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Background and aims <p>Iron (Fe) toxicity in lowland rice is caused by high Fe levels and mineral imbalances within plants. Thus, maintaining whole-plant mineral balance may be crucial for tolerance. However, there is limited evidence from field studies on elemental profiling that elucidates specific tolerance mechanisms. Here, we tested whether contrasting Fe tolerance mechanisms are associated with distinct patterns of nutrient uptake and distribution.</p> Methods <p>We conducted multi-season experiments in Fe-toxic fields in Madagascar using rice genotypes with contrasting tolerance mechanisms. Elemental profiling was conducted for different parts of shoot tissues. Belowground Fe dynamics were investigated by measuring Fe plaque formation on roots and rhizosphere Fe<sup>2</sup>⁺ levels.</p> Results <p>During the vegetative stages, tolerant genotypes that maintain low shoot Fe concentrations (excluders) showed a 48% reduction in shoot Fe uptake compared to other genotypes, while the uptake of other nutrients was less affected. Tolerant genotypes showed distinct within-plant nutrient allocation patterns. Excluders maintained lower Fe<sup>2</sup>⁺ concentrations in the rhizosphere soil solution, as well as high root:shoot Fe concentration ratios. A mathematical model of the effects of Fe oxidation on soil pH and cation exchange could explain the decreased uptakes of Fe and other cations by excluders.</p> Conclusion <p>Genotypes with different tolerance levels and mechanisms exhibited distinct elemental profiles throughout growth. Genotypes with the same tolerance strategy may rely on distinct physiological mechanisms. Excluders selectively excluded Fe compared to other elements likely mediated by rhizosphere Fe oxidation.</p>

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Elemental profiling reveals rhizosphere oxidation-mediated selective Fe exclusion mechanisms against Fe toxicity in rice in Madagascar

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月4日

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  • Toavintsoa Rajonandraina,
  • Yoshiaki Ueda,
  • Hanna Manwaring,
  • Tovohery Rakotoson,
  • Diarikanto Ny Avo Rafearivo,
  • Takanori Okamoto,
  • Tendro Radanielina,
  • Andry Andriamananjara,
  • Tantely Razafimbelo,
  • Matthias Wissuwa,
  • Guy J. D. Kirk

摘要

Background and aims

Iron (Fe) toxicity in lowland rice is caused by high Fe levels and mineral imbalances within plants. Thus, maintaining whole-plant mineral balance may be crucial for tolerance. However, there is limited evidence from field studies on elemental profiling that elucidates specific tolerance mechanisms. Here, we tested whether contrasting Fe tolerance mechanisms are associated with distinct patterns of nutrient uptake and distribution.

Methods

We conducted multi-season experiments in Fe-toxic fields in Madagascar using rice genotypes with contrasting tolerance mechanisms. Elemental profiling was conducted for different parts of shoot tissues. Belowground Fe dynamics were investigated by measuring Fe plaque formation on roots and rhizosphere Fe2⁺ levels.

Results

During the vegetative stages, tolerant genotypes that maintain low shoot Fe concentrations (excluders) showed a 48% reduction in shoot Fe uptake compared to other genotypes, while the uptake of other nutrients was less affected. Tolerant genotypes showed distinct within-plant nutrient allocation patterns. Excluders maintained lower Fe2⁺ concentrations in the rhizosphere soil solution, as well as high root:shoot Fe concentration ratios. A mathematical model of the effects of Fe oxidation on soil pH and cation exchange could explain the decreased uptakes of Fe and other cations by excluders.

Conclusion

Genotypes with different tolerance levels and mechanisms exhibited distinct elemental profiles throughout growth. Genotypes with the same tolerance strategy may rely on distinct physiological mechanisms. Excluders selectively excluded Fe compared to other elements likely mediated by rhizosphere Fe oxidation.