Mechanism of aluminum injury and tolerance in plant in terms of the function of plasma membrane.

为了研究小麦（Triticum aestivum L.）耐铝性（Atlas 66）和铝敏感性（Scout 66）的机制，研究了酸性条件下铝胁迫的早期反应。10 μ M的AlCl_3处理3 h以内，对Scout的根伸长有明显的抑制作用。用10 μ M的AlCl_3处理6 h以上，Atlas的根伸长仅受到部分抑制。Atlas根的两个部分，即距根尖0-5 mm和5-10 mm处的Al水平低于Scout。pH值的降低会导致两个品种中K^+外流的增加，在pH值为4.2时，Scout的外流速率是Atlas的两倍。在pH 4.2时，低至5 μ M的AlCl_3明显抑制K^+外流，这种作用在Scout中更为明显。Ca^<2+>也有 关于我们 K^+外流的抑制作用。钒酸盐增加了K^+外流，这一结果表明H^+泵参与了K^+外流。这些结果表明，细胞外低pH值可能会导致细胞质中H^+浓度的增加，随后质膜去极化，这可能会被K^+和H^+的流出所改变。在低pH条件下Atlas和Scout的K^+流出特征差异可能是由质膜电位的差异引起的。<45>不同品种对铝的敏感性不同。钙通道阻滞剂苄普地尔和铝抑制了这两个品种的流入。在此基础上，我们从细胞学角度探讨了铝抑制根伸长的机理。铝对伸长区的细胞伸长有明显的抑制作用，但细胞直径增大。木质化的伸长区正好与抑制两个品种的根生长不同的铝敏感性。少

In order to characterize the mechanism of Al tolerance (Atlas 66) and Al sensitivity (Scout 66) in two cultivars of wheat (Triticum aestivum L.), the early responses to Al stress under acidic conditions were investigated. Marked inhibition of root elongation of Scout was observed upon treatment with 10muM AlCl_3 for less than 3 h. Root elongation of Atlas was only partially inhibited by the treatment with 10muM AlCl_3 for more than 6 h.Levels of Al in two portions of roots, namely, portions 0-5 mm and 5-10 mm from the tip, were lower in Atlas than those in Scout.Both Atlas and Scout were preloaded with K^+ at pH 5.5 and transferred to distillled water at various pH values to monitor the efflux of K^+. A reduction in the pH induced increases in the efflux of K^+ in both cultivars, and the rate of efflux in Scout was twice that in Atlas at pH 4.2. AlCl_3 at concentrations as low as 5muM markedly repressed K^+ efflux at pH 4.2 and this effect was more pronounced in Scout. Ca^<2+> also had … More a repressive effect of K^+ efflux. Vanadate increased K^+ efflux, a result that suggests the involvement of a H^+ pump in K^+ efflux. These results suggest that a low extracellular pH may cause an increase in the cytoplasmic concentration of H^+ that is followed by depolarization of the plasma membrane, which may be modified by the efflux of K^+ and H^+. The characteristic defference in terms of K^+ efflux between Atlas and Scout at low pH may be caused by differences associated with plasma membrane potentials.We compared the effect of aluminum on the calcium (^<45>Ca^<2+>) influx through putative calcium channels of plasma membrane vesicles isolated from two wheat (Triticum aestivum L.) cultivars differing in Al sensitivity. Bepridil, a calcium channel blocker, and aluminum suppressed the influx in both cultivars. However, no differences were observed in the effects of these treatments between the two cultivars.Furtheremore, we investigated the mechanism of the inhibition of root elongation by Al from the cellular point of view. Al inhibit the cell elongation at the elongation zone specifically, where cell elongation was markedly inhibited but the cell diameter increased. Lignification in the elongation zone coincided with an inhibition of root growth of two cultivars differing in Al-sensitivity. Less