| Aluminum is the most abundant earth metal elements, often in the form of aluminum silicate or aluminum oxide exist, but under acid conditions can form active aluminum ions dissolved toxic to plants. Aluminum toxicity on root growth inhibition is considered the most important symptoms of aluminum toxicity. As the root tip than in more mature root tissue accumulation of aluminum, so that the root tip is the first site of action of aluminum toxicity. Root border cells from root cap meristem, can regulate the rhizosphere environment, reduce root mechanical resistance, and protect the root tip. By production of aluminum toxicity on root tip, certainly on the growth and development of root border cells can be influenced, and research has found that as the aluminum concentration and treatment time increased, the activity of border cells decreased significantly. Boron is a plant growth essential element, boric acid with the cell wall polysaccharide pectin RG-Ⅱin the formation of ester bonds, so that the cell wall polysaccharide pectin into a network connected to maintain the cell wall structure, to ensure normal function of their play. Current research on the relationship between boron and aluminum reported results are not completely consistent, still need further study. Therefore, sufficient boron and boron deficiency on pea root tip and root border cells in the aluminum stress response, can be explained from the microscopic boron's role in plants under aluminum stress.Through the way to adding in exogenous boron to get sufficient B (addition of H3BO3) and B deficiency (by adding 3-NBA) of pea, In situ (Long-term effects of aluminum) and in ex vivo(Short-term effects of aluminum) conditions of research the effects of boron and aluminum on the survival rate, the total number and activity of root border cells, the different segments of root tips'changes on the total soluble sugars and MDA content,and aluminum in the distribution of different root segments revealed B'role on the aluminum toxicity to plants:under the Al stress, the adding boron can effectively relieve aluminum toxicity; boron deficiency significantly increase the toxicity of aluminum ions. Detailed results are as follows:1.Root border cells in situ under Al stress, the survival rate decreased significantly, indicating that Al on root border cells that have lethal effect. Boron significantly increased the cell survival rate, reduced aluminum stress induced cell death, reduced the Al toxicity; boron deficiency significantly increased total cell number.2.Root border cells in vitro under Al stress, the absorption of Al significantly increased with the increase of concentration of Al.After adding B cells significantly reduced the absorption of Al, while cells under the boron deficiency conditions (by adding 3-NBA) significantly increased the absorption of Al.Under Al stress, the activity of root border cells in vitro decreased with increased concentration of Al.The cell activity increased significantly after adding B compared with the control; in the Al concentration of 250μM, the activity of the cell which is boron deficiency (3-NBA treatment) significantly decreased. Root border cells'in vitro absorption of Al was negatively correlated with cell activity, and the correlation coefficient is 0.8195,indicating the absorption of Al led to cell death.3.Different root segments in situ conditions, the absorption of aluminum in the order of 0-0.25cm> 0.25-0.5cm> 0.5-1.0cm. Under Al stress, adding boron could decrease the root segment 0-0.25cm and 0.25-0.5cm of aluminum content, the root segment in B deficiency conditions (by adding 3-NBA treatment) was significantly increased Al content.The root segment in situ total sugar content were 0-0.25cm<0.25-0.5cm<0.5-1.0cm. Under Al stress, total soluble sugar content increased significantly. Adding boron decreased significantly the total soluble sugar content in root segments, while boron deficiency (3-NBA treatment) significantly increased total soluble sugar content in root segments.MDA content of root segment followed by 0.5-1cm<0.25-0.5cm<0-0.25cm.After adding aluminum, MDA content in the root segment 0-0.25cm and 0.25-0.5cm increased significantly, indicating that the Al caused root segment increasing lipid peroxidation. After adding boron,the MDA content of root segments 0-0.25cm and 0.25-0.5cm decreased significantly, and the root segments 0-0.25cm in boron deficiency (3-NBA treatment) significantly increased MDA content, indicating that boron can be inhibition of Al on membrane injury of root segments, but aggravated this membrane injury in boron deficiency.4.Different root segments in vitro conditions, the absorption of aluminum in the order of 0-0.25cm> 0.25-0.5cm> 0.5-1.0cm. Root segments in vitro under Al stress,the absorption of Al significantly increased with the increase of concentration of Al, Overall, adding boron can significantly reduce the Al content of the root segments, boron deficiency significantly increased Al content in the root segment.Overall, total soluble sugar content of root segments in vitro were 0.5-1.0cm> 0-0.25cm> 0.25-0.5cm.Root in vitro under Al stress, total soluble sugar content increased slightly, and Adding boron can significantly reduce the total sugar content, while boron deficiency (3-NBA treatment) when the aluminum concentration was 500μM significantly increased total soluble sugar content.MDA content of root segments were 0-0.25cm> 0.25-0.5cm> 0.5-1.0cm. After adding Al, MDA content increased slightly. Adding boron decreased MDA content significantly, indicating that B alleviated the aluminum causing lipid peroxidation. when the aluminum concentration was 500μM, the root segment 0-0.25cm and 0.5-1.0cm in boron deficiency significantly increased MDA content.In summary, under Al stress adding boron can significantly alleviate the Al toxicity, while boron deficiency was significantly aggravated Al toxicity. Under Al stress different root segments absorption of aluminum in the order of 0-0.25cm> 0.25-0.5cm> 0.5-1.0cm. It showed that the aluminum ions distributed in the root segment 0-0.25cm which contained root cap and root meristem region. It is inferred that may relate to root cap and root meristem region consisting of parenchyma cell and Low degree of cell maturation.
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