Department of Soil, Crop and Atmospheric Sciences, USDA-ARS, Cornell University, 14853, Ithaca, NY, USA.
Planta. 1992 Oct;188(3):414-21. doi: 10.1007/BF00192809.
The effects of aluminum on the concentration-dependent kinetics of Ca(2+) uptake were studied in two winter wheat (Triticum aestivum L.) cultivars, Al-tolerant Atlas 66 and Al-sensitive Scout 66. Seedlings were grown in 100 μM CaCl2 solution (pH 4.5) for 3 d. Subsequently, net Ca(2+) fluxes in intact roots were measured using a highly sensitive technique, employing a vibrating Ca(2+)-selective microelectrode. The kinetics of Ca(2+) uptake into cells of the root apex, for external Ca(2+) concentrations from 20 to 300 μM, were found to be quite similar for both cultivars in the absence of external Al; Ca(2+) transport could be described by Michaelis-Menten kinetics. When roots were exposed to solutions containing levels of Al that were toxic to Al-sensitive Scout 66 but not to Atlas 66 (5 to 20 μM total Al), a strong correlation was observed between Al toxicity and Al-induced inhibition of Ca(2+) absorption by root apices. For Scout 66, exposure to Al immediately and dramatically inhibited Ca(2+) uptake over the entire Ca(2+) concentration range used for these experiments. Kinetic analyses of the Al-Ca interactions in Scout 66 roots were consistent with competitive inhibition of Ca(2+) uptake by Al. For example, exposure of Scout 66 roots to increasing Al levels (from 0 to 10 μM) caused the K m for Ca(2+) uptake to increase with each rise in Al concentration, from approx. 100 μM in the absence of Al to approx. 300 μM in the presence of 10 μM Al, while having no effect on the V max. The same Al exposures had little effect on the kinetics of Ca(2+) uptake into roots of Atlas 66. The results of this study indicate that Al disruption of Ca(2+) transport at the root apex may play an important role in the mechanisms of Al toxicity in Al-sensitive wheat cultivars, and that differential Al tolerance may be associated with the ability of Ca(2+)-transport systems in cells of the root apex to resist disruption by potentially toxic levels of Al in the soil solution.
研究了两种冬小麦（Triticum aestivum L.）品种，耐铝性 Atlas 66 和铝敏感 Scout 66 中铝对 Ca(2+)摄取浓度依赖性动力学的影响。幼苗在 100 μM CaCl2 溶液（pH 4.5）中生长 3 天。随后，使用高度敏感的技术，通过振动 Ca(2+)-选择性微电极测量完整根系中的净 Ca(2+)通量。对于外部 Ca(2+)浓度从 20 到 300 μM 的根尖细胞，在不存在外部 Al 的情况下，Ca(2+)摄取的动力学对于两种品种都非常相似；Ca(2+)转运可以用米氏-门捷列夫动力学来描述。当根系暴露于对铝敏感的 Scout 66 有毒但对 Atlas 66 无毒的 Al 水平的溶液中（总 Al 为 5 至 20 μM）时，观察到 Al 毒性与 Al 诱导的根尖 Ca(2+)吸收抑制之间存在很强的相关性。对于 Scout 66，暴露于 Al 会立即且剧烈地抑制整个实验所用 Ca(2+)浓度范围内的 Ca(2+)摄取。在 Scout 66 根中对 Al-Ca 相互作用的动力学分析表明，Al 对 Ca(2+)摄取具有竞争性抑制作用。例如，将 Scout 66 根系暴露于不断增加的 Al 水平（从 0 到 10 μM）会导致 Ca(2+)摄取的 K m 值随着 Al 浓度的每次升高而增加，从无 Al 时的约 100 μM 增加到有 10 μM Al 时的约 300 μM，而对 V max 没有影响。相同的 Al 暴露对 Atlas 66 根系中 Ca(2+)摄取的动力学几乎没有影响。本研究的结果表明，Al 在根尖对 Ca(2+)转运的破坏可能在铝敏感小麦品种的铝毒性机制中起重要作用，并且铝耐性的差异可能与根尖细胞的 Ca(2+)转运系统抵抗土壤溶液中潜在毒性水平的 Al 破坏的能力有关。
