Influence of irradiation time and solution concentration on the photochemical degradation of EDDHA/Fe3+: effect of its photodecomposition products on soybean growth

Magnetite nanoparticle coating chemistry regulates root uptake pathways and iron chlorosis in plants

Understanding the fundamental interaction of nanoparticles at plant interfaces is critical for reaching field-scale applications of nanotechnology-enabled plant agriculture, as the processes between nanoparticles and root interfaces such as root compartments and root exudates remain largely unclear. Here, using iron deficiency-induced plant chlorosis as an indicator phenotype, we evaluated the iron transport capacity of Fe3O4 nanoparticles coated with citrate (CA) or polyacrylic acid (PAA) in the plant rhizosphere. Both nanoparticles can be used as a regulator of plant hormones to promote root elongation, but they regulate iron deficiency in plant in distinctive ways. In acidic root exudates secreted by iron-deficient Arabidopsis thaliana, CA-coated particles released fivefold more soluble iron by binding to acidic exudates mainly through hydrogen bonds and van der Waals forces and thus, prevented iron chlorosis more effectively than PAA-coated particles. We demonstrate through roots of mutants and visualization of pH changes that acidification of root exudates primarily originates from root tips and the synergistic mode of nanoparticle uptake and transformation in different root compartments. The nanoparticles entered the roots mainly through the epidermis but were not affected by lateral roots or root hairs. Our results show that magnetic nanoparticles can be a sustainable source of iron for preventing leaf chlorosis and that nanoparticle surface coating regulates this process in distinctive ways. This information also serves as an urgently needed theoretical basis for guiding the application of nanomaterials in agriculture.

Spatiotemporal biocontrol and rhizosphere microbiome analysis of Fusarium wilt of banana

The soil-borne fungus Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana (FWB), which devastates banana production worldwide. Biocontrol is considered to be the most efficient approach to reducing FWB. Here we introduce an approach that spatiotemporally applies Piriformospore indica and Streptomyces morookaensis strains according to their respective strength to increase biocontrol efficacy of FWB. P. indica successfully colonizes banana roots, promotes lateral root formation, inhibits Foc TR4 growth inside the banana plants and reduces FWB. S. morookaensis strain Sm4-1986 secretes different secondary compounds, of which xerucitrinin A (XcA) and 6-pentyl-α-pyrone (6-PP) show the strongest anti-Foc TR4 activity. XcA chelates iron, an essential nutrient in pathogen-plant interaction that determines the output of FWB. 6-PP, a volatile organic compound, inhibits Foc TR4 germination and promotes banana growth. Biocontrol trials in the field demonstrated that application of S. morookaensis lead to improvement of soil properties and increase of rhizosphere-associated microbes that are beneficial to banana growth, which significantly reduces disease incidence of FWB. Our study suggests that optimal utilization of the two biocontrol strains increases efficacy of biocontrol and that regulating iron accessibility in the rhizosphere is a promising strategy to control FWB.

Impacts of iron on phosphate starvation-induced root hair growth in Arabidopsis

In Arabidopsis, phosphate starvation (-Pi)-induced responses of primary root and lateral root growth are documented to be correlated with ambient iron (Fe) status. However, whether and how Fe participates in -Pi-induced root hair growth (RHG) remains unclear. Here, responses of RHG to different Fe concentrations under Pi sufficiency/deficiency were verified. Generally, distinct dosage effects of Fe on RHG appeared at both Pi levels, due to the generation of reactive oxygen species. Following analyses using auxin mutants and the phr1 mutant revealed that auxin and the central regulator PHR1 are required for Fe-triggered RHG under -Pi. A further proteomic study indicated that processes of vesicle trafficking and auxin synthesis and transport were affected by Fe under -Pi, which were subsequently validated by using a vesicle trafficking inhibitor, brefeldin A, and an auxin reporter, R2D2. Moreover, vesicle trafficking-mediated recycling of PIN2, an auxin efflux transporter, was notably affected by Fe under -Pi. Correspondingly, root hairs of pin2 mutant displayed attenuated responses to Fe under -Pi. Together, we propose that Fe affects auxin signalling probably by modulating vesicle trafficking, chiefly the PIN2 recycling, which might work jointly with PHR1 on modulating -Pi-induced RHG.

Fast Determination of a Novel Iron Chelate Prototype Used as a Fertilizer by Liquid Chromatography Coupled to a Diode Array Detector

The environmental risk of the application of synthetic chelates has favored the implementation of new biodegradable ligands to correct Fe-deficient plants. This study developed and validated an analytical method for determination of a new prototype iron chelate─Fe(III)-benzeneacetate, 2-hydroxy-α-[(2-hydroxyethyl)amino]─(BHH/Fe³⁺) based on liquid chromatography with diode array detection, as a potential sustainable alternative. Chromatographic analysis was performed on a LiChrospher RP-18 in reverse-phase mode, with a mobile phase consisting of a mixture of acetonitrile (solvent A) and sodium borate buffer 0.20 mM at pH = 8 (solvent B) at a flow rate of 1.0 mL/min in isocratic elution mode. This method was fully validated and found to be linear from the limit of quantification (LOQ) to 50 mg/L and precise (standard deviation below 5%). The proposed method was demonstrated to be selective, precise, and robust. The developed methodology indicated that it is suitable for the quantification of iron chelate BHH/Fe³⁺.

Implications of the Mn:ligand ratio for Mn uptake by Glycine max L. plants fertilized with heptagluconate and gluconate complexes

BACKGROUND

The environmental risk of the application of synthetic chelates has furthered the implementation of biodegradable complexes to correct manganese (Mn)-deficient plants. This study used the biodegradable ligands of heptagluconate (G7) and gluconate (G6) to test the influence of the Mn2+ :ligand ratio on their fertilizers' capacity to provide Mn to plants. The efficacy of these complexes to correct Mn-deficient soybean was evaluated in hydroponics and calcareous soil conditions and compared with the synthetic chelate EDTA (ethylenediaminetetraacetic acid).

RESULTS

This study demonstrated that G7 was a biodegradable alternative to EDTA for supplying Mn, maintaining an adequate nutritional balance compared with G6, which reduced iron (Fe) uptake by the plants. The efficacy of the Mn complexes depended on both the ligand and the Mn:ligand ratio, with the 1:1 and 1:2 molar ratios of Mn2+ :G7 being the most effective complexes in the short term on the basis of their chemical structure and stability.

CONCLUSION

The Mn2+ :G7 (1:1 and 1:2) complexes were found to be effective Mn sources for plant nutrition due to their chemical structures providing adequate stability in alkaline solution and their fast-action effect. © 2021 Society of Chemical Industry.

Flowering and Seed Production across the Lemnaceae

Plants in the family Lemnaceae are aquatic monocots and the smallest, simplest, and fastest growing angiosperms. Their small size, the smallest family member is 0.5 mm and the largest is 2.0 cm, as well as their diverse morphologies make these plants ideal for laboratory studies. Their rapid growth rate is partially due to the family's neotenous lifestyle, where instead of maturing and producing flowers, the plants remain in a juvenile state and continuously bud asexually. Maturation and flowering in the wild are rare in most family members. To promote further research on these unique plants, we have optimized laboratory flowering protocols for 3 of the 5 genera: Spirodela; Lemna; and Wolffia in the Lemnaceae. Duckweeds were widely used in the past for research on flowering, hormone and amino acid biosynthesis, the photosynthetic apparatus, and phytoremediation due to their aqueous lifestyle and ease of aseptic culture. There is a recent renaissance in interest in growing these plants as non-lignified biomass sources for fuel production, and as a resource-efficient complete protein source. The genome sequences of several Lemnaceae family members have become available, providing a foundation for genetic improvement of these plants as crops. The protocols for maximizing flowering described herein are based on screens testing daylength, a variety of media, supplementation with salicylic acid or ethylenediamine-N,N'-bis(2-hydroxyphenylacetic acid) (EDDHA), as well as various culture vessels for effects on flowering of verified Lemnaceae strains available from the Rutgers Duckweed Stock Cooperative.

Effect of Fe:ligand ratios on hydroponic conditions and calcareous soil in Solanum lycopersicum L. and Glycine max L. fertilized with heptagluconate and gluconate

BACKGROUND

The environmental risk from the application of synthetic chelates has led to the use of biodegradable complexes to correct Fe deficiency in plants. In this article, the Fe oxidation state, the Fe:ligand ratio, and the molecular weight distribution for heptagluconate (G7) and gluconate (G6) are considered as key factors for the efficacy of complexes as fertilizers. Complexes with different Fe:ligand ratios were prepared and analyzed by gel filtration chromatography (GFC). The ability of Fe:ligand ratios to provide Fe to tomato in hydroponics and soybean in calcareous soil was tested and compared with synthetic chelates (Fe3+ :HBED and Fe3+ :EDTA).

RESULTS

G7 presented greater capacity to complex both Fe(II) and Fe(III) than G6, but the Fe(II) complexes exhibited poor stability at pH 9 and oxidation in solution. Gel filtration chromatography demonstrated the polynuclear nature of the Fe3+ :G7 at various ratios. The effectiveness of the Fe fertilizers depend on the Fe3+ :ligand ratio and the ligand type, the Fe3+ :G7 (1:1 and 1:2) being the most effective. Fe3+ :G7 (1:1) also presented a better response for the uptake of other micronutrients.

CONCLUSION

Fe3+ :G7 molar ratios have been shown to be critical for plant Fe uptake under hydroponic conditions and with calcareous soil. Thus, the Fe3+ :G7 at equimolar ratio and 1:2 molar ratio can be an environmentally friendly alternative to less degradable synthetic chelates to correct Fe chlorosis in strategy I plants. © 2019 Society of Chemical Industry.

[S,S]-EDDS/Fe: A new chelate for the environmentally sustainable correction of iron chlorosis in calcareous soil

Iron deficiency in crops is usually prevented and cured by the application of synthetic Fe chelates such as EDTA/Fe and the o,o-EDDHA/Fe. However their persistence in soil calls for the implementation of new alternatives that present less of a risk to the environment. This study therefore evaluated the biodegradable chelating agent [S,S]-EDDS as a new source for Fe fertilisation in calcareous soils in relation to its chemical reactivity. The suitability of [S,S]-EDDS/Fe as an Fe fertiliser in a calcareous soil was investigated and compared to the traditional synthetic chelates EDTA/Fe and o,o-EDDHA/Fe. Plant experiments with soybean (Glycine max), ⁵⁷Fe isotopic labelling, and batch incubations were conducted in a calcareous soil. The Fe concentration of plants treated with [S,S]-EDDS/Fe was similar to those treated with EDTA/Fe. A similar Fe concentration to the o,o-EDDHA/Fe treatment was achieved using a double dose of [S,S]-EDDS/Fe. Despite the degradation of [S,S]-EDDS limiting the durability of [S,S]-EDDS/Fe in soil, the Fe bound to the degradation products may be a determining factor in improving Fe uptake and translocation to leaves in plants treated with [S,S]-EDDS/Fe compared to other Fe sources. Speciation studies by modelling and batch experiments also supported the lower reactivity of [S,S]-EDDS/Fe with calcium compared to that of EDTA/Fe, possibly contributing to the permanence of [S,S]-EDDS/Fe in the calcareous soil. This study demonstrated for the first time, that [S,S]-EDDS may be an environmentally sustainable alternative to traditional synthetic chelating agents such as EDTA or o,o-EDDHA for curing Fe chlorosis in susceptible plants in calcareous soil.

Response of soybean plants to the application of synthetic and biodegradable Fe chelates and Fe complexes

The growing concern over the environmental risk of synthetic chelate application promotes the search for alternatives in Fe fertilization, such as biodegradable chelating agents and natural complexing agents. In this work, plant responses to the application of several Fe treatments (chelates and complexes) was analyzed to study their potential use in Fe fertilization under calcareous conditions. Thus, the root ferric chelate reductase (FCR) activity of soybean (Glycine max cv. Klaxon) plants was determined, and the effectiveness of the Fe chelates and complexes assessed in a pot experiment, by SPAD and fluorescence induction measurements, and the determination of Fe distribution in plant and soil. Additionally, 57Fe Mössbauer spectroscopy was conducted to identify the Fe forms present in the soybean roots. The highest FCR activity was observed for the chelates EDDS/Fe3+ and IDHA/Fe3+; while no activity was observed when using complexes as Fe substrates. In contrast to the FCR data, the pot experiment confirmed that the o,oEDDHA/Fe3+ is the most effective treatment, and the complexes LS/Fe3+ and GA/Fe3+ are able to alleviate Fe chlorosis, also indicated by SPAD data and the maximal quantum efficiency of photosystem II reaction centers as vitality parameters, and the enhanced plant uptake of Fe from natural sources.

Timing for a sustainable fertilisation of Glycine max by using HBED/Fe3+ and EDDHA/Fe3+ chelates

BACKGROUND

Efficient use of Fe chelates is crucial to avoid environmental risks and reduce economic losses. HBED/Fe3+ has been recently approved by the European Union for soil fertilisation, but studies delving into the best timing for its application are necessary. In this work, a batch incubation experiment and two biological experiments were developed to determine the optimal physiological stage for a sustainable application of HBED/Fe3+ in soil fertilisation compared with EDDHA/Fe3+ fertilisers using 57 Fe.

RESULTS

HBED/Fe3+ demonstrated a high durability in soils and soil materials, maintaining more than 80% of Fe chelated after 70 days, and its application at an early physiological stage resulted in a high Fe accumulation in soybean and soil after 36 days. In contrast, the stability of EDDHA/Fe3+ decreased because of the retention of its lowest stable isomers. The best timing for chelates application was confirmed in a 52 day experiment. The application of HBED/Fe3+ at the early stage increased the Fe translocation to fruits; while o,o-EDDHA/Fe3+ accumulated more Fe in fruits when added at the fructification stage.

CONCLUSION

The high HBED/Fe3+ stability in calcareous soil requires a differentiate application timing, and its addition at early physiological stages leads into the most efficient fertilisation. © 2016 Society of Chemical Industry.

EDTA Shuttle Effect vs. Lignosulfonate Direct Effect Providing Zn to Navy Bean Plants (Phaseolus vulgaris L 'Negro Polo') in a Calcareous Soil

Zn-Lignosulfonates (LS) fertilizers are used as an eco-friendly alternative to chelate formulations. The mechanisms of Zn release in the rhizosphere by both types of products are compared. The ability to provide Zn to Phaseolus vulgaris L of non-modified and chemically modified ZnLS and ZnEDTA is compared in a hydroponic assay. Stable isotope ⁶⁷Zn was used to study Zn source (fertilizer, Zn_Fer, or native, Zn_Nat) uptake and distribution in plants in two soil pot experiments. ZnEDTA was the best treatment to provide both Zn_Fer and Zn_Nat to navy bean plants. A shuttle effect mechanism and an isotopic exchange may occur. ZnLS from eucalyptus (ZnLSE) provides more Zn to the plant than LS from spruce. Chemical modifications of ZnLSE does not improve its efficiency. A double dose of ZnLSE provides similar Zn_Fer in leaves and similar soluble Zn_Fer content in soil than ZnEDTA. A model for the Zn fertilizers behavior in the soil and plant system is presented, showing the shuttle effect for the synthetic chelate and the direct delivery in the rhizosphere for the ZnLS complex.