NJU-NJFU Joint Institute for Plant Molecular Biology, School of Life Sciences, Nanjing University, Nanjing 210093, China.
Plant Cell Environ. 2012 Nov;35(11):1998-2013. doi: 10.1111/j.1365-3040.2012.02532.x. Epub 2012 May 28.
Cadmium (Cd2+) interferes with the uptake, transport and utilization of several macro- and micronutrients, which accounts, at least in part, for Cd2+ toxicity in plants. However, the mechanisms underlying Cd2+ interference of ionic homeostasis is not understood. Using biophysical techniques including membrane potential measurements, scanning ion-selective electrode technique for non-invasive ion flux assays and patch clamp, we monitored the effect of Cd2+ on calcium (Ca2+) and potassium (K+) transport in root hair cells of rice. Our results showed that K+ and Ca2+ contents in both roots and shoots were significantly reduced when treated with exogenous Cd2+. Further studies revealed that three cellular processes may be affected by Cd2+, leading to changes in ionic homeostasis. First, Cd2+ -induced depolarization of the membrane potential was observed in root hair cells, attenuating the driving force for cation uptake. Second, the inward conductance of Ca2+ and K+ was partially blocked by Cd2+, decreasing uptake of K+ and Ca2+ . Third, the outward K+ conductance was Cd2+ -inducible, decreasing the net content of K+ in roots. These results provide direct evidence that Cd2+ impairs uptake of Ca2+ and K+, thereby disturbing ion homeostasis in plants.
镉（Cd2+）干扰了几种大量和微量元素的吸收、运输和利用，这至少部分解释了 Cd2+对植物的毒性。然而，Cd2+干扰离子稳态的机制尚不清楚。本研究利用膜电位测量、扫描离子选择性电极技术进行非侵入性离子通量测定和膜片钳等生物物理技术，监测了 Cd2+对水稻根毛细胞中钙（Ca2+）和钾（K+）运输的影响。结果表明，用外源 Cd2+处理后，根和地上部分的 K+和 Ca2+含量均显著降低。进一步的研究表明，Cd2+可能通过三种细胞过程影响离子稳态，导致离子稳态的变化。首先，在根毛细胞中观察到 Cd2+诱导的膜电位去极化，减弱了阳离子摄取的驱动力。其次，Cd2+部分阻断了 Ca2+和 K+的内向电导，减少了 K+和 Ca2+的摄取。第三，外向 K+电导是 Cd2+诱导的，减少了根中 K+的净含量。这些结果提供了直接的证据，表明 Cd2+损害了 Ca2+和 K+的摄取，从而扰乱了植物中的离子稳态。
