Studies on the evasive strategy for acid-soil stress by the extracellular released materials operating in the process of root elongation

(1)Al^&lt；3&gt；：利用Al^&lt；3&gt；3&gt；Yb^&lt；3&gt；根尖原生质体表面合成的β-葡聚糖量大小顺序为Al&Gt；Yb&Gt；La；耐铝植物β-葡聚糖的普遍沉积，而铝敏感植物β-葡聚糖的异质点状沉积。合成的β-葡聚糖由部分1，3-β-葡聚糖组成。FDA处理的根活力大小顺序为Al&lt；Yb&lt；La，根系外部金属积累量大小顺序为Al&gt；Yb&Gt；La。La诱导最严重的是不可逆的质壁分解、根伸长的抑制和根中K的流失。在未合成β-葡聚糖的条件下，原生质体的聚集度较高，顺序为Al&Gt；Yb&Gt；La。这些结果表明，根的外部和顶端的质膜是Al^&lt；3&gt；的主要专化部位。(2)基于根尖质膜表面负性的耐铝根细胞的分离：耐铝性与根尖CEC无关，与质膜负性呈极显著相关。将无毒的Al(OH)3与二氧化硅微球(Al-SMB)混合，Al-SMB的最大正电荷值为5.3。将纯化的根尖原生质体与Al-SMB在此pH下混合，最后通过不连续梯度离心法从根尖底部分离到具有活力的耐铝原生质体。(3)无铝固体基质的制备及根释放有机酸的分析：在SMB中加入营养液，制得琼脂状无铝固体基质，其物理性质与实际土壤条件相吻合。通过过滤Al-SMB收集根中释放的有机酸。(4)耐铝性与有机酸释放的关系

(1) Elucidation of the primary specific site for Al^<3+> : Experiments were carried out by utilizing the difference of the order of ionic potential ; Al^<3+>>Yb^<3+>>La^<3+>. The amount of beta-glucan synthesizd on the surface of protoplasts from root tip was in the order of Al>Yb>La ; a universal deposition of beta-glucan on that from Al-tolerant, but a heterogeneous dotted deposition from al-sensitive plant species. The beta-glucan synthesized was composed in part of 1, 3-beta-glucan. FDA viability of root treated with metals was in the order of Al<Yb<La, and the accumulation of metals in the outer portions of roots was considerable in the order of Al>Yb>La. La induced most heavily the irreversible plasmolysis, the inhibition of root elongation, and the loss of K from roots. The aggregation of protoplasts in non-synthesizing conditions of beta-glucan was higher in the order of Al>Yb>La. These results indicate the plasma membrane of the outer and tip portions of roots as the primary specific site for Al^<3+>. (2) Isolation of Al-tolerant root cells based on the surface negativity of plasma membrane from root tip : Al tolerance was not correlated with CEC of root tip, but megatively correlated with the negativity of plasma membrane. Non-toxic Al(OH)_3 was mixed with silica microbeads (Al-SMB) ; the pH of the highest positive charge of Al-SMB was 5.3. Purified protoplasts from root tip were mixed with Al-SMB at this pH, and finally viable Al-tolerant protoplasts were isolated predominantly in the bottom fraction by centrifuging with a discontinuous gradient. (3) Preparation of solid medium without Al and the analysis of organic acids released from roots : By adding the nutrient solution to SMB, agar-like solid medium without Al was prepered ; physical properties of it resembled the actual soil conditions. Organic acids released from roots were collected by filtering the Al-SMB.(4) Relationship between Al olerance and organic acids rel