Growth And Physiology Responses To Aluminium Stress In Root Of Picea. Asperata And Pinus Densata

Aluminum (Al) toxicity is an important factor of restricting plant growth and affects crop productivity on acid mineral soils. Despite a lot research efforts for the last 30 years, the mechanisms of Al-induced inhibition and toxicity to root growth are still not well understood.The seedlings of Picea asperata and Pinus densata are employed to study the following index: effects on their roots growth, the determination of toxic sites in the roots, the changes of proline content (a osmotic substance) and antioxidant enzymes activities, and the resistance of application Ca²⁺ to Al³⁺ toxicity. The results showed that there were almost no inhibitory effects of 0.5mM Al³⁺ on the root elongation of Picea asperata and Pinus densata. The elongations of both roots were markedly inhibited by 2.5 mM to 5mM Al³⁺. The length of Pinus densata and Picea asperata root was about 73.9% and 39.1% of the control, respectively, in the presence of 5mM Al³⁺. These data primarily confirmed that the root of Pinus densata is more resistant to Al toxicity than that of Pinus densata. Under 0-5 mM Al³⁺ stress, water contents of the roots remarkably decreased with Al³⁺ concentration increase. The contents of proline and reactive oxygen species (ROS), and antioxidant enzymes activities continuously enhanced with Al³⁺ concentration increase and reached a maximum value at 5mM Al³⁺. The proline content in both roots decreased rapidly in the presence of 10mM Al³⁺. The reason maybe due to the strong damage of cell membrane in the two roots at 10mM Al³⁺ stress induced proline exosmosis. In time cause tests, the antioxidant enzymes activities and ROS contents in both roots increased with Al³⁺ concentrations and reached the maximum at 5 days and decreased after that. These results showed the change processes of the production and scavenging of ROS in both roots during the short time of Al³⁺ stress.Application of higher concentrations Ca²⁺ (15mM or 25mM) could partially or totally alleviate Al³⁺ induced inhibition to the elongation of both roots when Picea asperata and Pinus densata roots in 5mM Al³⁺ stress were simultaneously treated with different concentrations of Ca²⁺. The results indicated that Ca²⁺ appeared an resistence to the inhibition of Al³⁺ on root elongation.