Clarification of the mechanism of Al tolerance operated while both binding with root and elongation of root.

区分根与根结合时和根伸长时根系对铝离子的反应，对阐明植物耐铝机理具有重要意义。结果如下。高浓度铝处理的根尖细胞铝含量与植物耐铝性呈负相关，但与根尖细胞及根尖细胞壁CEC均无相关性。根尖细胞壁CEC在铝处理后变化不大，与耐铝性也不相关。铝处理显著降低了铝敏感植物根尖部K、P、Mg的含量。在水稻、玉米、豌豆、小麦和高粱等铝敏感品种中也观察到同样的趋势。EPMA分析表明，20 μ M铝处理1 h后，耐铝水稻根尖2 mm处的K和Cl浓度较高，而铝敏感大麦根尖2 mm处的K和Cl浓度较低。根系K素流出量与前一结果一致。渗透性 关于我们 在100 μ M铝处理1h后，任何植物根尖细胞质膜（PM）的完整性均正常（FDA-PI荧光染色）;在不含铝的培养基中，根再伸长数小时后，铝敏感植物的PM被相当大的破坏，但在用Al处理之后用柠檬酸进行短期后处理恢复了其正常的渗透性。从铝敏感植物根尖细胞分离的原生质体，经铝处理后再经低渗处理，质膜透性明显增加，铝敏感植物原生质体与原生质体膜的铝浓度比接近1。根系释放有机酸，特别是柠檬酸的量的差异并不对应于植物种和品种之间的耐铝性差异。铝处理后，铝敏感植物根尖细胞质膜被铝离子饱和的时间较短，质膜透性增强，导致铝敏感植物质膜钾渗漏和铝渗透。根的伸长促进铝毒。根尖细胞质膜的脂质组成可能是决定耐铝性的最终因素。少

Discrimination of the responses of root to Al ions while binding with root from that while root elongation is important to clarify the mechanism of Al tolerance. Results are as follows. Al content in root-tip cells treated with high concentration of Al correlated negatively with Al tolerance among plant species, but did not correlate with CECs both of root-tip portion and cell wall isolated from root-tip portion. CEC of cell wall from root-tip portion hardly changed after Al treatment, and did not correlated with Al tolerance, either. The concentrations of K,P and Mg in root-tip portion considerably decreased with Al treatment in Al-sensitive plant species. The same tendency was observed in Al-sensitive cultivars of rice, maize, pea, wheat and sorghum. The concentrations of K and Cl in 2 mm tip-portion of roots treated with 20 muM Al for 1 h were higher in Al-tolerant rice, but lower in Al-sensitive barley by EPMA analysis. Efflux of K from root agreed with the former result. Permeabil … More ity of the plasma membrane (PM) of root-tip cells in any kind of plant species was normal just after the treatment with 100 muM Al for 1 h (FDA-PI fluorescence staining) ; destruction of the PM was considerable in Al-sensitive plant speecies following several hours of re-elongation of root in the medium without Al, but a short-term post-treatment with citric acid following the treatment with Al restored its normal permeability. The permeability of PM of protoplasts isolated from root-tip cells of Al-sensitive plant species was considerably incteased after hypotonic treatment without Al following a temporaty treatment with Al. Al concentration ratio of protoplasts to protoplast ghosts was nearly one in Al-sensitive plant species. Differences in amounts of the release of organic acids, especially citric acid, from roots did not correspond to the differences in Al tolerance among plant species and cultivars. PM of root-tip cells of Al-sensitive plants may be saturated with Al ions more instantly after Al treatment, increased its permeability, and finally K leakage and Al permeation from PM may be induced considerably in Al-sensitive plants. Elongation of root accelerates Al toxicity. Lipid composition of PM of root-tip cells may finally determine Al tolerance. Less