Effect of Al on the phytosiderophore-mediated solubilization of Fe and uptake of Fe-phytosiderophore complex in wheat (Triticum aestivum)

The effect of Aluminum (Al) on phytosiderophore-mediated solubilization of insoluble Fe and the uptake of phytosiderophore-Fe³⁺ complex was examined in wheat (Triticum aestivum L. cv. Atlas 66). Al addition did not affect the Fe solubilization by 2'-deoxymugineic acid (DMA), although Cu addition significantly inhibited the solubilization capacity. Addition of ten times more Al than Fe to the solution of DMA-Fe³⁺ complex did not decrease the absorption of the DMA-Fe³⁺ complex at 375 nm. Furthermore, NMR study indicated that Al did not shift the proton chemical shifts of DMA. All these results suggest that Al could not form a complex with the phytosiderophore, and is thereby unlikely to affect the process of phytosiderophore-mediated solubilization of Fe. Exposure of root to Al up to 100 μM for 3 h did not inhibit the DMA-Fe³+ uptake by the roots, but longer pretreatment (> 6 h) inhibited the uptake of the DMA-Fe³⁺ by more than 50%. Neither the uptake of DMA-Fe³⁺ nor root elongation was inhibited by 24 h pretreatment with 10 μM Al, but both uptake and root elongation were inhibited by higher Al (> 20 μM) pretreatment. These results suggest that Al did not directly block the transport of the phytosiderophore-Fe³⁺ complex, and that the decreased uptake of the phytosiderophore-Fe³⁺ complex resulted from the roots being damaged by Al.