MODELING THE POTENTIAL FOR BORON AMELIORATION OF ALUMINUM TOXICITY USING THE WEIBULL FUNCTION

Several recent reports have suggested that boron (B) may alleviate the toxic effects of aluminum (A1) on plant growth, providing improved pl ant performance on acid soils. To test this hypothesis, an A1-sensitiv e cultivar of Triticum aestivum L. (cv. Neepawa) was grown in solution culture with 10 concentrations of A1 (0-300 mu M), in the presence of deficient (0 mu M), sufficient (6 mu M), luxury (75 mu M), or toxic ( 750 mu M) concentrations of B. The effects of both A1 and B on the res ponse of roots and leaves to A1 was accurately modeled (R(2) < 0.99) u sing a modified Weibull function. Comparison of best fit function para meters for the response to A1 under varying conditions of B supply fai led to reveal any evidence of B amelioration of A1 toxicity. The combi ned effects of A1 and B were adequately explained by a multiplicative model. Although formation of stable A1-berate complexes could occur in growth solutions under our experimental conditions, varying the suppl y of B had little effect on accumulation of A1 in roots and leaves. In contrast, increasing A1 concentrations in solution resulted in increa sed immobilization of B in roots and decreased accumulation of B in le aves. Growth of plants with elevated B supply resulted in higher conce ntrations of B in roots and leaves without improving growth. We sugges t that previous reports of B amelioration of A1 toxicity must reflect the unique characteristics of soil-based media, and (or) differences a mong species in internal requirements for B and the effects of A1 on B nutrition.