CALCIUM-INDUCED MODIFICATION OF ALUMINUM TOXICITY IN SORGHUM GENOTYPES

Effects of calcium (1, 2 and 5 mM) and aluminum (0, 15 and 45-mu-M) on growth and internal nutrient concentrations were examined with 12 sorghum genotypes (Sorghum bicolor (L.) Moench) in a nutrient solution experiment with a factorial design. At 1 (or 2) mM Ca the severity of root damage induced by Al well reflected the genotypical variation in growth response to Al toxicity. Severity of Al-induced root damage slightly decreased with increasing Ca level. Moreover, Ca at 5 mM amplified the Mg deficiency induced by Al, as seen from both heavier deficiency symptoms and lower internal Mg concentrations. Under conditions of Al stress at a high Ca supply, induced Mg deficiency apparently predominated the genotypical differentiation in growth response to Al toxicity. An antagonism between Al- and Ca ions for uptake was hardly found with the sorghum genotypes. However, the genotypes differed in Ca efficiency, a characteristic which may be relevant in assessing their sensitivity to Mg deficiency.