Calcium and Strontium Absorption by Corn Roots in the Presence of Chelates
1976
While chelates have been shown to increase the flux of metal cations into roots, the mechanism has been subject to question. The objective of this research was to characterize the action of chelates on metal cation absorption. Calcium and Sr rather than micronutrient metals were used because some plant roots do not discriminate in their absorption, hence, relative flux of Ca vs. Sr could be used to evaluate uptake mechanisms. The chelates used were: EDTA (ethylenediaminetetraacetic acid), DTPA (diethylenetriaminepentaacetic acid), and HEDTA (hydroxethylenediaminetriacetic acid). Flux into corn (Zea mays L.) roots was determined by monitoring Ca, Sr, and chelate depletion from solution with time. Double labeling of Ca and Sr with ⁴⁵Ca and ⁸⁵Sr was used. Ligand concentrations were measured using Cd titration, ¹⁴C-labeling, and UV-absorption measurements of Cu-ligand complexes. Calcium and Sr were removed from solution more rapidly than the chelate. Only 11 to 16% of the chelating ligand was absorbed over a 5-day period whereas 90% or more of each of Ca and Sr was absorbed. The Ca/Sr ratio of uptake indicated that some of the Ca and Sr was absorbed directly from the chelate. However, where Ca²⁺ was maintained by continual addition, chelated Ca appeared relatively unavailable to the plant.
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