ALUMINUM ACCUMULATION AND ASSOCIATED EFFECTS ON (NO3-)-N-15 INFLUX IN ROOTS OF 2 SOYBEAN GENOTYPES DIFFERING IN AL TOLERANCE

A study was conducted to examine aluminum (Al) exclusion by roots of two differentially tolerant soybean (Glycine mar L. Merr.) lines, P1-416937 (Al-tolerant) and Essex (Al-sensitive). Following exposure to 80 mu M Al for up to 2 h, roots were rinsed with a 10mM potassium citrate solution and rapidly dissected to allow estimation of intracellular Al accumulation in morphologically distinct root regions. Using 10 min exposures to 300 mu M (NO3-)-N-15 and dissection, accompanying effects on NO3- uptake were measured. With Al exposures of 20 min or 2 h, there was greater Al accumulation in all root regions of Essex than in those of P1-416937. The genotypic difference in Al accumulation was particularly apparent at the root apex, both in the tip and in the adjacent root cap and mucilage. Exposure of roots to Al inhibited the uptake of (NO3-)-N-15 to a similar extent in all root regions. The results are consistent with Al exclusion from cells in the root apical region being an important mechanism of Al tolerance.