Ma J F, Hiradate S
Faculty of Agriculture, Kagawa University, Kita-gun, Japan.
Planta. 2000 Aug;211(3):355-60. doi: 10.1007/s004250000292.
The forms of Al for uptake by the roots and translocation from the root to the shoot were investigated in a buckwheat (Fagopyrum esculentum Moench, cv. Jianxi) that accumulates Al in its leaves. The Al concentration in the xylem sap was 15-fold higher in the plants exposed to AlCl3 than in those exposed to an Al-oxalate (1:3) complex, suggesting that the roots take up Al in the ionic form. The Al concentration in the xylem sap was 4-fold higher than that in the external solution after a 1-h exposure to AICl3 solution and 10-fold higher after a 2-h exposure. The Al concentration in the xylem sap increased with increasing Al concentration in the external solution. The Al uptake was not affected by a respiratory inhibitor, hydroxylamine, but significantly inhibited by the addition of La. These results suggest that Al uptake by the root is a passive process, and La3+ competes for the binding sites for Al3+ on the plasma membrane. The form of Al in the xylem sap was identified by 27Al-nuclear magnetic resonance analysis. The chemical shift of 27Al in the xylem sap was around 10.9 ppm, which is consistent with that of the Al-citrate complex. Furthermore, the dominant organic acid in the xylem sap was citric acid, indicating that Al was translocated in the form of Al-citrate complex. Because Al is present as Al-oxalate (1:3) in the root, the present data show that ligand exchange from oxalate to citrate occurs before Al is released to xylem.
在叶片中积累铝的荞麦（苦荞麦，品种为建西）中，研究了铝被根系吸收以及从根向地上部转运的形式。暴露于氯化铝的植株木质部汁液中的铝浓度比暴露于草酸铝（1:3）络合物的植株高15倍，这表明根系以离子形式吸收铝。暴露于氯化铝溶液1小时后，木质部汁液中的铝浓度比外部溶液高4倍，暴露2小时后高10倍。木质部汁液中的铝浓度随外部溶液中铝浓度的增加而增加。铝的吸收不受呼吸抑制剂羟胺的影响，但添加镧后显著受到抑制。这些结果表明，根系对铝的吸收是一个被动过程，并且La3+与铝离子在质膜上竞争结合位点。通过27Al核磁共振分析确定了木质部汁液中铝的形式。木质部汁液中27Al的化学位移约为10.9 ppm，这与柠檬酸铝络合物的化学位移一致。此外，木质部汁液中的主要有机酸是柠檬酸，这表明铝以柠檬酸铝络合物的形式转运。由于铝在根中以草酸铝（1:3）的形式存在，目前的数据表明，在铝释放到木质部之前，草酸根到柠檬酸根的配体交换就已发生。
