Distribution and Chemical Forms of Aluminum in Roots of Aluminum-Tolerant Rice Cultivar Grown with or without Phosphate Pretreatment

Abstract

The distribution and chemical forms of aluminum (Al) were determined in the roots of the Al-tolerant rice cultivar Arkansas cultured in the presence of Al after being precultured with or without phosphates. Lumogallion staining was used to locate Al, and the highest levels of Al were found in the root cap of the plants precultured with phosphates. High levels of Al were also seen in the apoplasmic areas around epidermal and stelar cells of the primary root, and in the area around stelar cells of the lateral roots. Omission of the phosphate preculture reduced Al levels in the root cap and the areas around the epidermal cells. Chemical speciation of the Al that precipitated in the roots was determined by ²⁷Al magic angle spinning NMR spectroscopy. The spectra demonstrated that the precipitate contained significant levels of Al hydroxides, with Al(OH)₂H₂PO₄ as a minor component. These results suggest that the formation of an Al deposit is the main mechanism of Al tolerance in this plant. Additional Al tolerance may result from the increased Al deposition in the root cap and epidermal apoplasmic area in phosphate-pretreated plants. The formation of Al(OH)₂H₂PO₄ may account for the increased Al deposition.

Acknowledgments