The Effect Of Boron On The Oxidation Balance Of Root Tips Under Aluminum Stress In Pea

Aluminum（Al）toxicity is the major limiting factor for plant growth and development in acid soils,which can induce oxidative stress.Present studies have demonstrated that boron（B）supply could alleviate Al toxicity by regulating the rhizosphere p H,pectin content and degree of methylesterification,etc.However,the mechanism that B alleviate Al toxicity in plants are reflected in many aspects.Whether boron can alleviate Al toxicity by regulating the oxidation balance still needs further exploration.In this study,we choose diverse pea cultivars,including Alaska（Al-resistant）,Sima（Al-sensitive）and Zhongwan No.6,as experimental materials to give insight into whether B supply alleviates Al toxicity through affecting oxidative stress.The major results are as follows:1.Effects of B and Al on lateral root growth.Al stress can significantly inhibite the growth of lateral roots and lead to swelling and rupture of root apex,especially in the transition zone,which ameliorated by B supply.2.The relationship between Al and oxidative stress.Al stress can induce oxidative stress.Reactive oxygen species（ROS）,superoxide anion(O₂^·-)and hydroxyl radical（·OH）increased significantly in the root apex of pea,while H₂O₂decreased significantly.However,the fluctuation of them was dependent on distinct root zones and cultivars.3.The relationship between B deficiency and oxidative stress.The results showed that B deficiency did not cause significant changes in ROS and·OH in root apex,but caused significant changes in O₂^·-and H₂O₂.B deficiency led to a decrease in H₂O₂in Alaska root tips and an increase in Sima and Zhongwan No.6.In addition,B deficiency led to a decrease in O₂^·-at root tips of Alaska and Zhongwan No.6 and an increase in Sima.4.The relationship between B and Al-induced oxidative stress.Under Al stress,the reactive oxygen species（ROS）,superoxide anion(O₂^·-)and hydroxyl radical（·OH）were significantly reduced in all zones of pea root apex after B supply,while H₂O₂was significantly increased,indicating that B could ameliorate Al toxicity by mediating the oxidative balance which was disrupted by Al exposure.Al mainly caused larger changes in the transition zone of Al-sensitive cultivars,while Al-resistant cultivars mainly in meristem zones and elongation zones.5.The relationship between Al tolerance and oxidative stress in peas.The results indicated that the damage degree of Al exposure was dependent on distinct root zones and cultivars.The root apex of Alaska and Zhongwan No.6 were probably the most severely affected by Al toxicity in the transition zone and elongation zone,while Sima mainly in the meristem zone and transition zone.And the results showed that the fluctuation of ROS,O₂^·-,·OH and H₂O₂in the transition zone of root apex of Sima（Al-sensitive）were larger than Alaska（Al-resistant）and Zhongwan No.6,while the meristem zone was opposite.It indicated that the transition zone of root apex of Al-sensitive cultivar was the most sensitive to Al toxicity.And the large fluctuation of ROS,O₂^·-,·OH and H₂O₂in the transition zone of root apex could reduce Al resistant.6.The alleviative effects of different B concentrations in distinct Al concentrations.The results indicated that the damage degree of Al exposure was dependent on Al concentration.We have determined the optimum B concentration under different Al concentrations.With 15μmol/L Al exposure,the optimal B concentrations of Alaska and Zhongwan No.6 were 15μmol/L.However,the optimal B concentrations for Alaska,Sima,and Zhongwan No.6 were 25μmol/L under 30μmol/L Al exposure.In summary,Al toxicity induced a significant increase in ROS,O₂^·-and·OH,and a significant decrease in H₂O₂in the root apex of pea,resulting in an imbalance of root apex oxidation,which led to root tip swelling and rupture and root growth inhibition.B can alleviate swelling and rupture of the root apex and maintain normal root growth by reducing the oxidative imbalance caused by Al stress.In addition,the optimal B concentration increased with the increased of Al concentration under different Al concentrations,and was affected by the characteristics of pea cultivars.