Zhang Wen-Hao, Walker N Alan, Patrick John W, Tyerman Stephen D
Department of Horticulture, Viticulture and Oenology, The University of Adelaide, Waite Campus PMB 1, Glen Osmond, SA 5064, Australia.
J Exp Bot. 2004 May;55(399):993-1001. doi: 10.1093/jxb/erh120. Epub 2004 Mar 26.
Seed coat cells in the developing seeds of grain legumes release nutrients to the developing embryo. This occurs into an apoplastic space that separates the maternal (seed coat) and filial (embryo) generations. Protoplasts of seed coat cells from coats of Phaseolus vulgaris L. seeds were isolated and whole-cell current across their plasma membranes was characterized using the patch-clamp technique. A pulsing inward current that displayed a spontaneous activation and voltage-dependent inactivation was observed. The frequency and magnitude of the current pulses were positively dependent on cytoplasmic Cl(-) concentrations and independent of external cations. The pulse current was inhibited by DIDS and La(3+), but not by Gd(3+). Single channel events (conductance=18 pS) could be identified with the inactivating phase of the pulses. Together, these findings are consistent with the current being carried by a burst of Cl(-) efflux through Cl(-)-permeable channels that activate almost simultaneously. Neomycin caused a reversible inhibition of the pulsed current, suggesting that its activation is likely to be modulated by an IP(3)-dependent intracellular Ca(2+) release. The pharmacological profiles of Cl(-) efflux from excised seed coats were comparable with those of the Cl(-) channels in the whole cell configuration, suggesting that the Cl(-) channels may underpin Cl(-) efflux from the seed coats. Efflux of Cl(-) from the seed coats was also stimulated by hypo-osmotic treatment as was the frequency and magnitude of Cl(-) channel in whole-cell patch clamp experiments. This implies that the Cl(-) channels responsible for the pulsed Cl(-) currents are likely to be a component of the turgor-regulatory mechanism in developing bean seeds.
豆科谷物发育种子中的种皮细胞会向发育中的胚释放营养物质。这一过程发生在一个质外体空间中，该空间将母本（种皮）和子代（胚）世代分隔开来。从菜豆种子的种皮中分离出种皮细胞的原生质体，并使用膜片钳技术对其质膜上的全细胞电流进行了表征。观察到一种呈现出自发激活和电压依赖性失活的脉冲内向电流。电流脉冲的频率和幅度与细胞质Cl⁻浓度呈正相关，且与外部阳离子无关。脉冲电流受到DIDS和La³⁺的抑制，但不受Gd³⁺的抑制。在脉冲的失活阶段可以识别出单通道事件（电导 = 18 pS）。这些发现共同表明，该电流是由几乎同时激活的Cl⁻通透通道的一阵Cl⁻外流所携带。新霉素对脉冲电流产生可逆性抑制，这表明其激活可能受IP₃依赖性细胞内Ca²⁺释放的调节。从离体种皮中Cl⁻外流的药理学特征与全细胞配置中Cl⁻通道的特征相当，这表明Cl⁻通道可能是种皮中Cl⁻外流的基础。低渗处理也刺激了种皮中Cl⁻的外流，全细胞膜片钳实验中Cl⁻通道的频率和幅度也受到了刺激。这意味着负责脉冲Cl⁻电流的Cl⁻通道可能是发育中豆科种子膨压调节机制的一个组成部分。
