It has been proposed that glutathione can relieve the effects of Fe deficiency. This study tested the effects of glutathione foliar treatments to prevent Fe chlorosis, using as positive controls soil and foliar Fe fertilisation. Medicago scutellata plants were grown in soil (5.7% CaCO3) supplemented or not with 4 and 8% CaCO3. Two Fe(III)‐EDDHA soil treatments (5 and 10 mg Fe kg−1), and three foliar treatments (three applications each of 2.14 mM Fe(III)‐EDDHA, 1 mM glutathione, and the previous two combined) were applied. Measurements include leaf chlorophyll and Fe concentrations, biomass, leaf enzymatic and non‐enzymatic antioxidant systems and carboxylates. The addition of CaCO3 caused typical Fe deficiency symptoms, including changes in chlorophyll, Fe, antioxidant systems and carboxylates, which were prevented by soil and foliar Fe fertilisation. The foliar treatment with glutathione also led to higher chlorophyll, leaf extractable Fe and root Fe, as well as decreases in some antioxidant systems, whereas leaf Fe concentrations decreased. The combined foliar application of glutathione and Fe was even more efficient in preventing chlorosis. Including glutathione in foliar fertilisation programs should be considered as an option for Fe chlorosis prevention, especially when relatively large leaf total Fe concentrations occur in the so called chlorosis paradox.

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Two metal-contaminated biosolids-amended soils (moderately and highly contaminated) from the Bromley Sewage Treatment Farm, Christchurch, New Zealand, were used to evaluate the effect of remedial treatments on Ni, Zn, and Cu phytoavailability to sunflower (Helianthus annus L.). Two different chemical treatments (iron waste and treated zeolite), at 2 rates of application (5% and 10% w/w), in combination with 3 rates of a liming material (Ca(OH)2 at 0%, 0.33%, and 0.66% w/w) were evaluated for their metal remediation potential using pot experiments. Under the moderately acidic pH conditions of the original soils (pH 5.4–5.7), neither of the materials had substantial effects on plant metal concentrations, and the application of treated zeolite resulted in a large decrease in plant yield (>60% reduction). However, in the presence of Ca(OH)2, both materials showed some potential for reducing Ni and Zn concentrations in sunflowers compared with Ca(OH)2 alone. The best combinations of zeolite or iron waste with Ca(OH)2 resulted in reductions in shoot Ni concentrations to below the detection limit. For Zn, the best combinations of materials resulted in reductions in sunflower shoot Zn concentrations of 91% for the moderately contaminated soil and 75% for the highly contaminated soil. Combinations of iron waste and Ca(OH)2 in particular resulted in substantial decreases in soluble soil Zn concentrations (>90% reduction) and increases in plant yield (63% increase for highly contaminated soil), attributed to the remediation of Zn toxicity. There was little effect of any treatment on Cu concentration in the sunflower plants.

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The aim of this work was to test the hypothesis that Fe mining sub-products and thiols can alleviate a moderate Fe-de ciency in the Strategy I species soybean (Glycine max) grown in a calcareous soil in greenhouse conditions. MethodsCombinations of three Fe sources [Fe(III)-EDDHA and two Fe mining sub-products, both of them containing Fe oxides and one FeS 2 ], and three thiols (glutathione, dithiothreitol and thiophenol) were applied in solution to the soil, three times in a 55 day period, and different parameters related to Fe de ciency were measured. The thiol-mediated solubilization of Fe from the Fe mining sub-products was assessed by measuring in the solution total Fe and the reducible Fe pool using an Fe(II) chelator. ResultsApplication of Fe-EDDHA, the two Fe mining sub-products and the three thiols relieved the Fe de ciency symptoms to different extents, increased the Fe concentrations and contents throughout the plant and changed the redox state of leaves and roots, as judged from the changes in reduced and oxidized glutathione, ascorbate and antioxidant enzymes. When using Fe(III)-EDDHA, the addition of thiols led to a better leaf regreening. However, the addition of thiols did not cause further regreening in the case of the Fe mining sub-products, in spite of being able to solubilize Fe from them. ConclusionApplication of Fe-mining sub-products, thiols and the combination of Fe(III)-EDDHA and thiols could be used to alleviate moderate Fe de ciency in G. max grown in a calcareous soil.