Root-shoot-root Fe translocation in cucumber plants grown in a heterogeneous Fe provision

Occurrence and transformation of heavy metals during swine waste treatment: A full scale study

This study tracked the fate of nine detected heavy metals in an industrial swine farm with integrated waste treatment, including anoxic stabilization, fixed-film anaerobic digestion, anoxic-oxic (A/O), and composting. Results show that heavy metals exhibited different transformation behaviors in the treatment streamline with Fe, Zn, Cu and Mn as the most abundant ones in raw swine waste. The overall removal of water-soluble heavy metals averaged at 30 %, 24 % and 42 % by anoxic stabilization, anaerobic digestion and A/O unit, respectively. In particular, anoxic stabilization could effectively remove Cu, Mn and Ni; while A/O unit was highly effective for Fe, Cr and Zn elimination from water-soluble states. As such, the environmental risk of liquid products for agricultural irrigation decreased gradually to the safe pollution level in swine waste treatment. Furthermore, heavy metals in the solid (slurry) phase of these bioprocesses could be immobilized with the passivation rate in the range of 42-70 %. Nevertheless, heavy metals preferably transformed from liquid to biosolids to remain their environmental risks when biosolids were used as organic fertilizer in agriculture, thereby requiring effective strategies to advance their passivation in all bioprocesses, particularly composting as the last treatment unit.

Iron (Fe) toxicity, uptake, translocation, and physio-morphological responses in Catharanthus roseus

Iron (Fe) toxicity in plant species depends on the availability of Fe in the soil, uptake ability by the root system, and translocation rate to other parts of the plant. The aim of this study was to assess Fe uptake by root tissues of Catharanthus roseus, translocation rate to leaf tissues, and the impairment of plant physio-morphological characteristics. Fe uptake by the roots (~ 700 µg g-1 DW) of C. roseus was observed during the early exposure period (1 week), and translocation factor from root to shoot was fluctuated as an independent strategy. A high level of Fe content in the root tissues significantly inhibited root length and root dry weight. Under acidic pH condition, an enrichment of Fe in the shoots (~ 400 µg g-1 DW) led to increase in leaf temperature (> 2.5 °C compared to control) and crop stress index (> 0.6), resulting in stomatal closure, subsequently decreasing CO2 assimilation rate and H2O transpiration rate. An increment of CSI in Fe-stressed plants was negatively related to stomatal conductance, indicating stomatal closure with an increase in Fe in the leaf tissues. High Fe levels in the leaf tissues directly induced toxic symptoms including leaf bronzing, leaf spotting, leaf necrosis, leaf chlorosis, and leaf senescence in C. roseus plants. In summary, C. roseus was identified as a good candidate plant for Fe phytoextraction, depending on Fe bioaccumulation, therefore 50 mM Fe treatment was designated as an excess Fe to cause the growth inhibition, especially in the prolonged Fe incubation periods.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01379-5.

Coated Hematite Nanoparticles Alleviate Iron Deficiency in Cucumber in Acidic Nutrient Solution and as Foliar Spray

Micronutrient iron (Fe) deficiency poses a widespread agricultural challenge with global implications. Fe deficiency affects plant growth and immune function, leading to reduced yields and contributing to the global "hidden hunger." While conventional Fe-based fertilizers are available, their efficacy is limited under certain conditions. Most recently, nanofertilizers have been shown as promising alternatives to conventional fertilizers. In this study, three nanohematite/nanoferrihydrite preparations (NHs) with different coatings were applied through the roots and shoots to Fe-deficient cucumber plants. To enhance Fe mobilization to leaves during foliar treatment, the plants were pre-treated with various acids (citric acid, ascorbic acid, and glycine) at a concentration of 0.5 mM. Multiple physiological parameters were examined, revealing that both root and foliar treatments resulted in improved chlorophyll content, biomass, photosynthetic parameters, and reduced ferric chelate reductase activity. The plants also significantly accumulated Fe in their developing leaves and its distribution after NHs treatment, detected by X-ray fluorescence mapping, implied long-distance mobilization in their veins. These findings suggest that the applied NHs effectively mitigated Fe deficiency in cucumber plants through both modes of application, highlighting their potential as nanofertilizers on a larger scale.

Combining micro- and portable-XRF as a tool for fast identification of virus infections in plants: The case study of ASa-Virus in Fraxinus ornus L

Plant viruses can affect micro- and macro-nutrients homeostasis in woody plants, with fluctuation in the concentration of some elements at the leaf level due to the pathogen activity and/or the plant physiological response to the infection.Leaves of Fraxinus ornus L. (flowering ash) were sampled for three consecutive years in the city of Hamburg (Germany), from both trees showing the typical symptoms of the ash shoestring associated virus infection (ASaV+) and healthy trees (ASaV-). Such leaves were analyzed by μ-XRF, using both laboratory and synchrotron X-ray sources, and large differences between symptomatic and not symptomatic leaves were observed: ASaV+ samples showed uneven element distribution and regions of the lamina with severe depletions of P, S, and Ca. Differently, K appeared more concentrated. Thus, 139 leaflets sampled from various healthy and infected ash trees over the three-year period were analyzed for K and Ca concentration with a portable XRF instrument. We found that the K:Ca concentration ratio was always significantly higher in ASaV+ samples, and this trend was verified for all the samplings over the tree years. We conclude that the K:Ca ratio parameter has potential in the frame of trendsetting diagnostics and could be used, together with visual symptoms, for a rapid, non-destructive, on-site and cheap indirect ASaV detection.

Brassinolide alleviates Fe deficiency-induced stress by regulating the Fe absorption mechanism in Malus hupehensis Rehd

Exogenous brassinolide promotes Fe absorption through mechanism I strategy, thus improving the tolerance of Malus hupehensis seedlings to Fe deficiency stress. Iron (Fe) deficiency is a common nutritional disorder that results in decreased yield and poor fruit quality in apple production. As a highly active synthetic analog of brassinosteroids, brassinolide (BL) plays numerous roles in plant responses to abiotic stresses. However, its role in Fe deficiency stress in apple plants has never been reported. Herein, we found that the exogenous application of 0.2 mg L^-1 BL could significantly enhance the tolerance of apple seedlings to Fe deficiency stress and result in a low etiolation rate and a high photosynthetic rate. The functional mechanisms of this effect were also explored. We found that first, exogenous BL could improve Fe absorption through the mechanism I strategy. BL induced the activity of H⁺-ATPase and the expression of MhAHA family genes, resulting in rhizosphere acidification. Moreover, BL could enhance the activity of Fe chelate reductase and absorb Fe through direct binding with the E-box of the MhIRT1 or MhFRO2 promoter via the transcription factors MhBZR1 and MhBZR2. Second, exogenous BL alleviated osmotic stress by increasing the contents of osmolytes (proline, solution proteins, and solution sugar) and scavenged reactive oxygen species by improving the activities of antioxidant enzymes. Lastly, exogenous BL could cooperate with other endogenous plant hormones, such as indole-3-acetic acid, isopentenyl adenosine, and gibberellic acid 4, that respond to Fe deficiency stress indirectly. This work provided a theoretical basis for the application of exogenous BL to alleviate Fe deficiency stress in apple plants.

Using an improved Si-rich husk ash to decrease inorganic arsenic in rice grain

Paddy rice is efficient at arsenite accumulation by sharing the uptake and transport pathway for silicic acid. To limit As entry into rice by increasing soil Si availability, rice husk with concentrated Si deposition was subject to an ethanol-aided open combustion in this work to promote Si release from organic matrix. Compared to original husk, the content of amorphous silica was almost tripled in the resultant ash (Si-ash) with an apparent elimination of hydrocarbon groups. Following its incorporation into soil, 3.4-fold higher Si dissolution was maintained in rice rhizosphere compared to control, which was accompanied by 15.9-40.5% decrease in porewater As from tillering to harvest. Correspondingly, As sequestration in soil solid phase and root plaque increased by 8.0% and 26.9% with Si-ash, which could result from promoted FeAs co-precipitation by the liming effect of Si-ash and was linked to a notable decline in As transport through node I. Consequently, inorganic As (iAs) in white rice decreased from 0.36 mg kg^-1 in control to 0.17 mg kg^-1 with Si-ash, which is 15% lower than Chinese food safety standard. Results from this study highlight the advantage of Si-ash in securing rice production by mitigating iAs accumulation in white rice with fortified Si nutrition.

Phosphorus and selenium uptake, root morphology, and carboxylates in the rhizosheath of alfalfa (Medicago sativa) as affected by localised phosphate and selenite supply in a split-root system

Low availability of phosphorus (P) is a key limiting factor for the growth of many crops. Selenium (Se) is a nutrient for humans that is acquired predominantly from plants. Localised P and Se supply may affect P- and Se-uptake efficiency. Our aim was to examine the mechanisms of alfalfa (Medicago sativa L.) to acquire P and Se when the elements are heterogeneously or homogeneously distributed in soil, and how P and Se supply affect plant growth and uptake of P and Se. We conducted a split-root experiment growing alfalfa in a loess soil with two distribution patterns (i.e. heterogeneous and homogeneous) of P and Se. The application rates of P (KH2PO4) and Se (Na2SeO3) were 0 and 20mgPkg-1, and 0 and 1mgSekg-1, respectively. Our results showed that plants absorbed more Se when both P and Se were supplied homogeneously than when supplied heterogeneously. Supplying Se had a positive effect on plant P content. Localised P supply resulted in the exudation of more carboxylates by roots than homogeneous P supply did. Soil microbial biomass P was significantly greater when P was supplied homogeneously. Shoot-to-root translocation of Se had a positive effect on P-uptake efficiency. These results indicated that, compared with homogeneous P supply, localised P supply promoted P and Se uptake by increasing the amount of rhizosheath carboxylates and weakening the competition between roots and microbes. Translocation of Se within plant organs was promoted by the application of P, thus enhancing the P-uptake efficiency of alfalfa.

Foliar application of 3-hydroxy-4-pyridinone Fe-chelate [Fe(mpp)3 ] induces responses at the root level amending iron deficiency chlorosis in soybean

Iron (Fe) deficiency chlorosis (IDC) affects the growth of several crops, especially when growing in alkaline soils. The application of synthetic Fe-chelates is one of the most commonly used strategies in IDC amendment, despite their associated negative environmental impacts. In a previous work, the Fe-chelate tris(3-hydroxy-1-(H)-2-methyl-4-pyridinonate) iron(III) [Fe(mpp)3 ] has shown great potential for alleviating IDC in soybean (Glycine max) in the early stages of plant development under hydroponic conditions. Herein, its efficacy was verified under soil conditions in soybean grown from seed to full maturity. Chlorophyll levels, plant growth, root and shoot mineral accumulation (K, Mg, Ca, Na, P, Mn, Zn, Ni, and Co) and FERRITIN expression were accessed at V5 phenological stage. Compared to a commonly used Fe chelate, FeEDDHA, supplementation with [Fe(mpp)3 ] led to a 29% higher relative chlorophyll content, 32% higher root biomass, 36% higher trifoliate Fe concentration, and a twofold increase in leaf FERRITIN gene expression. [Fe(mpp)3 ] supplementation also resulted in increased accumulation of P, K, Zn, and Co. At full maturity, the remaining plants were harvested and [Fe(mpp)3 ] application led to a 32% seed yield increase when compared to FeEDDHA. This is the first report on the use of [Fe(mpp)3 ] under alkaline soil conditions for IDC correction, and we show that its foliar application has a longer-lasting effect than FeEDDHA, induces efficient root responses, and promotes the uptake of other nutrients.

Plasmopara viticola infection affects mineral elements allocation and distribution in Vitis vinifera leaves

Plasmopara viticola is one of the most important pathogens infecting Vitis vinifera plants. The interactions among P. viticola and both susceptible and resistant grapevine plants have been extensively characterised, at transcriptomic, proteomic and metabolomic levels. However, the involvement of plants ionome in the response against the pathogen has been completely neglected so far. Therefore, this study was aimed at investigating the possible role of leaf ionomic modulation during compatible and incompatible interactions between P. viticola and grapevine plants. In susceptible cultivars, a dramatic redistribution of mineral elements has been observed, thus uncovering a possible role for mineral nutrients in the response against pathogens. On the contrary, the resistant cultivars did not present substantial rearrangement of mineral elements at leaf level, except for manganese (Mn) and iron (Fe). This might demonstrate that, resistant cultivars, albeit expressing the resistance gene, still exploit a pathogen response mechanism based on the local increase in the concentration of microelements, which are involved in the synthesis of secondary metabolites and reactive oxygen species. Moreover, these data also highlight the link between the mineral nutrition and plants' response to pathogens, further stressing that appropriate fertilization strategies can be fundamental for the expression of response mechanisms against pathogens.