Department of Biological Sciences, Purdue University, 47907, West Lafayette, IN, USA.
Planta. 1988 Aug;175(2):280-9. doi: 10.1007/BF00392438.
A vibrating probe was used to measure extracellular electrical currents around developing somatic embryos in two lines (RCC27, RCC48) of cultured cells of Daucus carota L. at the heart and torpedo stages. At pH 5.5, an inward current of 1.2±0.1 μA·cm(-2) (n=23) was detected at the cotyledon, and an outward current of 1.0±0.1 μA·cm(-2) (n=22) was found at the radicle in torpedostage embryos from the RCC27 line. At a pH of 5.75 the currents increased by 0.2-0.3 μA·cm(-2) (n=60-62). In a few cases an additional small inward current was detected at the tip of the radicle in toepedo-stage embryos from RCC27 line. Such an inward current at the radicle seemed to appear earlier, some time after the heart stage, in embryos from the RCC48 line.Both extracellular pH measurements (using microelectrodes filled with ion-sensitive resin) and ion-substitution studies were carried out in order to ascertain the ionic composition of the currents in torpedo-stage embryos from the RCC27 line. Regions adjacent to the cotyledon and radicle, at the points of current entry and exit, were found to be more acidic by 0.02±0.01 (n=14) and 0.07±0.01 (n=12) pH units, respectively, than the bulk medium. Removal of K(+) from the medium reversibly reduced the currents to about 25% of their original value at both cotyledon and radicle. Deletion of Cl(-) decreased the currents slightly. Removal of Ca(2+) resulted in a rapid doubling of currents. Addition of either N,N'-dicyclohexylcarbodiimide or tetraethyl ammonium chloride substantially reduced overall currents, and their removal resulted in partial recovery of the currents. It is suggested that the inward current at the cotyledon is comprised largely of K(+) influx and the outward current at the radicle is mainly the result of active H(+) efflux.
使用振动探针测量了胡萝卜(Daucus carota L.)培养细胞的两条系(RCC27、RCC48)中处于心形期和鱼雷期的体细胞胚周围的细胞外电流。在 pH 值为 5.5 时,在 RCC27 系鱼雷期胚的子叶处检测到 1.2±0.1 μA·cm(-2)(n=23)的内向电流,在胚根处检测到 1.0±0.1 μA·cm(-2)(n=22)的外向电流。在 pH 值为 5.75 时,电流增加了 0.2-0.3 μA·cm(-2)(n=60-62)。在 RCC27 系鱼雷期胚的胚根尖端偶尔还检测到额外的小内向电流。在 RCC48 系胚中,这种内向电流似乎在心脏期之后更早地出现在胚根处。为了确定 RCC27 系鱼雷期胚中电流的离子组成,进行了细胞外 pH 值测量(使用填充有离子敏感树脂的微电极)和离子替代研究。在电流进出点附近的子叶和胚根区域,与主体介质相比,分别酸性增加了 0.02±0.01(n=14)和 0.07±0.01(n=12)pH 单位。从介质中去除 K(+)可使电流可逆地降低到子叶和胚根处原始值的约 25%。去除 Cl(-)会略微降低电流。去除 Ca(2+)会导致电流迅速增加两倍。添加 N,N'-二环己基碳二亚胺或四乙基氯化铵会大大降低总电流,去除它们会使电流部分恢复。因此,子叶处的内向电流主要由 K(+)内流组成,而胚根处的外向电流主要是主动 H(+)外流的结果。