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Phosphate Fixation by Aluminum in Plant Roots¹

ABSTRACT

Although the exact physiological mechanism of Al toxicity is unknown, experiments have indicated that Al reduces the uptake of phosphates in plants. The suspected sites of Al-phosphate interaction are within the root tissue and along the root surface. The present investigation was designed to identify by photomicrographic techniques the sites of phosphate fixation by Al within plant roots. Following pretreatment immersion of barley (Hordeum vulgare) and poplar (Poplus sp.) in solutions containing various concentrations of Al and phosphate, whole roots and sections of root tissues were selectively stained by using a modified Mo blue method to detect the location of phosphate. Color photomicrographs of the root section showed a definite interaction of Al and phosphate in the root cap and in the epidermal and cortical regions extending back from the root tip 1 to 5 mm. The Al-phosphate interaction appeared to be associated with the cell wall and cytoplasmic membrane of the epidermal and cortical cells. Results also indicated that Al adsorbed by the root surface or in the intracellular free space may be capable of immobilizing phosphate present in the root tissue or in the external substrate.

Contribution from the School of Forest Resources, Pennsylvania State Univ. Agr. Exp. Sta., University Park, Penn. 16802. Journal paper no. 4131. Presented before Div. S-4, Soil Sci. Soc. Amer., New York City, N.Y. on Aug. 19, 1971.

² Instructor in Forestry and Associate Professor of Forestry, respectively, School of Forest Resources.

Received for publication March 13, 1972. Accepted for publication May 16, 1972.