ALUMINUM TOLERANCE OF MAIZE CULTIVARS AS ASSESSED BY CALLOSE PRODUCTION AND ROOT ELONGATION

The differences in Al tolerance between 12 maize cultivars were invest igated using early stress indicators such as relative root elongation rate, induction of callose formation and Al concentrations in 5 mm roo t tips. Plants were grown in nutrient solution (pH 4.3) and exposed to 0 (control), 20 or 50 mu M Al for 24 h. According to the relative roo t elongation rates. Regent, C 525 M and Adour 250 were the most Al-tol erant cultivars, while BR 201 F, Teosinte, Alarik, Burras and HS 7777 were Al-sensitive. Cultivars Brummi, HS 1230, Lixis and Aladin showed an intermediate behaviour. A significant inverse correlation between r elationship root-elongation rates and both Al concentration in root ti ps and callose concentrations could be established. The usefulness of callose as an early indicator of Al stress and the importance of Al ex clusion from root tips as an Al tolerance mechanism are discussed.