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Research Project: Sustainable Production and Pest Management Practices for Nursery, Greenhouse, and Protected Culture Crops

Location: Application Technology Research

Title: The relative sensitivity of marigold vs. tomato to iron (Fe) toxicity is associated with root traits: root-to shoot mass ratio, failure to sequester Fe in roots, and levels of the major Fe-uptake protein, IRT

Author
item KOSTIC, EMINA - University Of Toledo
item HECKATHORN, SCOTT - University Of Toledo
item BAGROWSKI, THOMAS - University Of Toledo
item FRANKLIN, THOMAS - University Of Toledo
item Boldt, Jennifer

Submitted to: Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2022
Publication Date: 9/2/2022
Citation: Kostic, E., Heckathorn, S., Bagrowski, T., Franklin, T., Boldt, J.K. 2022. The relative sensitivity of marigold vs. tomato to iron (Fe) toxicity is associated with root traits: root-to shoot mass ratio, failure to sequester Fe in roots, and levels of the major Fe-uptake protein, IRT. Horticulturae. 8. Article 803. https://doi.org/10.3390/horticulturae8090803.
DOI: https://doi.org/10.3390/horticulturae8090803

Interpretive Summary: Some plants are susceptible to iron (Fe) toxicity, which presents as excess leaf Fe accumulation, followed by photo-oxidative damage and leaf tissue necrosis. Avoidance of Fe toxicity should relate to root Fe-uptake properties, including Fe uptake per unit root and Fe-uptake protein concentrations. However, these properties are rarely measured. Therefore, we compared plant responses to Fe toxicity in marigold (Tagetes erecta), a species more prone to Fe toxicity, with tomato (Solanum lycopersicum) to determine which marigold root responses related to Fe-toxicity sensitivity. Plants were grown at 5, 50, and 500 µM Fe. Biomass decreased at 50 and/or 500 vs. 5 mM Fe in both species. Iron uptake per g root increased with increasing Fe. Iron concentration ([Fe]) in root and shoot tissue increased with Fe availability, with [Fe] much higher in roots than in shoots. Root [Fe] was higher in tomato than marigold , but shoot [Fe] was higher in marigold than tomato . Root protein levels of IRT, the main Fe transporter, decreased from 5 to 50 mM Fe in both species, but further decreased at 500 mM Fe only in tomato. In contrast, FRO, which oxidizes Fe3+ to Fe2+, decreased from 50 to 500 mM Fe in both species, with no decrease from 5 to 50 mM Fe. Unexpectedly, H+-ATPase, which acidifies the rhizosphere, was lowest in both species at 5 mM Fe, with no change from 50 to 500 mM Fe. Marigold was likely more susceptible to Fe toxicity because it could not prevent Fe transport to, and accumulation in, leaves; and its sensitivity to high Fe corresponded to a limited capacity to down-regulate IRT as available Fe increased.

Technical Abstract: Iron (Fe) is an essential plant nutrient, yet Fe toxicity is common in crops and decreases crop growth and yield. The causes of Fe toxicity are not completely understood, including the roles of the root proteins that import Fe from the soil into the roots. We examined responses of tomato and marigold to high Fe, and found that marigold was more sensitive to high Fe because it cannot limit Fe uptake or Fe transport to leaves where it causes damage. This was related to an inability to down-regulate the main Fe-uptake protein in roots. This study provides researchers with a better understanding of how Fe toxicity occurs and which traits to target to improve plant resilience to high Fe conditions.