Critical evaluation of three indirect assays for quantifying phytosiderophores released by the roots of Poaceae

Abstract

Indirect assays are commonly used to measure phytosiderophore (PS) concentrations in the root exudates of grasses. The Cu-mobilizing, Cu-CAS and Fe-binding assays are three commonly used assays but there have been few published attempts to validate or calibrate them rigorously. Thus, we undertook to compare, validate and, where appropriate, to improve and/or optimize each assay. Ethylenediamine-N,N′-diacetic acid (EDDA) and N-2- hydroxyethylethylenediamine-N,N′,N′-triacetic acid (HEDTA) bracket deoxymugineic acid for binding strength with both Fe and Cu and were thus used as model ligands. For the Cu-mobilizing assay, reasonable regressions (as R 2) were obtained between measured and known l..