Callose production as indicator of aluminum toxicity in bean cultivars

The response of seven cultivars of beans to aluminum (Al) stress was assess ed 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 sol ution (pH 4.5) and exposed to 0, 20, and 50 mu M Al for 24 h. Root elongati on was recorded at frequent intervals and callose accumulation was determin ed spectrofluorometrically. Based on the root elongation rate, Strike and C ontender were Al-sensitive and F-15 and Superba were the most Al-tolerant c ultivars. The cultivars Hilds maxi, Hinrichs riesen, and Saxa showed an int ermediate behavior. Callose synthesis positively correlated with internal A l concentration and negatively correlated with root elongation rate. Both c allose 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 Al toxicity and tolerance in beans.