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

A study was conducted to examine aluminum (Al) exclusion by roots of t wo differentially tolerant soybean (Glycine mar L. Merr.) lines, P1-41 6937 (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 A l 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, the re was greater Al accumulation in all root regions of Essex than in th ose of P1-416937. The genotypic difference in Al accumulation was part icularly apparent at the root apex, both in the tip and in the adjacen t 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 ar e consistent with Al exclusion from cells in the root apical region be ing an important mechanism of Al tolerance.