Callose production as indicator of aluminum toxicity in bean cultivars

The response of seven cultivars of beans to aluminum (A1) stress was assessed by using root elongation rate and callose accumulation in 5 mm root tips as early markers of injury. Bean seedlings were grown in acid nutrient solution (pH 4.5) and exposed to 0, 20, and 50 μM A1 for 24 h. Root elongation was recorded at frequent intervals and callose accumulation was determined spectrofluorometrically. Based on the root elongation rate, Strike and Contender were A1-sensitive and F-15 and Superba were the most A1-tolerant cultivars. The cultivars Hilds maxi, Hinrichs riesen, and Saxa showed an intermediate behavior. Callose synthesis positively correlated with internal A1 concentration and negatively correlated with root elongation rate. Both callose accumulation and root elongation rate were useful in classifying the bean cultivars for aluminum tolerance, but root elongation rate was a more sensitive parameter. Root callose deposition can serve as an early marker for A1 toxicity and tolerance in beans.