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

Abstract

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.

The binding of aluminum to mugineic acid and related compounds as studied by potentiometric titration

“…The equilibrium formation constant for the dehydrated Al(III)-MA complex has been reported to be smaller than that of the corresponding Fe(III) complex by a factor between 10 6 and 10 8 (Murakami et al 1989), although the thermodynamic formation constants have not been reported. Furthermore, no interaction between Al(III) and MA has been reported on the basis of either physiological or NMR investigations (Chang et al 1988). It is important to clarify whether MAs and NA bind Al(III) under physiological conditions in order to generate a clear understanding of trivalent metal metabolism in higher plants.…”