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It is known that phosphorus deficiency results in alterations in the assimilation of nitrogen. An experiment was conducted to investigate mechanisms involved in altered ¹⁵NO⁻₃ uptake, endogenous ¹⁵N translocation, and amino acid accumulation in soybean (Glycine max L. Merrill, cv. Ransom) plants deprived of an external phosphorus supply for 20 d in solution culture. Phosphorus deprivation led to decreased rates of ¹⁵NO⁻₃ uptake and increased accumulation of absorbed ¹⁵N in the root. Both effects became more pronounced with time. Asparagine, the primary transport amino acid in soybean, accumulated in large excess in roots and stems. In roots of phosphorus-deprived plants, concentrations of ATP and inorganic phosphate declined rapidly, but dry weight accumulation was similar to or above that of the control even after 20 d of treatment. Arginine accumulation in leaves was greatly enhanced, even …