we characterized the differences in morphological alterations, physiological metabolism and differential gene expression between trifoliate orange rootstocks and lemon scions under normal and magnesium-deficient conditions, revealing the different responses of rootstocks and scions to magnesium deficiency. The transcriptomic data showed that differentially expressed genes were enriched in 14 and 4 metabolic pathways in leaves and roots, respectively, after magnesium deficiency treatment. And the magnesium transport-related genes MHX and MRS2 may respond to magnesium deficiency stress. In addition, magnesium deficiency may affect plant growth by affecting POD, SOD, and CAT enzyme activity, as well as altering the levels of hormones such as IAA, ABA, GA3, JA, and SA, and the expression of related responsive genes. In conclusion, our research suggests that the leaves of lemon grafted onto trifoliate orange were more significantly affected than the roots under magnesium-deficient conditions, further indicating that the metabolic imbalance of scion lemon leaves was more severe.

From power to plants: unveiling the environmental footprint of lithium batteries

Widespread adoption of lithium-ion batteries in electronic products, electric cars, and renewable energy systems has raised severe worries about the environmental consequences of spent lithium batteries. Because of its mobility and possible toxicity to aquatic and terrestrial ecosystems, lithium, as a vital component of battery technology, has inherent environmental problems. Leaching of lithium from discharged batteries, as well as its subsequent migration through soil and water, represents serious environmental hazards, since it accumulates in the food chain, impacting ecosystems and human health. This study thoroughly analyses the effects of lithium on plants, including its absorption, transportation, and toxicity. An attempt has been made to examine how lithium moves throughout plants through symplastic and apoplastic pathways and the factors that affect lithium accumulation in plant tissues, such as soil pH and calcium. This review focuses on the possible toxicity of lithium and its impact on ecosystems and human health. Aside from examining the environmental impacts, this review also emphasizes the significance of proper disposal and recycling measures in order to offset the negative effects of used lithium batteries. The paper also highlights the need for ongoing research to develop innovative and sustainable techniques for lithium recovery and remediation.

Photosynthetic plasticity aggravates the susceptibility of magnesium-deficient leaf to high light in rapeseed plants: the importance of Rubisco and mesophyll conductance

Plants grown under low magnesium (Mg) soils are highly susceptible to encountering light intensities that exceed the capacity of photosynthesis (A), leading to a depression of photosynthetic efficiency and eventually to photooxidation (i.e., leaf chlorosis). Yet, it remains unclear which processes play a key role in limiting the photosynthetic energy utilization of Mg-deficient leaves, and whether the plasticity of A in acclimation to irradiance could have cross-talk with Mg, hence accelerating or mitigating the photodamage. We investigated the light acclimation responses of rapeseed (Brassica napus) grown under low- and adequate-Mg conditions. Magnesium deficiency considerably decreased rapeseed growth and leaf A, to a greater extent under high than under low light, which is associated with higher level of superoxide anion radical and more severe leaf chlorosis. This difference was mainly attributable to a greater depression in dark reaction under high light, with a higher Rubisco fallover and a more limited mesophyll conductance to CO2 (gm ). Plants grown under high irradiance enhanced the content and activity of Rubisco and gm to optimally utilize more light energy absorbed. However, Mg deficiency could not fulfill the need to activate the higher level of Rubisco and Rubisco activase in leaves of high-light-grown plants, leading to lower Rubisco activation and carboxylation rate. Additionally, Mg-deficient leaves under high light invested more carbon per leaf area to construct a compact leaf structure with smaller intercellular airspaces, lower surface area of chloroplast exposed to intercellular airspaces, and CO2 diffusion conductance through cytosol. These caused a more severe decrease in within-leaf CO2 diffusion rate and substrate availability. Taken together, plant plasticity helps to improve photosynthetic energy utilization under high light but aggravates the photooxidative damage once the Mg nutrition becomes insufficient.

Inhibitory impact of MgO nanoparticles on oxidative stress and other physiological attributes of spinach plant grown under field condition

Green synthesis of NPs is preferred due to its eco-friendly procedures and non-toxic end products. However, unintentional release of NPs can lead to environmental pollution affecting living organisms including plants. NPs accumulation in soil can affect the agricultural sustainability and crop production. In this context, we report the morphological and biochemical response of spinach nanoprimed with MgO-NPs at concentrations, 10, 50, 100, and 150 µg/ml. Nanopriming reduced the spinach root length by 14-26%, as a result a reduction of 20-74% in the length of spinach shoots was observed. The decreased spinach shoot length inhibited the chlorophyll accumulation by 21-55%, thus reducing the accumulation of carbohydrates and yield by 46 and 49%, respectively. The reduced utilization of the total absorbed light further enhanced ROS generation and oxidative stress by 32%, thus significantly altering their antioxidant system. Additionally, a significant variation in the accumulation of flavonoid pathway downstream metabolites myricitin, rutin, kaempferol-3 glycoside, and quercitin was also revealed on MgO-NPs nanopriming. Additionally, NPs enhanced the protein levels of spinach probably as an osmoprotectant to regulate the oxidative stress. However, increased protein precipitable tannins and enhanced oxidative stress reduced the protein digestibility and solubility. Overall, MgO-NPs mediated oxidative stress negatively affected the growth, development, and yield of spinach in fields in a concentration dependent manner.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s12298-023-01391-9.

Nutritional Content and Microbial Load of Fresh Liang, Gnetum gnemon var. tenerum Leaves

Liang (Gnetum gnemon var. tenerum) leaves are widely consumed as a green vegetable in Southern Thailand, and the plant is valued for its nutritional benefits. However, like other leafy greens, liang is vulnerable to microbial contamination, generating foodborne illnesses. This study examined the nutritional content and microbial load of liang leaves at different maturity stages and the effects of washing with chlorinated water. Various growth stages were analysed for proximate composition, amino acids, vitamins, and minerals. Results revealed distinct nutritional profiles, with tip leaves rich in protein and fat and intermediate leaves high in dietary fibre. Liang leaves are abundant in essential amino acids and proteins. Washing with chlorinated water increased leaf weight due to water retention but also caused physical damage, fostering microbial growth and spoilage. Microbiological analysis showed marginal reductions in total viable counts after washing with chlorinated water and significant decreases in coliform and Escherichia coli counts. However, stem detachment during washing increased the coliform and E. coli counts. Liang leaves exhibited favourable nutritional content, especially in the intermediate stage. Proper handling and storage of liang leaves are crucial to preventing physical damage and microbial contamination. Improved food safety measures, including appropriate post-harvest washing and handling of leafy vegetables, will ensure that consumers can safely enjoy the nutritional benefits of liang leaves.

Magnesium supply alleviates iron toxicity-induced leaf bronzing in rice through exclusion and tissue-tolerance mechanisms

Introduction

Iron (Fe) toxicity is a widespread nutritional disorder in lowland rice causing growth retardation and leaf symptoms referred to as leaf bronzing. It is partly caused by an imbalance of nutrients other than Fe and supply of these is known to mitigate the toxicity. But the physiological and molecular mechanisms involved are unknown.

Methods

We investigated the effect of magnesium (Mg) on Fe toxicity tolerance in a field study in the Central Highlands of Madagascar and in hydroponic experiments with excess Fe (300 mg Fe L-1). An RNA-seq analysis was conducted in a hydroponic experiment to elucidate possible mechanisms underlying Mg effects.

Results and discussion

Addition of Mg consistently decreased leaf bronzing under both field and hydroponic conditions, whereas potassium (K) addition caused minor effects. Plants treated with Mg tended to have smaller shoot Fe concentrations in the field, suggesting enhanced exclusion at the whole-plant level. However, analysis of multiple genotypes showed that Fe toxicity symptoms were also mitigated without a concomitant decrease of Fe concentration, suggesting that increased Mg supply confers tolerance at the tissue level. The hydroponic experiments also suggested that Mg mitigated leaf bronzing without significantly decreasing Fe concentration or oxidative stress as assessed by the content of malondialdehyde, a biomarker for oxidative stress. An RNA-seq analysis revealed that Mg induced more changes in leaves than roots. Subsequent cis-element analysis suggested that NAC transcription factor binding sites were enriched in genes induced by Fe toxicity in leaves. Addition of Mg caused non-significant enrichment of the same binding sites, suggesting that NAC family proteins may mediate the effect of Mg. This study provides clues for mitigating Fe toxicity-induced leaf bronzing in rice.

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.

Widely targeted metabolomic profiling combined with transcriptome analysis sheds light on flavonoid biosynthesis in sweet orange 'Newhall' (C. sinensis) under magnesium stress

Sweet orange 'Newhall' peels (SOPs) are abundant in flavonoids, making them increasingly popular in the realms of nutrition, food, and medicine. However, there is still much unknown about flavonoid components in SOPs and the molecular mechanism of flavonoid biosynthesis when subjected to magnesium stress. The previous experiment conducted by the research group found that the total flavonoid content of Magnesium deficiency (MD) was higher than Magnesium sufficiency (MS) in SOPs. In order to study the metabolic pathway of flavonoids under magnesium stress, an integrative analysis of the metabolome and transcriptome was performed in SOPs at different developmental stages, comparing MS and MD. A comprehensive analysis revealed the identification of 1,533 secondary metabolites in SOPs. Among them, 740 flavonoids were classified into eight categories, with flavones identified as the dominant flavonoid component. The influence of magnesium stress on flavonoid composition was evaluated using a combination of heat map and volcanic map, which indicated significant variations between MS and MD varieties at different growth stages. The transcriptome detected 17,897 differential genes that were significantly enriched in flavonoid pathways. Further analysis was performed using Weighted gene correlation network analysis (WGCNA) in conjunction with flavonoid metabolism profiling and transcriptome analysis to identify six hub structural genes and ten hub transcription factor genes that play a crucial role in regulating flavonoid biosynthesis from yellow and blue modules. The correlation heatmap and Canonical Correspondence Analysis (CCA) results showed that CitCHS had a significant impact on the synthesis of flavones and other flavonoids in SOPs, as it was the backbone gene in the flavonoid biosynthesis pathway. The qPCR results further validated the accuracy of transcriptome data and the reliability of candidate genes. Overall, these results shed light on the composition of flavonoid compounds in SOPs and highlight the changes in flavonoid metabolism that occur under magnesium stress. This research provides valuable insights for improving the cultivation of high-flavonoid plants and enhancing our understanding of the molecular mechanisms underlying flavonoid biosynthesis.

Quantitative elemental imaging in eukaryotic algae

All organisms, fundamentally, are made from the same raw material, namely the elements of the periodic table. Biochemical diversity is achieved by how these elements are utilized, for what purpose, and in which physical location. Determining elemental distributions, especially those of trace elements that facilitate metabolism as cofactors in the active centers of essential enzymes, can determine the state of metabolism, the nutritional status, or the developmental stage of an organism. Photosynthetic eukaryotes, especially algae, are excellent subjects for quantitative analysis of elemental distribution. These microbes utilize unique metabolic pathways that require various trace nutrients at their core to enable their operation. Photosynthetic microbes also have important environmental roles as primary producers in habitats with limited nutrient supplies or toxin contaminations. Accordingly, photosynthetic eukaryotes are of great interest for biotechnological exploitation, carbon sequestration, and bioremediation, with many of the applications involving various trace elements and consequently affecting their quota and intracellular distribution. A number of diverse applications were developed for elemental imaging, allowing subcellular resolution, with X-ray fluorescence microscopy (XFM, XRF) being at the forefront, enabling quantitative descriptions of intact cells in a non-destructive method. This Tutorial Review summarizes the workflow of a quantitative, single-cell elemental distribution analysis of a eukaryotic alga using XFM.

The sensitivity of photosynthesis to magnesium deficiency differs between rice (Oryza sativa L.) and cucumber (Cucumis sativus L.)

Magnesium is an essential macronutrient for plant photosynthesis, and in response to Mg deficiency, dicots appear more sensitive than monocots. Under Mg deficiency, we investigated the causes of differing photosynthetic sensitivities in a dicot and a monocot species. Rice (Oryza sativa L.) and cucumber (Cucumis sativus L.) were grown in hydroponic culture to explore their physiological responses to Mg deficiency stress. Both Mg-deficient rice and cucumber plants exhibited lower biomass, leaf area, Mg concentration, and chlorophyll content (Chl) compared with Mg-sufficient plants. However, a more marked decline in Chl and carotenoid content (Car) occurred in cucumber. A lower CO2 concentration in chloroplasts (C c) was accompanied by a decrease in the maximum rate of electron transport (J max) and the maximum rate of ribulose 1,5-bisphosphate carboxylation (V cmax), restricting CO2 utilization in Mg-deficient plants. Rice and cucumber photorespiration rate (P r) increased under Mg deficiency. Additionally, for cucumber, Car and non-photochemical quenching (NPQ) were reduced under lower Mg supply. Meanwhile, cucumber Mg deficiency significantly increased the fraction of absorbed light energy dissipated by an additional quenching mechanism (Φf,D). Under Mg deficiency, suppressed photosynthesis was attributed to comprehensive restrictions of mesophyll conductance (g m), J max, and V cmax. Cucumber was more sensitive to Mg deficiency than rice due to lower NPQ, higher rates of electron transport to alternative pathways, and subsequently, photooxidation damage.

Efficient Somatic Embryogenesis, Regeneration and Acclimatization of Panax ginseng Meyer: True-to-Type Conformity of Plantlets as Confirmed by ISSR Analysis

Panax ginseng Meyer grows in east Russia and Asia. There is a high demand for this crop due to its medicinal properties. However, its low reproductive efficiency has been a hindrance to the crop's widespread use. This study aims to establish an efficient regeneration and acclimatization system for the crop. The type of basal media and strength were evaluated for their effects on somatic embryogenesis, germination, and regeneration. The highest rate of somatic embryogenesis was achieved for the basal media MS, N6, and GD, with the optimal nitrogen content (≥35 mM) and NH₄⁺/NO₃^- ratio (1:2 or 1:4). The full-strength MS medium was the best one for somatic embryo induction. However, the diluted MS medium had a more positive effect on embryo maturation. Additionally, the basal media affected shooting, rooting, and plantlet formation. The germination medium containing 1/2 MS facilitated good shoot development; however, the medium with 1/2 SH yielded outstanding root development. In vitro-grown roots were successfully transferred to soil, and they exhibited a high survival rate (86.3%). Finally, the ISSR marker analysis demonstrated that the regenerated plants were not different from the control. The obtained results provide valuable information for a more efficient micropropagation of various P. ginseng cultivars.

A novel bud mutant of navel orange (Citrus sinensis) shows tolerance to chlorosis in acidic and magnesium-deficient soils

Interveinal chlorosis in old leaves is a common occurrence in citrus orchards in southern China. The present study investigates the 'Langfeng' navel orange (LF, Citrus sinensis) grafted onto a Trifoliate orange (TO, Poncirus trifoliata) rootstock, which exhibits healthy green leaves, and the 'Newhall' navel orange (NHE, C. sinensis) grafted onto TO, which has typical magnesium (Mg) deficiency-induced chlorosis. Chemical analysis of the rhizosphere soil revealed that the pH values were around 3.92 and that both Mg and calcium (Ca) were significantly deficient in the rhizosphere soil of both grafting combinations (LF/TO and NHE/TO). Furthermore, the chlorotic leaves of NHE/TO had significantly lower levels of Mg, Ca, and phosphorus (P), and the green leaves of NHE/TO had significantly lower levels of Mg and Ca compared to the green leaves of the LF/TO. This suggests that Mg deficiency may be the primary cause of chlorosis in NHE/TO. A greenhouse study using the same graft combinations showed that the LF/TO plants had better growth than the NHE/TO, possibly by promoting Mg uptake and/or improving Mg distribution to leaves, thereby increasing carbon dioxide (CO₂) assimilation and photosynthesis, optimizing carbohydrate distribution, and increasing plant biomass. This results in a phenotype that is tolerant to Mg deficiency. In conclusion, these findings suggest that the LF navel orange could be utilized in the development of new citrus varieties with improved Mg-use efficiency.

Remediation and characterization of emerging and environmental pollutants from residential wastewater using a nature-based system

The nature-based systems (NBS) are nature inspired, unflagging, efficient, and budget friendly ideas that evolved as ideal technologies for wastewater treatment. The present study deals with the purification of residential wastewater through the NBS, covering three seasons. The NBS embedded with the Canna lily effectively eliminated organic matter, nutrients, and heavy metals. Nearly 57.2-75.2% COD, 69.9-83.2% BOD, 73.4-90.6% TSS, 51.1-71.6% PO₄^3--P, 66.3-84.8% NH₄⁺-N, 52-61.5% NO₃^--N, and 68-70.6% NO₂^--N removal were achieved. Heavy metals like Al, Cr, Mn, Fe, Ni, Cu, Zn, Mo, and Pb were removed, with a 98.25% reduction in the total bacterial count. The pollutant removal's kinetics was calculated using first-order kinetics. The mass removal rate of BOD was high in monsoon (22.3 g/m²/d), and COD was high in summer (36.4 g/m²/d). Organic compound removal (65.2%), including emerging pollutants, was observed by gas chromatography-mass spectrometry (GCMS) analysis of water and Canna samples. Wavelength dispersive X-ray fluorescence spectrometer (WDXRF) studied the elements and oxides retention by media and accumulation by the plant. The CHN content of the Canna and its morphological study was checked using the carbon CHNS analyzer and scanning electron microscope-energy dispersive X-ray (SEM-EDX), respectively. The performance of the NBS was validated using variance, correlation, and principal component analysis (PCA). This study shows the NBS effects on the remediation of environmental and emerging contaminants from residential wastewater and further use it for horticultural activities, thereby achieving sustainable development goals.

Cation Composition Influences the Toxicity of Salinity to Freshwater Biota

The effects of salinization on freshwater ecosystems have been estimated by testing sodium chloride (NaCl) since it is the most widely used salt as a deicing agent and Na⁺ and Cl^- ions are the most representative in seawater composition. However, calcium, magnesium, and/or potassium are starting to be proposed as potential surrogates for NaCl, but for which ecotoxicological effects are less explored. This study aimed to identify (i) the less toxic salt to freshwater biota to be suggested as a safer alternative deicer and (ii) to contribute to the lower tiers of salinity risk assessment frameworks by identifying a more suitable surrogate salt than NaCl. The battery of ecotoxicity assays with five key trophic level species showed that among the tested salts (MgCl₂, CaCl₂, and KCl), KCl and CaCl₂ seemed to induce the highest and lowest toxicity, respectively, compared with NaCl. CaCl₂ is suggested as a safer alternative for use as a deicer and KCl as a surrogate for the risk assessment of seawater intrusion in coastal regions. These results enrich the salt toxicity database aiming to identify and propose more suitable surrogate salts to predict the effects of salinization to a broader extent.

Application of Magnesium and Calcium Sulfate on Growth and Physiology of Forage Crops under Long-Term Salinity Stress

Soil salinity is major threat to crop growth and reducing cultivated land areas and salt-resistant crops have been required to sustain agriculture in salinized areas. This original research was performed to determine the effectiveness of MgSO₄ (MS) and CaSO₄ (CS) for each species and assess changes in the physiology and growth of fodder crops after short and long-term salt stress. Six treatments (CON (control); NaCl (NaCl 100 mM); 1 MS (1 mM MgSO₄ + 100 mM NaCl); 2 MS (2 mM MgSO₄ + 100 mM NaCl); 7.5 CS (7.5 mM CaSO₄ + 100 mM NaCl); and 10 CS (10 mM CaSO₄ + 100 mM NaCl)) were applied to Red clover (Trifolium pratense) and Tall fescue (Festuca arundinacea) under greenhouse conditions. Cultivars were evaluated based on their dry weights, physiological parameters, forage quality, and ion concentrations. The biomass of both species decreased significantly under NaCl treatments and increased under the MS and CS treatments compared to solely salinity treatments. Salinity caused a decrease in the photosynthetic rate, but compared to CON, the MS and CS treatments yielded superior results. Moreover, the Na⁺/K⁺ ratio increased as Na⁺ concentration increased but crop quality (CP, NDF, ADF) did not show significant differences under salinity. Overall, we concluded that these T. pratense and F. arundinacea species demonstrated various responses to salinity, MS, and CS by different physiological and morphological parameters and it turned out to be efficient under salinity stress.

Leaf Nutritional Content, Tree Richness, and Season Shape the Caterpillar Functional Trait Composition Hosted by Trees

Nutritional content of host plants is expected to drive caterpillar species assemblages and their trait composition. These relationships are altered by tree richness-induced neighborhood variation and a seasonal decline in leaf quality. We tested how key functional traits related to the growth and defenses of the average caterpillar hosted by a tree species are shaped by nutritional host quality. We measured morphological traits and estimated plant community-level diet breadth based on occurrences from 1020 caterpillars representing 146 species in a subtropical tree diversity experiment from spring to autumn in one year. We focused on interspecific caterpillar trait variation by analyzing presence-only patterns of caterpillar species for each tree species. Our results show that tree richness positively affected caterpillar species-sharing among tree species, which resulted in lowered trait variation and led to higher caterpillar richness for each tree species. However, community-level diet breadth depended more on the nutritional content of host trees. Higher nutritional quality also supported species-poorer but more abundant communities of smaller and less well-defended caterpillars. This study demonstrates that the leaf nutritional quality of trees shapes caterpillar trait composition across diverse species assemblages at fine spatial scales in a way that can be predicted by ecological theory.

Effects of exogenous calcium on the drought response of the tea plant (Camellia sinensis (L.) Kuntze)

Background

Drought is one of the major factors reducing the yield of many crops worldwide, including the tea crop (Camellia sinensis (L.) Kuntze). Calcium participates in most of cellular signaling processes, and its important role in stress detection and triggering a response has been shown in many crops. The aim of this study was to evaluate possible effects of calcium on the tea plant response to drought.

Methods

Experiments were conducted using 3-year-old potted tea plants of the best local cultivar Kolkhida. Application of ammonium nitrate (control treatment) or calcium nitrate (Ca treatment) to the soil was performed before drought induction. Next, a 7-day drought was induced in both groups of plants. The following physiological parameters were measured: relative electrical conductivity, pH of cell sap, and concentrations of cations, sugars, and amino acids. In addition, relative expression levels of 40 stress-related and crop quality-related genes were analyzed.

Results

Under drought stress, leaf electrolyte leakage differed significantly, indicating greater damage to cell membranes in control plants than in Ca-treated plants. Calcium application resulted in greater pH of cell sap; higher accumulation of tyrosine, methionine, and valine; and a greater Mg²⁺ content as compared to control plants. Drought stress downregulated most of the quality-related genes in both groups of tea plants. By contrast, significant upregulation of some genes was observed, namely CRK45, NAC26, TPS11, LOX1, LOX6, Hydrolase22, DREB26, SWEET2, GS, ADC, DHN2, GOLS1, GOLS3, and RHL41. Among them, three genes (LOX1, RHL41, and GOLS1) showed 2-3 times greater expression in Ca-treated plants than in control plants. Based on these results, it can be speculated that calcium affects galactinol biosynthesis and participates in the regulation of stomatal aperture not only through activation of abscisic-acid signaling but also through jasmonic-acid pathway activation. These findings clarify calcium-mediated mechanisms of drought defense in tree crops. Thus, calcium improves the drought response in the tea tree.

Transcriptome Dynamics Underlying Magnesium Deficiency Stress in Three Founding Saccharum Species

Modern sugarcane cultivars were generated through interspecific crossing of the stress resistance Saccharum spontaneum and the high sugar content Saccharum officinarum which was domesticated from Saccharum robustum. Magnesium deficiency (MGD) is particularly prominent in tropical and subtropical regions where sugarcane is grown, but the response mechanism to MGD in sugarcane remains unknown. Physiological and transcriptomic analysis of the three founding Saccharum species under different magnesium (Mg) levels was performed. Our result showed that MGD decreased chlorophyll content and photosynthetic efficiency of three Saccharum species but led to increased starch in leaves and lignin content in roots of Saccharum robustum and Saccharum spontaneum. We identified 12,129, 11,306 and 12,178 differentially expressed genes (DEGs) of Saccharum officinarum, Saccharum robustum and Saccharum spontaneum, respectively. In Saccharum officinarum, MGD affected signal transduction by up-regulating the expression of xylan biosynthesis process-related genes. Saccharum robustum, responded to the MGD by regulating the expression of transcription and detoxification process-related genes. Saccharum spontaneum, avoids damage from MGD by regulating the expression of the signing transduction process and the transformation from growth and development to reproductive development. This novel repertoire of candidate genes related to MGD response in sugarcane will be helpful for engineering MGD tolerant varieties.

Coapplication of Effective Microorganisms and Nanomagnesium Boosts the Agronomic, Physio-Biochemical, Osmolytes, and Antioxidants Defenses Against Salt Stress in Ipomoea batatas

The application of bio- and nanofertilizers are undoubtedly opening new sustainable approaches toward enhancing abiotic stress tolerance in crops. In this study, we evaluated the application of effective microorganisms (EMs) of five groups belonging to photosynthetic bacteria, lactic acid bacteria, yeast, actinobacteria, and fermenting fungi combined with magnesium oxide (MgO) nanoparticles (MgO-NP) on the growth and productivity of sweet potato plants grown in salt-affected soils. In two field experiments carried out in 2020 and 2021, we tested the impacts of EMs using two treatments (with vs. without EMs as soil drench) coupled with three foliar applications of MgO-NP (0, 50, and 100 μg ml^–1 of MgO, representing MgO-NP₀, MgO-NP₅₀, and MgO-NP₁₀₀, respectively). In our efforts to investigate the EMs:MgO-NP effects, the performance (growth and yield), nutrient acquisition, and physio-biochemical attributes of sweet potatoes grown in salt-affected soil (7.56 dS m^–1) were assessed. Our results revealed that salinity stress significantly reduced the growth parameters, yield traits, photosynthetic pigment content (chlorophylls a and b, and carotenoids), cell membrane stability, relative water content, and nutrient acquisition of sweet potatoes. However, the EMs⁺ and/or MgO-NP-treated plants showed high tolerance to salt stress, specifically with a relatively superior increase when any of the biostimulants were combined. The application of EMs and/or MgO-NP improved osmotic stress tolerance by increasing the relative water content and membrane integrity. These positive responses owed to increase the osmolytes level (proline, free amino acids, and soluble sugars) and antioxidative compounds (non-enzymatic concentration, enzymatic activities, phenolic acid, and carotenoids). We also noticed that soil salinity significantly increased the Na⁺ content, whereas EMS⁺ and/or MgO-NP-treated plants exhibited lower Na⁺ concentration and increased K⁺ concentration and K⁺/Na⁺ ratio. These improvements contributed to increasing the photosynthetic pigments, growth, and yield under salinity stress. The integrative application of EMs and MgO-NP showed higher efficacy bypassing all single treatments. Our findings indicated the potential of coapplying EMs and MgO-NP for future use in attenuating salt-induced damage beneficially promoting crop performance.

Identification of Twelve Different Mineral Deficiencies in Hydroponically Grown Sunflower Plants on the Basis of Short Measurements of the Fluorescence and P700 Oxidation/Reduction Kinetics

The photosynthetic electron transport chain is mineral rich. Specific mineral deficiencies can modify the electron transport chain specifically. Here, it is shown that on the basis of 2 short Chl fluorescence and P700⁺ measurements (approx. 1 s each), it is possible to discriminate between 10 out of 12 different mineral deficiencies: B, Ca, Cu, Fe, K, Mg, Mn, Mo, N, P, S, and Zn. B- and Mo-deficient plants require somewhat longer measurements to detect the feedback inhibition they induce. Eight out of twelve deficiencies mainly affect PS I and NIR measurements are, therefore, very important for this analysis. In Cu- and P-deficient plants, electron flow from the plastoquinone pool to PS I, is affected. In the case of Cu-deficiency due to the loss of plastocyanin and in the case of P-deficiency probably due to a fast and strong generation of Photosynthetic Control. For several Ca-, K-, and Zn-deficient plant species, higher levels of reactive oxygen species have been measured in the literature. Here, it is shown that this not only leads to a loss of Pm (maximum P700 redox change) reflecting a lower PS I content, but also to much faster P700⁺ re-reduction kinetics during the I₂-P (~30-200 ms) fluorescence rise phase. The different mineral deficiencies affect the relation between the I₂-P and P700⁺ kinetics in different ways and this is used to discuss the nature of the relationship between these two parameters.

Suitability of Porous Inorganic Materials from Industrial Residues and Bioproducts for Use in Horticulture: A Multidisciplinary Approach

This study follows a circular economy approach through the preliminary implementation of a coated porous inorganic material (PIM), studied as sustainable controlled release fertilizer, and its application for lettuce Lactuca sativa L. cultivar Chiara growth. The PIM was made of pumice scraps that partially replaced clay as a natural raw material, spent coffee grounds as a porous agent, bovine bone ash and potassium carbonate to provide phosphorus (P) and potassium (K) nutrients, respectively. A coating made with defatted black soldier fly prepupae biomass was used as a nitrogen (N) source. Most of the ingredients used were industrial residues, with the aim of valorizing the raw waste materials present locally. The suitability of PIMs as a fertilizer was investigated with an interdisciplinary approach, which included the first chemical and physical characterization of the material, the evaluation of its antibacterial properties and of its use in horticulture through lettuce growth tests. As tests were carried out indoors, a specific LED lighting device was used to grow the lettuce. The release of nutrients into the soil was estimated by measuring the main elements in the fertilizers before and after their use in the soil. The first results from this characterization study support PIMs’ suitability for agronomic applications. The use of the PIMs suggested average higher dry weight (49%), fresh weight (112%), and leaf area (48%), compared to those with the use of a standard fertilizer soil, without the release of any dangerous element for the plant in the soil. These results are a promising beginning for the development of further studies already in progress on sustainable controlled-release fertilizers.

Four plasma membrane-localized MGR transporters mediate xylem Mg2+ loading for root-to-shoot Mg2+ translocation in Arabidopsis

Magnesium (Mg²⁺), an essential structural component of chlorophyll, is absorbed from the soil by roots and transported to shoots to support photosynthesis in plants. However, the molecular mechanisms underlying root-to-shoot Mg²⁺ translocation remain largely unknown. We describe here the identification of four plasma membrane (PM)-localized transporters, named Mg²⁺ release transporters (MGRs), that are critical for root-to-shoot Mg transport in Arabidopsis. Functional complementation assays in a Mg²⁺-uptake-deficient bacterial strain confirmed that these MGRs conduct Mg²⁺ transport. PM-localized MGRs (MGR4, MGR5, MGR6, and MGR7) were expressed primarily in root stellar cells and participated in the xylem loading step of the long-distance Mg²⁺ transport process. In particular, MGR4 and MGR6 played a major role in shoot Mg homeostasis, as their loss-of-function mutants were hypersensitive to low Mg²⁺ but tolerant to high Mg²⁺ conditions. Reciprocal grafting analysis further demonstrated that MGR4 functions in the root to determine shoot Mg²⁺ accumulation and physiological phenotypes caused by both low- and high-Mg²⁺ stress. Taken together, our study has identified the long-sought transporters responsible for root-to-shoot Mg²⁺ translocation in plants.

Physiological Essence of Magnesium in Plants and Its Widespread Deficiency in the Farming System of China

Magnesium (Mg) is an essential nutrient for a wide array of fundamental physiological and biochemical processes in plants. It largely involves chlorophyll synthesis, production, transportation, and utilization of photoassimilates, enzyme activation, and protein synthesis. As a multifaceted result of the introduction of high-yielding fertilizer-responsive cultivars, intensive cropping without replenishment of Mg, soil acidification, and exchangeable Mg (Ex-Mg) leaching, Mg has become a limiting nutrient for optimum crop production. However, little literature is available to better understand distinct responses of plants to Mg deficiency, the geographical distribution of soil Ex-Mg, and the degree of Mg deficiency. Here, we summarize the current state of knowledge of key plant responses to Mg availability and, as far as possible, highlight spatial Mg distribution and the magnitude of Mg deficiency in different cultivated regions of the world with a special focus on China. In particular, ~55% of arable lands in China are revealed Mg-deficient (< 120 mg kg-1 soil Ex-Mg), and Mg deficiency literally becomes increasingly severe from northern (227-488 mg kg-1) to southern (32-89 mg kg-1) China. Mg deficiency primarily traced back to higher depletion of soil Ex-Mg by fruits, vegetables, sugarcane, tubers, tea, and tobacco cultivated in tropical and subtropical climate zones. Further, each unit decline in soil pH from neutral reduced ~2-fold soil Ex-Mg. This article underscores the physiological importance of Mg, potential risks associated with Mg deficiency, and accordingly, to optimize fertilization strategies for higher crop productivity and better quality.

Magnesium absorption, translocation, subcellular distribution and chemical forms in citrus seedlings

Magnesium (Mg) is an essential macronutrient for plant growth and development; however, the adaptive mechanisms of Mg deficiency to underlying changes in Mg translocation, subcellular distribution and chemical forms in citrus plants are unknown. In this study, we conducted a sand culture experiment with 0 (Mg-deficiency) or 2 (Mg-sufficiency) mmol l-1 Mg2+ treatments to investigate the responses underlying Mg adaptability, as well as the resulting growth and Mg transport features in citrus seedlings [Citrus sinensis (L.) Osbeck cv. 'Xuegan']. We found that Mg-deficiency significantly depressed biomass by 39% in the whole plant and by 66% in branch organs compared with Mg-sufficient conditions, which further resulted in a subsequent decrease in Mg concentration and accumulation with changes in its distribution in different organs and a reduction in root growth. Under Mg-sufficiency, >50% of Mg was sequestered in the soluble fraction and this was reduced by 30% under Mg-deficiency. Furthermore, >70% of Mg existed as inorganic (42%) and water-soluble (31%) forms with high mobility across treatments and organs. Under Mg-deficiency, the proportion of water-soluble Mg was reduced in leaf and increased in root, whereas the proportion of inorganic Mg increased in main stem leaves and decreased in branch leaves and root. However, under Mg-deficiency, the proportion of Mg forms with low mobility, including pectates and proteins, phosphates, oxalates and residues, was increased in leaf and root organs, with the exception of pectate and protein Mg, which was decreased in root. The Mg transfer factor showed that Mg-deficiency improved Mg transport from parent to branch organs, which was related to Mg subcellular distribution and chemical forms. Taken together, our study establishes a defined process to clarify the mechanisms of Mg absorption and translocation and reveals a possible strategy to effectively improve Mg mobility and availability in citrus plants.

Star Polymers with Designed Reactive Oxygen Species Scavenging and Agent Delivery Functionality Promote Plant Stress Tolerance

Plant abiotic stress induces reactive oxygen species (ROS) accumulation in leaves that can decrease photosynthetic performance and crop yield. Materials that scavenge ROS and simultaneously provide nutrients in vivo are needed to manage this stress. Here, we incorporated both ROS scavenging and ROS triggered agent release functionality into an ∼20 nm ROS responsive star polymer (RSP) poly(acrylic acid)-block-poly((2-(methylsulfinyl)ethyl acrylate)-co-(2-(methylthio)ethyl acrylate)) (PAA-b-P(MSEA-co-MTEA)) that alleviated plant stress by simultaneous ROS scavenging and nutrient agent release. Hyperspectral imaging indicates that all of the RSP penetrates through the tomato leaf epidermis, and 32.7% of the applied RSP associates with chloroplasts in mesophyll. RSP scavenged up to 10 μmol mg^-1 ROS in vitro and suppressed ROS in vivo in stressed tomato (Solanum lycopersicum) leaves. Reaction of the RSP with H₂O₂in vitro enhanced the release of nutrient agent (Mg²⁺) from star polymers. Foliar applied RSP increased photosynthesis in plants under heat and light stress compared to untreated controls, enhancing the carbon assimilation, quantum yield of CO₂ assimilation, Rubisco carboxylation rate, and photosystem II quantum yield. Mg loaded RSP improved photosynthesis in Mg deficient plants, mainly by promoting Rubisco activity. These results indicate the potential of ROS scavenging nanocarriers like RSP to alleviate abiotic stress in crop plants, allowing crop plants to be more resilient to heat stress, and potentially other climate change induced abiotic stressors.

Below-ground plant-soil interactions affecting adaptations of rice to iron toxicity

Iron toxicity is a major constraint to rice production, particularly in highly weathered soils of inland valleys in sub-Saharan Africa where the rice growing area is rapidly expanding. There is a wide variation in tolerance of iron toxicity in the rice germplasm. However, the introgression of tolerance traits into high-yielding germplasm has been slow owing to the complexity of the tolerance mechanisms and large genotype-by-environment effects. We review current understanding of tolerance mechanisms, particularly those involving below-ground plant-soil interactions. Until now these have been less studied than above-ground mechanisms. We cover processes in the rhizosphere linked to exclusion of toxic ferrous iron by oxidation, and resulting effects on the mobility of nutrient ions. We also cover the molecular physiology of below-ground processes controlling iron retention in roots and root-shoot transport, and also plant iron sensing. We conclude that future breeding programmes should be based on well-characterized molecular markers for iron toxicity tolerance traits. To successfully identify such markers, the complex tolerance response should be broken down into its components based on understanding of tolerance mechanisms, and tailored screening methods should be developed for individual mechanisms.

Soil Sterilization Eliminates Beneficial Microbes That Provide Natural Pest Suppression Ecosystem Services Against Radopholus similis and Fusarium Oxysporum V5w2 in the Endosphere and Rhizosphere of Tissue Culture Banana Plants

Endosphere and rhizosphere microbes offer plant growth promotion and pest suppression ecosystem services in banana-based agroecosystems. Interest has been growing towards the use of such beneficial microbes in protecting vulnerable tissue culture banana plants against pathogens such as Radopholus similis and Fusarium oxysporum. A screenhouse experiment with potted tissue culture banana plants was conducted using sterile and non-sterile soil to investigate the effect of soil biota on R. similis and F. oxysporum strain V5w2. Plants grown in non-sterile soil had lower damage and R. similis density in roots and rhizosphere, while most plant growth-related parameters including root freshweight, shoot freshweight, total freshweight, plant height, and leaf size were larger compared to those from sterile soil. Shoot dryweight and Mg content were higher in plants from sterile soil, while their leaves developed discolored margins. R. similis-inoculated plants in sterile soil were smaller, had more dead roots, higher nematode density, and produced fewer and smaller leaves, than those from non-sterile soil. For all plant growth-related parameters, nematode density and root damage, no differences were recorded between controls and F. oxysporum V5w2-inoculated plants; and no differences between those inoculated with R. similis only and the ones co-inoculated with the nematode and F. oxysporum V5w2. Banana roots inoculated with F. oxysporum V5w2 were lighter in color than those without the fungus. Independent or combined inoculation of banana plants with F. oxysporum V5w2 and R. similis resulted in lower optical density of root extracts. In vitro assays indicated the presence of Fusarium spp. and other root endophytic microbes that interacted antagonistically with the inoculated strain of F. oxysporum V5w2. It is concluded that, soil sterilization eliminates beneficial microbes that provide natural pest suppression ecosystem services against R. similis and F. oxysporum in the endosphere and rhizosphere of tissue culture banana plants. I recommend the integration of microbiome conservation into tissue culture technology through the proposed “Tissue Culture Microbiome Conservation Technology.”

The Role of Plant Growth Promoting Rhizosphere Microbiome as Alternative Biofertilizer in Boosting Solanum melongena L. Adaptation to Salinity Stress

Recent ecological perturbations are presumed to be minimized by the application of biofertilizers as a safe alternative to chemical fertilizers. The current study aims to use bioinoculum (I) as an alternative biofertilizer and to alleviate salinity stress in the cultivar Solanum melongena L. Baldi. The salinity drench was 200 mM NaCl (S), which was used with different treatments (0; I; S; S + I) in pots prefilled with clay and sand (1:2). Results showed that salinity stress inhibited both plant fresh and dry weights, water content, and photosynthetic pigments. The content of root spermine (Spm), spermidine (Spd), and puterscine (Put) decreased. However, addition of the bioinoculum to salt-treated plants increased pigment content (80.35, 39.25, and 82.44% for chl a, chl b, and carotenoids, respectively). Similarly, K+, K+/Na+, Ca2+, P, and N contents were significantly enhanced. Increases were recorded for Spm + Spd and Put in root and shoot (8.4-F, 1.6-F and 2.04-F, 2.13-F, respectively). RAPD PCR showed gene expression upregulation of photosystem II D2 protein, glutathione reductase, glutathione-S-transferase, protease I, and protease II. The current work recommends application of the selected bioinoculum as a green biofertilizer and biopesticide. Additionally, the studied eggplant cultivar can be regarded as a source of salt tolerance genes in agricultural fields.

Inorganic Compounds that Aid in Obtaining Somatic Embryos

Somatic embryogenesis (SE) is a process that allows formation of embryos from somatic cells; this biological process has different stages that first require micropropagation and conditioning of explant, and then induction, multiplication, development, and germination of somatic embryos (SoE), to obtain seedlings that will be acclimatized and grown in a greenhouse to further be cultivated in the field. Inorganic compounds are supplemented by macro- and micronutrients that can conform different culture media, and with other compounds such as a carbon source, vitamins, and plant growth regulators (PGRs), will direct the fate of the plant cells to obtain SoE that will regenerate into plants. The concentration of these inorganic compounds must be optimized, since at very high concentrations they can cause toxicity and at low concentrations they may not induce the desired response. The objective of this chapter is to describe the most significant advances in the use of inorganic elements during the different stages of SE, starting with the description of the most used basal media and later describing the use of the main studied mineral elements during establishment of SE.

Deciphering the mechanism by which the yeast Phaffia rhodozyma responds adaptively to environmental, nutritional, and genetic cues

Phaffia rhodozyma is a basidiomycetous yeast that synthesizes astaxanthin (ASX), which is a powerful and highly valuable antioxidant carotenoid pigment. P. rhodozyma cells accrue ASX and gain an intense red-pink coloration when faced with stressful conditions such as nutrient limitations (e.g., nitrogen or copper), the presence of toxic substances (e.g., antimycin A), or are affected by mutations in the genes that are involved in nitrogen metabolism or respiration. Since cellular accrual of ASX occurs under a wide variety of conditions, this yeast represents a valuable model for studying the growth conditions that entail oxidative stress for yeast cells. Recently, we proposed that ASX synthesis can be largely induced by conditions that lead to reduction-oxidation (redox) imbalances, particularly the state of the NADH/NAD+ couple together with an oxidative environment. In this work, we review the multiple known conditions that elicit ASX synthesis expanding on the data that we formerly examined. When considered alongside the Mitchell's chemiosmotic hypothesis, the study served to rationalize the induction of ASX synthesis and other adaptive cellular processes under a much broader set of conditions. Our aim was to propose an underlying mechanism that explains how a broad range of divergent conditions converge to induce ASX synthesis in P. rhodozyma. The mechanism that links the induction of ASX synthesis with the occurrence of NADH/NAD+ imbalances may help in understanding how other organisms detect any of a broad array of stimuli or gene mutations, and then adaptively respond to activate numerous compensatory cellular processes.

Magnesium Limitation Leads to Transcriptional Down-Tuning of Auxin Synthesis, Transport, and Signaling in the Tomato Root

Magnesium (Mg) deficiency is becoming a widespread limiting factor for crop production. How crops adapt to Mg limitation remains largely unclear at the molecular level. Using hydroponic-cultured tomato seedlings, we found that total Mg2+ content significantly decreased by ∼80% under Mg limitation while K+ and Ca2+ concentrations increased. Phylogenetic analysis suggested that Mg transporters (MRS2/MGTs) constitute a previously uncharacterized 3-clade tree in planta with two rounds of asymmetric duplications, providing evolutionary evidence for further molecular investigation. In adaptation to internal Mg deficiency, the expression of six representative MGTs (two in the shoot and four in the root) was up-regulated in Mg-deficient plants. Contradictory to the transcriptional elevation of most of MGTs, Mg limitation resulted in the ∼50% smaller root system. Auxin concentrations particularly decreased by ∼23% in the Mg-deficient root, despite the enhanced accumulation of gibberellin, cytokinin, and ABA. In accordance with such auxin reduction was overall transcriptional down-regulation of thirteen genes controlling auxin biosynthesis (TAR/YUCs), transport (LAXs, PINs), and signaling (IAAs, ARFs). Together, systemic down-tuning of gene expression in the auxin signaling pathway under Mg limitation preconditions a smaller tomato root system, expectedly stimulating MGT transcription for Mg uptake or translocation.

Exploring the Effects of Magnesium Deficiency on the Quality Constituents of Hydroponic-Cultivated Tea (Camellia sinensis L.) Leaves

Magnesium (Mg) plays important roles in photosynthesis, sucrose partitioning, and biomass allocation in plants. However, the specific mechanisms of tea plant response to Mg deficiency remain unclear. In this study, we investigated the effects of Mg deficiency on the quality constituents of tea leaves. Our results showed that the short-term (7 days) Mg deficiency partially elevated the concentrations of polyphenols, free amino acids, and caffeine but decreased the contents of chlorophyll and Mg. However, long-term (30 days) Mg-deficient tea displayed decreased contents of these constituents. Particularly, Mg deficiency increased the index of catechins' bitter taste and the ratio of total polyphenols to total free amino acids. Moreover, the transcription of key genes involved in the biosynthesis of flavonoid, caffeine, and theanine was differentially affected by Mg deficiency. Additionally, short-term Mg deficiency induced global transcriptome change in tea leaves, in which a total of 2522 differentially expressed genes were identified involved in secondary metabolism, amino acid metabolism, and chlorophyll metabolism. These results may help to elucidate why short-term Mg deficiency partially improves the quality constituents of tea, while long-term Mg-deficient tea may taste more bitter, more astringent, and less umami.

Amending mine tailing cover with compost and biochar: effects on vegetation establishment and metal bioaccumulation in the Finnish subarctic

In the northern boreal zone, revegetation and landscaping of closed mine tailings are challenging due to the high concentrations of potentially toxic elements; the use of nutrient-poor, glacigenic cover material (till); cool temperatures; and short growing period. Recycled waste materials such as biochar (BC) and composted sewage sludge (CSS) have been suggested to improve soil forming process and revegetation success as well as decrease metal bioavailability in closed mine tailing areas. We conducted two field experiments in old iron mine tailings at Rautuvaara, northern Finland, where the native mine soil or transported cover till soil had not supported plant growth since the mining ended in 1989. The impacts of CSS and spruce (Picea abies)-derived BC application to till soil on the survival and growth of selected plant species (Pinus sylvestris, Salix myrsinifolia, and grass mixture containing Festuca rubra, Lolium perenne, and Trifolium repens) were investigated during two growing seasons. In addition, the potential of BC to reduce bioaccumulation of metals in plants was studied. We found that (1) organic amendment like CSS markedly enhanced the plant growth and is therefore needed for vegetation establishment in tailing sites that contained only transported till cover, and (2) BC application to till soil-CSS mixture further facilitated the success of grass mixtures resulting in 71-250% higher plant biomass. On the other hand, (3) no effects on P. sylvestris or S. myrsinifolia were recorded during the first growing seasons, and (4) accumulation of metals in cover plants was negligible and BC application to till further decreased the accumulation of Al, Cr, and Fe in the plant tissues.

Computer-Based Tools Unmask Critical Mineral Nutrient Interactions in Hoagland Solution for Healthy Kiwiberry Plant Acclimatization

The aim of this study was to better understand the response of ex vitro acclimatized plants grown to a set of mineral nutrient combinations based on Hoagland solution. To reach that, two computer-based tools were used: the design of experiments (DOE) and a hybrid artificial intelligence technology that combines artificial neural networks with fuzzy logic. DOE was employed to create a five-dimensional IV-design space by categorizing all macroelements and one microelement (copper) of Hoagland mineral solution, reducing the experimental design space from 243 (35) to 19 treatments. Typical growth parameters included hardening efficiency (Hard), newly formed shoot length (SL), total leaf number (TLN), leaf chlorophyll content (LCC), and leaf area (LA). Moreover, three physiological disorders, namely, leaf necrosis (LN), leaf spot (LS), and curled leaf (CL), were evaluated for each treatment (mineral formulation). All the growth parameters plus LN were successfully modeled using neuro-fuzzy logic with a high train set R 2 between experimental and predicted values (72.67 < R 2 < 98.79). The model deciphered new insights using different sets of "IF-THEN" rules, pinpointing the positive role of Mg2+ and Ca2+ to improve Hard, SL, TLN, and LA and alleviate LN but with opposite influences on LCC. On the contrary, TLN and LCC were negatively affected by the addition of NO3 - into the media, while NH4 + in complex interaction with Cu2+ or Mg2+ positively enhanced SL, TLN, LCC, and LA. In our opinion, the approach and results achieved in this work are extremely fruitful to understand the effect of Hoagland mineral nutrients on the healthy growth of ex vitro acclimatized plants, through identifying key factors, which favor growth and limit physiological abnormalities.

Genetic aluminium resistance coupled with foliar magnesium application enhances wheat growth in acidic soil

BACKGROUND

Soil acidity causes an increase in the solubility of toxic aluminium (Al), inhibiting root growth and limiting plant access to soil water and nutrients. Toxicity of Al decreases growth and development more in Al-sensitive than Al-resistant wheat (Triticum aestivum L.) genotypes. Applying magnesium (Mg) may alleviate Al toxicity in acidic soil. It is unclear if growing Al-resistant wheat, coupled with Mg application, will enhance wheat growth and physiological responses in acidic soil. Wheat was grown in the reconstituted acidic soil profile in a three-factor glasshouse experiment comprising foliar Mg at [Mg] = 0 and 200 mg L^-1 (using magnesium sulfate), wheat genotypes ES8 (Al sensitive) and ET8 (Al resistant), and four soil treatments [non-amended soil (pH_{0.1 M CaCl2}    4.0); 100% of the recommended lime dose in subsoil to raise pH to 6.0; or 20 mg Mg kg^-1 soil to the whole soil profile (as magnesium sulfate or magnesium chloride)].

RESULTS

Applying foliar Mg to Al-resistant wheat significantly increased shoot dry weight (24%), subsoil root dry weight (12%), subsoil coarse (>0.2 mm in diameter) root length (12%), net photosynthetic rate (28%), and total leaf area (10%) compared with plants not treated with foliar Mg. Combining foliar Mg application with subsoil liming increased the subsoil total root length by 1.3-fold compared with zero foliar Mg. Without foliar Mg, subsoil liming and soil Mg amendment significantly (by 10%) enhanced shoot growth and total leaf area compared with non-amended soil.

CONCLUSION

Growing an Al-resistant genotype coupled with applying Mg foliarly and to soil improved wheat growth in an acidic soil. © 2021 Society of Chemical Industry.

Linking Remotely Sensed Carbon and Water Use Efficiencies with In Situ Soil Properties

The capacity of terrestrial ecosystems to sequester carbon dioxide (CO2) from the atmosphere is expected to be altered by climate change and CO2 fertilization, but this projection is limited by our understanding of how the soil system interacts with plants. Understanding the soil–vegetation interactions is essential to assess the magnitude and response of terrestrial ecosystems to the changing climate. Here, we used soil profile and satellite data to explore the role that soil properties play in regulating water and carbon use by plants. Data obtained for 19 terrestrial ecosystem sites in a warm temperate and humid climate were used to investigate the relationship between remotely sensed data and soil physical and chemical properties. Classification and regression tree results showed that in situ soil carbon isotope (δ13C), and soil order were significant predictors (r2 = 0.39, mean absolute error (MAE) = 0 of 0.175 gC/KgH2O) of remotely sensed water use efficiency (WUE) based on the Moderate Resolution Imaging Spectroradiometer (MODIS). Soil extractable calcium (Ca), and land cover type were significant predictors of remotely sensed carbon use efficiency (CUE) based on MODIS and Landsat data-(r2 = 0.64–0.78, MAE = 0.04–0.06). We used gross primary productivity (GPP) derived from solar-induced fluorescence (SIF) data, based on the Orbiting Carbon Observatory-2 (OCO-2), to calculate WUE and CUE (referred to as WUESIF and CUESIF, respectively) for our study sites. The regression tree analysis revealed that soil organic matter and soil extractable magnesium (Mg), δ13C, and soil silt content were the important predictors of both WUESIF (r2 = 0.19, MAE = 0.64 gC/KgH2O) and CUESIF (r2 = 0.45, MAE = 0.1), respectively. Our results revealed the importance of soil extractable Ca, soil carbon (S13C is a facet of soil carbon content), and soil organic matter predicting CUE and WUE. Insights gained from this study highlighted the importance of biotic and abiotic factors regulating plant and soil interactions. These types of data are timely and critical for accurate predictions of how terrestrial ecosystems respond to climate change.

Differences in morphological and physiological features of citrus seedlings are related to Mg transport from the parent to branch organs

BACKGROUND

In this study, we aimed to test the hypothesis that magnesium (Mg) remobilization in citrus plants is regulated by Mg supply and contributes to differences in the growth of the parent and branch organs. Citrus seedlings were grown in sand under Mg deficient (0 mmol Mg²⁺ L^-1, -Mg) and Mg sufficient (2 mmol Mg²⁺ L^-1, + Mg) conditions. The effects on biomass, Mg uptake and transport, gas exchange and chlorophyll fluorescence, as well as related morphological and physiological parameters were evaluated in different organs.

RESULTS

Mg deficiency significantly decreased plant biomass, with a decrease in total plant biomass of 39.6%, and a greater than twofold decrease in the branch organs compared with that of the parent organs. Reduced photosynthesis capacity was caused by a decreased in pigment levels and photosynthetic electron transport chain disruption, thus affecting non-structural carbohydrate accumulation and plant growth. However, the adaptive responses of branch leaves to Mg deficiency were greater than those in parent leaves. Mg deficiency inhibited plant Mg uptake but enhanced Mg remobilization from parent to branch organs, thus changing related growth variables and physiological parameters, including protein synthesis and antioxidant enzyme activity. Moreover, in the principal components analysis, these variations were highly clustered in both the upper and lower parent leaves, but highly separated in branch leaves under the different Mg conditions.

CONCLUSIONS

Mg deficiency inhibits the growth of the parent and branch organs of citrus plants, with high Mg mobility contributing to differences in physiological metabolism. These findings suggest that Mg management should be optimized for sustainable citrus production.