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

区分根与根结合时根系对铝离子的反应与根伸长时根系对铝离子的反应对阐明铝耐受性的机制具有重要意义。结果如下：高浓度Al处理的根尖细胞中Al含量与不同种类植物对Al的耐受性呈负相关，但与根尖部分和从根尖部分分离的细胞壁的CECs无关。铝处理后，根尖部分细胞壁CEC变化不大，且与铝耐受性无关。对铝敏感的植物根尖部分钾、磷、镁的浓度在铝处理后显著降低。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，耐铝水稻根系2 mm尖部钾离子和氯离子浓度较高，铝敏感大麦较低。K从根部流出的结果与前者一致。经100 muM Al处理1 h后，任何一种植物根尖细胞的质膜（PM）含量均正常（FDA-PI荧光染色）；在不含铝的培养基中，对铝敏感的植物根系再伸长数小时后，PM受到了相当大的破坏，但在铝处理后，用柠檬酸进行短期后处理，PM的渗透性恢复正常。铝敏感植物根尖原生质体经低渗处理后，其PM的通透性明显降低。在铝敏感植物原生质体中，原生质体与原生质体残体的Al浓度比接近1。根系有机酸释放量的差异，尤其是柠檬酸的释放量的差异，与不同品种和品种对铝的耐受性差异不一致。Al处理后，铝敏感植物根尖细胞的PM更瞬间被Al离子饱和，其渗透性增加，最终在铝敏感植物中显著诱导PM的K渗漏和Al渗透。根系伸长加速铝毒性。根尖细胞的脂质组成可能最终决定铝的耐受性。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