Molecular Cell and Developmental Biology, University of Texas, Austin, TX 78712, USA.
Planta. 2011 May;233(5):911-20. doi: 10.1007/s00425-010-1343-2. Epub 2011 Jan 15.
In single-celled spores of the fern Ceratopteris richardii, gravity directs polarity of development and induces a directional, trans-cellular calcium (Ca(2+)) current. To clarify how gravity polarizes this electrophysiological process, we measured the kinetics of the cellular response to changes in the gravity vector, which we initially estimated using the self-referencing calcium microsensor. In order to generate more precise and detailed data, we developed a silicon microfabricated sensor array which facilitated a lab-on-a-chip approach to simultaneously measure calcium currents from multiple cells in real time. These experiments revealed that the direction of the gravity-dependent polar calcium current is reversed in less than 25 s when the cells are inverted, and that changes in the magnitude of the calcium current parallel rapidly changing g-forces during parabolic flight on the NASA C-9 aircraft. The data also revealed a hysteresis in the response of cells in the transition from 2g to micro-g in comparison to cells in the micro-g to 2-g transition, a result consistent with a role for mechanosensitive ion channels in the gravity response. The calcium current is suppressed by either nifedipine (calcium-channel blocker) or eosin yellow (plasma membrane calcium pump inhibitor). Nifedipine disrupts gravity-directed cell polarity, but not spore germination. These results indicate that gravity perception in single plant cells may be mediated by mechanosensitive calcium channels, an idea consistent with some previously proposed models of plant gravity perception.
在蕨类植物凤尾蕨的单细胞孢子中，重力指导了发育的极性，并诱导了一种定向的、跨细胞的钙离子（Ca(2+)）电流。为了阐明重力如何使这个电生理过程极化，我们测量了细胞对重力向量变化的反应动力学，我们最初使用自参考钙离子微传感器来估计这种变化。为了生成更精确和详细的数据，我们开发了一种硅微加工传感器阵列，该阵列促进了一种片上实验室方法，可以实时同时测量多个细胞的钙离子电流。这些实验表明，当细胞倒置时，依赖重力的极性钙电流的方向在不到 25 秒内反转，并且在 NASA C-9 飞机上进行抛物线飞行期间，钙电流的大小与快速变化的重力加速度平行变化。数据还显示，与从 2g 向微重力过渡的细胞相比，细胞从微重力向 2g 过渡的响应存在滞后，这一结果与机械敏感离子通道在重力响应中的作用一致。钙电流被硝苯地平（钙通道阻滞剂）或曙红黄（质膜钙泵抑制剂）抑制。硝苯地平破坏了重力导向的细胞极性，但不破坏孢子萌发。这些结果表明，单细胞植物细胞中的重力感知可能是由机械敏感的钙离子通道介导的，这一观点与一些先前提出的植物重力感知模型一致。
