Cooke T J, Racusen R H
Symp Soc Exp Biol. 1986;40:307-28.
Cell expansion in many plant structures, including algal rhizoids, fungal hyphae, root hairs, and pollen tubes, is restricted to their apical tips. Endogenous electric fields are seen to accompany polarized growth in all tip-growing cells studied to date. The extensive studies on absorptive tip-growing structures have established that positive currents enter their elongating tips, with a portion of the entry current being carried by a localized calcium influx into the extreme tip. The resulting tip-to-base gradient in calcium concentration appears to be responsible for maintaining polarized growth in these systems, although it is uncertain whether this calcium effect is mediated via either electrophoretic or cytoskeletal mechanisms. In contrast, the few electrical measurements made on photosynthetic cells suggest that the orientation of their transcellular fields is transiently or permanently reversed relative to the fields in absorptive structures. In darkness, microelectrode measurements indicate that the apical tip of the fern filament is 5 mV electronegative relative to the base of the apical cell. This cellular dipole is perceived with the vibrating probe as a focused outward current that departs from the tip region and a more diffuse inward current that enters the lateral sides of the apical cell. The tip current is predominantly composed of protons, as can be identified with various cation-selective electrodes. This proton current is thought to help maintain localized wall expansion in the filament tip. Blue light mediates the major morphogenetic transition in fern gametophytes, i.e. the transition from the tip-growing filament to the planar prothallus. All the above electrical and ionic parameters change in the few minutes of irradiation before the filament tip starts lateral swelling. The plasma membrane at the extreme tip begins to hyperpolarize within 3 s, while the basal region shows a delayed, but greater response. The cellular dipole that had existed in darkness is thus abolished in 10 to 15 min after the start of irradiation. With the vibrating probe a more diffuse pattern of positive currents is observed to emerge from the tip as well as the subapical regions of the apical cell. Simultaneously, proton efflux increases in the subapical region; the resulting decrease in cell wall pH should help plasticize the lateral walls, which may, in turn, facilitate the process of lateral swelling over the next few hours.(ABSTRACT TRUNCATED AT 400 WORDS)
许多植物结构中的细胞扩张，包括藻类假根、真菌菌丝、根毛和花粉管，都局限于它们的顶端。在迄今为止研究的所有顶端生长细胞中，都观察到内源性电场伴随着极化生长。对吸收性顶端生长结构的广泛研究表明，正电流进入其伸长的顶端，一部分进入电流由局部钙流入极端顶端携带。钙浓度从顶端到基部的梯度似乎负责维持这些系统中的极化生长，尽管尚不确定这种钙效应是通过电泳还是细胞骨架机制介导的。相比之下，对光合细胞进行的少数电测量表明，它们跨细胞场的方向相对于吸收性结构中的场是暂时或永久反转的。在黑暗中，微电极测量表明，蕨类植物丝状体的顶端相对于顶端细胞的基部带5 mV负电。这种细胞偶极被振动探针感知为从顶端区域离开的集中向外电流和进入顶端细胞侧面的更分散向内电流。顶端电流主要由质子组成，这可以用各种阳离子选择性电极来识别。这种质子电流被认为有助于维持丝状体顶端局部细胞壁的扩张。蓝光介导蕨类植物配子体中的主要形态发生转变,即从顶端生长的丝状体到扁平原叶体的转变。在丝状体顶端开始侧向肿胀前的几分钟照射时间内，所有上述电和离子参数都会发生变化。极端顶端的质膜在3秒内开始超极化，而基部区域显示出延迟但更大的反应。因此，在照射开始后的10到15分钟内，黑暗中存在的细胞偶极消失。用振动探针观察到，从顶端细胞的顶端以及顶端以下区域出现更分散的正电流模式。同时，顶端以下区域的质子外流增加；细胞壁pH值的降低应有助于使侧壁塑性化，这反过来可能有助于在接下来的几个小时内进行侧向肿胀过程。(摘要截断于400字)
