Differential expression of molybdenum transport and assimilation genes between two winter wheat cultivars (Triticum aestivum)

Enrichment mechanisms of Mo in soil in the karst region Guangxi, China

Soils developed in karst regions have naturally high background values of molybdenum (Mo) due to geological factors. However, the enrichment mechanism of Mo in these soils are not fully understood, making it challenging to assess their ecological risk and utilize Mo-rich land resources. To shed light on this issue, this study collected and analyzed data from the 1:50,000 geochemical survey in Guangxi, including 536,503 sets of soil data and 3043 sets of rock data, as well as 40 sets of carbonate rock-soil from typical karst regions. The results showed that soil Mo enrichment is highly correlated with the distribution of carbonate rocks in karst regions. The carbonate rocks in these regions contain Mo ranging from 0.03 to 1.06 mg·kg^-1 (with a mean of 0.22 mg·kg^-1). In comparison, the soil Mo derived from carbonate rocks can reach up to 6.00 mg·kg^-1 (with a mean of 2.75 mg·kg^-1), representing an average enrichment of soil Mo that is 24 times higher compared to the carbonate parent rock. The enrichment of soil Mo in karst regions is primarily controlled by secondary enrichment during the weathering process of carbonate. During the insoluble residue accumulation process, the dissolution of carbonate leads to a dramatic reduction in bedrock volume, and the adsorption of clay minerals and Fe minerals in insoluble residues plays an essential role in Mo enrichment during these stages. During the soil-forming stage of the insoluble residue, most Mo leaches into the water body due to the mineral transformation of insoluble residue. Consequently, as Fe-Mn nodules in soils become more enriched with increasing weathering intensity, some Mo is absorbed and passivated by iron and manganese oxides (hydroxides). Accordingly, the contribution of Fe-Mn nodules and the degree of leaching were closely related to the enrichment of soil Mo in karst regions. This study provides insights into the enrichment mechanisms of Mo in soils developed in karst regions, which will help to evaluate their ecological risk in these environments.

Interaction between selenium and essential micronutrient elements in plants: A systematic review

Nutrient imbalance (i.e., deficiency and toxicity) of microelements is an outstanding environmental issue that influences each aspect of ecosystems. Although the crucial roles of microelements in entire lifecycle of plants have been widely acknowledged, the effective control of microelements is still neglected due to the narrow safe margins. Selenium (Se) is an essential element for humans and animals. Although it is not believed to be indispensable for plants, many literatures have reported the significance of Se in terms of the uptake, accumulation, and detoxification of essential microelements in plants. However, most papers only concerned on the antagonistic effect of Se on metal elements in plants and ignored the underlying mechanisms. There is still a lack of systematic review articles to summarize the comprehensive knowledge on the connections between Se and microelements in plants. In this review, we conclude the bidirectional effects of Se on micronutrients in plants, including iron, zinc, copper, manganese, nickel, molybdenum, sodium, chlorine, and boron. The regulatory mechanisms of Se on these micronutrients are also analyzed. Moreover, we further emphasize the role of Se in alleviating element toxicity and adjusting the concentration of micronutrients in plants by altering the soil conditions (e.g., adsorption, pH, and organic matter), promoting microbial activity, participating in vital physiological and metabolic processes, generating element competition, stimulating metal chelation, organelle compartmentalization, and sequestration, improving the antioxidant defense system, and controlling related genes involved in transportation and tolerance. Based on the current understanding of the interaction between Se and these essential elements, future directions for research are suggested.

Genome-Wide Association Study Reveals Genomic Regions Associated With Molybdenum Accumulation in Wheat Grains

Molybdenum (Mo) is an essential micronutrient for almost all organisms. Wheat, a major staple crop worldwide, is one of the main dietary sources of Mo. However, the genetic basis for the variation of Mo content in wheat grains remains largely unknown. Here, a genome-wide association study (GWAS) was performed on the Mo concentration in the grains of 207 wheat accessions to dissect the genetic basis of Mo accumulation in wheat grains. As a result, 77 SNPs were found to be significantly associated with Mo concentration in wheat grains, among which 52 were detected in at least two sets of data and distributed on chromosome 2A, 7B, and 7D. Moreover, 48 out of the 52 common SNPs were distributed in the 726,761,412-728,132,521 bp genomic region of chromosome 2A. Three putative candidate genes, including molybdate transporter 1;2 (TraesCS2A02G496200), molybdate transporter 1;1 (TraesCS2A02G496700), and molybdopterin biosynthesis protein CNX1 (TraesCS2A02G497200), were identified in this region. These findings provide new insights into the genetic basis for Mo accumulation in wheat grains and important information for further functional characterization and breeding to improve wheat grain quality.

Molybdenum-induced endogenous nitric oxide (NO) signaling coordinately enhances resilience through chlorophyll metabolism, osmolyte accumulation and antioxidant system in arsenate stressed-wheat (Triticum aestivum L.) seedlings

There is little information available to decipher the interaction between molybdenum (Mo) and nitric oxide (NO) in mitigating arsenic (As^V) stress in plants. The present work highlights the associative role of exogenous Mo and endogenous NO signaling in regulating As^V tolerance in wheat seedlings. Application of Mo (1 μM) on 25-day-old wheat seedlings grown in the presence (5 μM) or absence of As^V stress caused improvement of photosynthetic pigment metabolism, reduction of electrolytic leakage and reactive oxygen species (ROS), and higher accumulation of osmolytes (proline and total soluble sugars). The molybdenum treatment upregulated antioxidative enzymes, such as superoxide dismutase, ascorbate peroxidase and glutathione reductase. In addition, the accumulation of nonenzymatic antioxidants (ascorbate and glutathione) was correlated with an increase in ascorbate peroxidase and glutathione reductase activity. The application of cPTIO (endogenous NO scavenger; 100 μM) reversed the Mo-mediated effects, thus indicating that endogenous NO may accompany Mo-induced mitigation of As^V stress. Mo treatment stimulated the accumulation of endogenous NO in the presence of As^V stress. Thus, it is evident that Mo and NO-mediated As^V stress tolerance in wheat seedlings are primarily operative through chlorophyll restoration, osmolytes accumulation, reduced electrolytic leakage, and ROS homeostasis.

Comparison of foliar spray and soil irrigation of biogenic CuO nanoparticles (NPs) on elemental uptake and accumulation in lettuce

Nanoparticles (NPs) can be used in several ways in agriculture, including increasing production rates and improving nutritional values in plants. The present study aims to clarify how biogenic copper oxide nanoparticles (CuO NPs) applied by two routes of exposure (foliar spray and soil irrigation) affect the elemental uptake by lettuce. In vivo experiments using lettuce (n = 4) were performed with CuO NPs in comparison with copper salt (CuSO4), considering a final mass added of 20 mg of CuO per plant. The elemental composition of roots was mostly affected by the soil irrigation exposure for both Cu forms (NPs and salt). Neither Cu form added by soil irrigation was translocated to leaves. Copper concentration in leaves was mainly affected by foliar spray exposure for both Cu forms (NPs and salt). All Cu forms through foliar spray were sequestered in the leaves and no translocation to roots was observed. Foliar spray of CuO NPs caused no visual damage in leaves, resulted in less disturbance of elemental composition, and improved dry weight, number of leaves, CO2 assimilation, and the levels of K, Na, S, Ag, Cd, Cr, Cu, and Zn in leaves without causing significant changes in daily intake of most elements, except for Cu. Although Cu concentration increased in leaves by foliar spray of CuO NPs, it remained safe for consumption.

Molybdenum-induced effects on photosynthetic efficacy of winter wheat (Triticum aestivum L.) under different nitrogen sources are associated with nitrogen assimilation

Different nitrogen (N) sources have been reported to significantly affect the photosynthesis (P_n) and its attributes. However, molybdenum (Mo) induced effects on photosynthetic efficacy of winter wheat under different N sources have not been investigated. A hydroponic study was carried out comprising of two winter wheat cultivars '97003' and '97014' as Mo-efficient and Mo-inefficient, respectively to underpin the effects of Mo supply (0 and 1 μM) on photosynthetic efficacy of winter wheat under different N sources (NO₃^̶, NH₄NO₃ or NH₄⁺). The results revealed that Mo-induced increases in dry weight, gas exchange parameters, chlorophyll contents, NR activities, NO₃^̶ assimilation, total N contents and transcripts of TaNR and TaNRT1.1 genes under different N sources followed the trend of NH₄NO₃ > NO₃^̶ > NH₄⁺, suggesting that Mo has more complementary effects to nitrate nutrition than sole ammonium. Interestingly, under Mo-deprivation environments, cultivar '97003' recorded more pronounced alterations in Mo-dependent parameters than '97014' cultivar. Moreover, Mo application significantly improved the chlorophyll contents and chloroplast configuration in all N sources showing that Mo has a key role in chlorophyll biosynthesis and chloroplast integrity. The results also highlighted that Mo-induced enhancements in total N contents and photosynthetic characteristics followed the same order as NH₄NO₃ > NO₃^- > NH₄⁺, suggesting that Mo might affect P_n through N metabolism. In crux, our study findings imply that Mo supply increased P_n not only through chlorophyll synthesis and chloroplast configuration but also by N uptake and assimilation which may represent a strategy of Mo fertilizer to strengthen the photosynthetic machinery.

Molybdenum-Induced Effects on Nitrogen Metabolism Enzymes and Elemental Profile of Winter Wheat (Triticum aestivum L.) Under Different Nitrogen Sources

Different nitrogen (N) sources have been reported to significantly affect the activities and expressions of N metabolism enzymes and mineral elements concentrations in crop plants. However, molybdenum-induced effects in winter wheat cultivars have still not been investigated under different N sources. Here, a hydroponic study was carried out to investigate these effects on two winter wheat cultivars (‘97003’ and ‘97014’) as Mo-efficient and Mo-inefficient, respectively, under different N sources (NO₃⁻, NH₄NO₃, and NH₄⁺). The results revealed that the activities of nitrate reductase (NR) and nitrite reductase (NiR) followed the order of NH₄NO₃ > NO₃⁻ > NH₄⁺ sources, while glutamine synthetase (GS) and glutamate synthase (GOGAT) followed the order of NH₄⁺ > NH₄NO₃ > NO₃⁻ in both the wheat cultivars. However, Mo-induced effects in the activities and expressions of N metabolism enzymes under different N sources followed the order of NH₄NO₃ > NO₃⁻ > NH₄⁺ sources, indicating that Mo has more complementary effects towards nitrate nutrition than the sole ammonium source in winter wheat. Interestingly, under −Mo-deprived conditions, cultivar ‘97003’ recorded more pronounced alterations in Mo-dependent parameters than ‘97014’ cultivar. Moreover, Mo application increased the proteins, amino acids, ammonium, and nitrite contents while concomitantly decreasing the nitrate contents in the same order of NH₄NO₃ > NO₃⁻ > NH₄⁺ sources that coincides with the Mo-induced N enzymes activities and expressions. The findings of the present study indicated that Mo plays a key role in regulating the N metabolism enzymes and assimilatory products under all the three N sources; however, the extent of complementation exists in the order of NH₄NO₃ > NO₃⁻ > NH₄⁺ sources in winter wheat. In addition, it was revealed that mineral elements profiles were mainly affected by different N sources, while Mo application generally had no significant effects on the mineral elements contents in the winter wheat leaves under different N sources.

Absorption Kinetics and Subcellular Fractionation of Zinc in Winter Wheat in Response to Nitrogen Supply

Nitrogen (N) is critical for zinc (Zn) absorption into plant roots; this in turn allows for Zn accumulation and biofortification of grain in winter wheat (Triticum aestivum L.), an important food crop. However, little is known about root morphology and subcellular Zn distribution in response to N treatment at different levels of Zn supply. In this study, two nutrient solution culture experiments were conducted to examine Zn accumulation, Zn absorption kinetics, root morphology, and Zn subcellular distribution in wheat seedlings pre-cultured with different N concentrations. The results showed positive correlations between N and Zn concentrations, and N and Zn accumulation, respectively. The findings suggested that an increase in N supply enhanced root absorption and the root-to-shoot transport of Zn. Nitrogen combined with the high Zn (Zn10) treatment increased the Zn concentration and consequently its accumulation in both shoots and roots. The maximum influx rate (Vmax), root length, surface area, and volume of 14-d-old seedlings, and root growth from 7 to 14 d in the medium N (N7.5) treatment were higher, but the Michaelis constant (Km) and minimum equilibrium concentrations (Cmin) in this treatment were lower than those in the low (N0.05) and high (N15) N treatments, when Zn was supplied at a high level (Zn10). Meanwhile, there were no pronounced differences in the above root traits between the N0.05Zn0 and N7.5Zn10 treatments. An increase in N supply decreased Zn in cell walls and cell organelles, while it increased Zn in the root soluble fraction. In leaves, an increase in N supply significantly decreased Zn in cell walls and the soluble fraction, while it increased Zn in cell organelles under Zn deficiency, but increased Zn distribution in the soluble fraction under medium and high Zn treatments. Therefore, a combination of medium N and high Zn treatments enhanced Zn absorption, apparently by enhancing Zn membrane transport and stimulating root development in winter wheat. An increase in N supply was beneficial in terms of achieving a balanced distribution of Zn subcellular fractions, thus enhancing Zn translocation to shoots, while maintaining normal metabolism.

Comparison of the effects of commercial coated and uncoated ZnO nanomaterials and Zn compounds in kidney bean (Phaseolus vulgaris) plants

Bean (Phaseolus vulgaris) plants were grown for 45 days in soil amended with either uncoated (Z-COTE^®) and coated (Z-COTE HP1^®) ZnO nanomaterials (NMs), bulk ZnO and ZnCl₂, at 0-500mg/kg. At harvest, growth parameters, chlorophyll, and essential elements were determined. None of the treatments affected germination and pod production, and only ZnCl₂ at 250 and 500mg/kg reduced relative chlorophyll content by 34% and 46%, respectively. While Z-COTE^® did not produce phenotypic changes, Z-COTE HP1^®, at all concentrations, increased root length (∼44%) and leaf length (∼13%) compared with control. Bulk ZnO reduced root length (53%) at 62.5mg/kg and ZnCl₂ reduced leaf length (16%) at 125mg/kg. Z-COTE^®, at 125mg/kg, increased Zn by 203%, 139%, and 76% in nodules, stems, and leaves, respectively; while at the same concentration, Z-COTE HP1^® increased Zn by 89%, 97%, and 103% in roots, stems, and leaves, respectively. At 125mg/kg, Z-COTE HP1^® increased root S (65%) and Mg (65%), while Z-COTE^® increased stem B (122%) and Mn (73%). Bulk ZnO and ZnCl₂ imposed more toxicity to kidney bean than the NMs, since they reduced root and leaf elongation, respectively, and the concentration of several essential elements in tissues.

Uptake, transport and distribution of molybdenum in two oilseed rape (Brassica napus L.) cultivars under different nitrate/ammonium ratios

OBJECTIVES

To investigate the effects of different nitrate sources on the uptake, transport, and distribution of molybdenum (Mo) between two oilseed rape (Brassica napus L.) cultivars, L0917 and ZS11.

METHODS

A hydroponic culture experiment was conducted with four nitrate/ammonium (NO₃^-:NH₄⁺) ratios (14:1, 9:6, 7.5:7.5, and 1:14) at a constant nitrogen concentration of 15 mmol/L. We examined Mo concentrations in roots, shoots, xylem and phloem sap, and subcellular fractions of leaves to contrast Mo uptake, transport, and subcellular distribution between ZS11 and L0917.

RESULTS

Both the cultivars showed maximum biomass and Mo accumulation at the 7.5:7.5 ratio of NO₃^-:NH₄⁺ while those were decreased by the 14:1 and 1:14 treatments. However, the percentages of root Mo (14.8% and 15.0% for L0917 and ZS11, respectively) were low under the 7.5:7.5 treatment, suggesting that the equal NO₃^-:NH₄⁺ ratio promoted Mo transportation from root to shoot. The xylem sap Mo concentration and phloem sap Mo accumulation of L0917 were lower than those of ZS11 under the 1:14 treatment, which suggests that higher NO₃^-:NH₄⁺ ratio was more beneficial for L0917. On the contrary, a lower NO₃^-:NH₄⁺ ratio was more beneficial for ZS11 to transport and remobilize Mo. Furthermore, the Mo concentrations of both the cultivars' leaf organelles were increased but the Mo accumulations of the cell wall and soluble fraction were reduced significantly under the 14:1 treatment, meaning that more Mo was accumulated in organelles under the highest NO₃^-:NH₄⁺ ratio.

CONCLUSIONS

This investigation demonstrated that the capacities of Mo absorption, transportation and subcellular distribution play an important role in genotype-dependent differences in Mo accumulation under low or high NO₃^-:NH₄⁺ ratio conditions.

Effect of exogenously applied molybdenum on its absorption and nitrate metabolism in strawberry seedlings

Molybdenum (Mo)-an essential element of plants-is involved in nitrogen (N) metabolism. Plants tend to accumulate more nitrate and show lower nitrogen use efficiency (NUE) under Mo-deficient conditions. Improving NUE in fruits reduces the negative effect of large applications of chemical fertilizer, but the mechanisms underlying how Mo enhances NUE remain unclear. We cultivated strawberry seedlings sprayed with 0, 67.5, 135, 168.75, or 202.5 g Mo·ha^-1 in a non-soil culture system. The Mo concentration in every plant tissue analyzed increased gradually as Mo application level rose. Mo application affected iron, copper, and selenium adsorption in roots. Seedlings sprayed with 135 g Mo·ha^-1 had a higher [¹⁵N] shoot:root (S:R) ratio, and ¹⁵NUE, and produced higher molybdate transporter type 1 (MOT1) expression levels in the roots and leaves. Seedlings sprayed with 135 g Mo·ha^-1 also had relatively high nitrogen metabolic enzyme activities and up-regulated transcript levels of nitrate uptake genes (NRT1.1; NRT2.1) and nitrate-responsive genes. Furthermore, there was a significantly lower NO₃^- concentration in the leaves and roots, a higher NH₄⁺ concentration in leaves, and a higher glutamine/glutamate (Gln/Glu) concentration at 135 g Mo·ha^-1. Seedlings sprayed with 202.5 g Mo·ha^-1 showed the opposite trend. Taken together, these results suggest that a 135 g Mo·ha^-1 application was optimal because it enhanced NO₃^- transport from the roots to the shoots and increased NUE by mediating nitrogen metabolic enzyme activities, nitrate transport, and nitrate assimilation gene activities.

Effects of tungsten on uptake, transport and subcellular distribution of molybdenum in oilseed rape at two different molybdenum levels

Due to the similarities of molybdenum (Mo) with tungsten (W) in the physical structure and chemical properties, studies involving the two elements have mainly examined their competitive relationships. The objectives of this study were to assess the effects of equimolar W on Mo accumulation, transport and subcellular distribution in oilseed rape at two Mo levels with four treatments: Mo₁ (1μmol/L Mo, Low Mo), Mo₁+W₁ (1μmol/L Mo+1μmol/LW, Low Mo with Low W), Mo₂₀₀ (200μmol/L Mo, High Mo) and Mo₂₀₀+W₂₀₀ (200μmol/L Mo+200μmol/L Mo, High Mo with high W). The fresh weight and root growth were inhibited by equimolar W at both low and high Mo levels. The Mo concentration and accumulation in root was increased by equimolar W at the low Mo level, but that in the root and shoot was decreased at the high Mo level. Additionally, equimolar W increased the Mo concentrations of xylem and phloem sap at low Mo level, but decreased that of xylem and increased that of phloem sap at the high Mo level. Furthermore, equimolar W decreased the expression of BnMOT1 in roots and leaves at the low Mo level, and only decreased its expression in leaves at the high Mo level. The expression of BnMOT2 was also decreased in root for equimolar W compared with the low Mo level, but increased compared with high Mo level. Moreover, equimolar W increased the proportion of Mo in cell wall fraction in root and that of soluble fraction in leaves when compared with the low Mo level. The results suggest that cell wall and soluble fractions might be responsible for the adaptation of oilseed rape to W stress.

Aided phytostabilization of a trace element-contaminated technosol developed on steel mill wastes

Aided phytostabilization of a barren, alkaline metal(loid)-contaminated technosol developed on steel mill wastes, with high soluble Cr and Mo concentrations, was assessed in a pot experiment using (1) Ni/Cd-tolerant populations of Festuca pratensis Huds., Holcus lanatus L., and Plantago lanceolata L. sowed in mixed stand and (2) six soil treatments: untreated soil (UNT), ramial chipped wood (RCW, 500m³ha^-1), composted sewage sludge (CSS, 120t DW ha^-1), UNT soil amended with compost (5% w/w) and either vermiculite (5%, VOM) or iron grit (1%, OMZ), and an uncontaminated soil (CTRL). In the CSS soil, pH and soluble Cr decreased whereas soluble Cu, K, Fe, Mn, Mg, Ni and P increased. The RCW treatment enhanced soluble Fe, Mn, and Mg concentrations. After 15 weeks, shoot DW yield and shoot Cd, Cu, Fe, Mn, Mo, Zn, and Mg removals peaked for F. pratensis grown on the CSS soil, with lowest shoot Cr, Ni and Mo concentrations. Holcus lanatus only grew on the CTRL, UNT, and CSS soils and P. lanceolata on the CTRL soil. Best treatment, F. pratensis grown on the CSS soil, led to a dense grass cover but its shoot Mo concentration exceeded the maximum permitted concentration in forage.

Foliar applied nanoscale and microscale CeO2 and CuO alter cucumber (Cucumis sativus) fruit quality

There is lack of information about the effects of foliar applied nanoparticles on fruit quality. In this study, three week-old soil grown cucumber seedlings were foliar-exposed to nCeO2, nCuO, and corresponding bulk counterparts at 50, 100, and 200mg/L. Respective suspensions/solutions were sprayed to experimental units in a volume of 250ml. Net photosynthesis rate (Pn), stomatal conductance (Gs), and transpiration rate (E) were measured 15days after treatment application and in 74day-old plants. Yield, fruit characteristics (size, weight, and firmness), Ce, Cu, and nutritional elements were also measured. Results showed a nano-specific decrement on Pn (22% and 30%) and E (11% and 17%) in seedling leaves exposed to nCeO2 and nCuO at 200mg/L, respectively, compared with control. nCeO2 at 50mg/L, bCeO2 at 200mg/L, and all Cu treatments, except nCuO at 100mg/L, significantly reduced fruit firmness (p≤0.05), compared with control. However, nCuO at 200mg/L and bCuO at 50mg/L significantly increased fruit fresh weight (p≤0.05). At 200mg/L, nCeO2 and bCeO2 reduced fruit Zn by 25%, while nCuO and bCuO reduced fruit Mo by 51% and 44%, respectively, compared with control. This study has shown that when the route of exposure is the foliage, differences in particle size are less significant, compared to root-based exposure. To the authors' knowledge, this is the first report on the effect of foliar application of nCeO2 and nCuO upon yield and nutritional quality of cucumber.

Physiological and Molecular Aspects of Tolerance to Environmental Constraints in Grain and Forage Legumes

Despite the agronomical and environmental advantages of the cultivation of legumes, their production is limited by various environmental constraints such as water or nutrient limitation, frost or heat stress and soil salinity, which may be the result of pedoclimatic conditions, intensive use of agricultural lands, decline in soil fertility and environmental degradation. The development of more sustainable agroecosystems that are resilient to environmental constraints will therefore require better understanding of the key mechanisms underlying plant tolerance to abiotic constraints. This review provides highlights of legume tolerance to abiotic constraints with a focus on soil nutrient deficiencies, drought, and salinity. More specifically, recent advances in the physiological and molecular levels of the adaptation of grain and forage legumes to abiotic constraints are discussed. Such adaptation involves complex multigene controlled-traits which also involve multiple sub-traits that are likely regulated under the control of a number of candidate genes. This multi-genetic control of tolerance traits might also be multifunctional, with extended action in response to a number of abiotic constraints. Thus, concrete efforts are required to breed for multifunctional candidate genes in order to boost plant stability under various abiotic constraints.