To reveal the biological role of aluminum (Al)-tolerant mechanism in barley Al toxicity, the Altolerant cultivar Humai 8 and Al-sensitive cultivar Shengxian awnless six-rowed barley (Shengxian 6) were used as experimental materials, and treated with different concentrations of AlCl₃ (0, 50, 100 and 150 μmol/L). The active absorbing area, cell membrane permeability, contents of free proline and malondialdehyde (MDA), and the
activities of superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), Ca²⁺-ATPase, and Mg²⁺-ATPase in primary roots of barley were examined to analyze different effects of Al toxicity on the primary roots of two barley cultivars with different Al-tolerance. The results showed that, compared with the control, the effects of Al toxicity on multiple physiological indexes displayed similar changes in the two barley cultivars with different Altolerance; however, the inhibitory effects of Al toxicity on the active absorbing area, cell membrane permeability, and activities of Ca²⁺-ATPase and Mg²⁺-ATPase in Al-tolerant cultivar Humai 8 were lower than those in Al-sensitive cultivar Shengxian 6, and the activity levels of SOD and CAT in Humai 8 were higher than those in Shengxian 6. By contrast, the contents of free proline and MDA in Shengxian 6 were higher than those in Humai 8. These results suggest that Al-tolerant and Al-sensitive barley cultivars differentially respond to Al toxicity at the physiological level, revealing the role of Al-tolerant mechanisms in barley Al toxicity, and providing a new insight into dissecting Al toxicity and Al-tolerant mechanisms in barley.