图3
H⁺和O₂ 流动速率的同时测量.

(a)显微照片显示金属氧电极与玻璃H⁺电极同时测量百合花粉管生长过程中H⁺离子和O₂分子进出的变化；(b)在花粉管线粒体密集区域,
或称固有碱化带区域，同时存在的H⁺外流和O₂内流现象.

2.2 SIET与荧光显微技术结合证明磷脂酰肌醇转运蛋白与根毛发生有关

Vincent 等在鉴定出拟南芥磷脂酰肌醇转运蛋白家族 (PITPs)的一种成份AtSfh1p 之后，将显微荧光技术与SIET
结合，从细胞的内部和外部同时证明AtSfh1p 在根毛顶端生长过程中，具有调节细胞内质膜磷酸肌醇极性运输、Ca²⁺信号传递和细胞骨架的功能.在植物细胞的极性生长机理研究方面向前推进了一步.

拟南芥缺失根毛突变体（AtSfh1p）不仅在根毛形态上有变化，不规则弯曲，失去重力极性；而且在Ca²⁺信号传递方面也有异常^[26].
利用Ca²⁺荧光显微技术可测定细胞内部Ca²⁺浓度梯度，而利用SIET可测得外部Ca²⁺流动情况.结果表明野生型的根毛只有在生长旺盛的顶尖区，Ca²⁺的内流速度快，而突变株的根毛Ca²⁺流动的方向和大小明显不同于野生型的根毛.非重力方向的根毛，四周表面都可以检测到Ca²⁺的内流，而且流速高于野生型的两倍左右. ^[26]

 2.3 多离子电极的同时应用证明Ca²⁺及H⁺在植物感知重力变化中起作用

美国北卡罗来纳州立大学植物系NSCORT
研究组受美国宇航局资助，研究植物感知重力的遗传及生理机理，通过对重力非敏感的拟南芥突变体的研究，许越等发现植物根部在相对于地球重力不同的位置的情况下，其H⁺和Ca²⁺的流动在根部的不同位置呈现出不同的变化，显示出及H⁺和Ca²⁺可能在植物感知重力变化的过程中扮演一定的角色(图4)
^[6].

图4
利用SIET 对重力非敏感植物突变体Ca²⁺及H⁺变化的同时测量.

(a)拟南芥突变体（ARG）及其野生型拟南芥（WS)；(b)ARG在重力变化刺激下的 Ca²⁺及H⁺变化与野生型对照有明显的区别.

3 总结及展望

经过多年的改进，SIET数据的生成、采集以及校准等方面不断得到完善.特别是应用SIET
强大的三维立体测量方式，研究人员可以获得其他电生理技术无法测到的被测样品某些点的特异活性^[8，27-29]. SIET 是一个与膜片钳^[30]无论在时间分辨率还是在空间分辨率上都不相同的技术，但两者在应用过程中可以极好地相互补充.由于SIET
技术的出现，人们对于生物体特异离子转运系统的研究，在灵敏度上，时间和空间分辨率上已经被大大地提高了，并已成熟地与细胞和分子生物学技术、其他电生理技术和显微荧光成像技术配合使用.SIET
技术将在主动运输离子或分子泵和协同运输载体的研究方面发挥重大的作用.

分子生物学的进展使得我们能够对质膜转运载体分子加以确定、克隆和进行可控制的表达.当这些转运载体在分子水平方面通过在酵母、卵细胞等系统中的表达予以鉴定，或者某些细胞成份的物理结构和生理功能阐明之后，SIET
技术的非损伤性，多离子/分子同时测量及灵活的空间测量方式将在细胞和组织水平上的功能鉴定方面发挥重要的、甚至是无法替代的作用.

致谢

感谢匡廷云院士在身患重病的情况下对SIET
技术的关心与支持.同时感谢美国Duke大学裴真明教授所作的有益的讨论. 

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