Department of Physics, University of Tasmania, G.P.O. Box 252C, 7001, Hobart, Tasmania, Australia.
Planta. 1993 Mar;189(3):377-83. doi: 10.1007/BF00194434.
Elongation growth of plant cells occurs by stretching of cell walls under turgor pressure when intermolecular bonds in the walls are temporarily loosened. The acid-growth theory predicts that wall loosening is the result of wall acidification because treatments (including IAA and fusicoccin) that cause lowered wall pH cause elongation. However, conclusive evidence that IAA primarily reduces wall pH has been lacking. Calcium has been reported to stiffen the cell walls. We have used a microelectrode ion-flux measuring technique to observe directly, and non-invasively, the net fluxes of protons and calcium from split coleoptiles of oats (Avena sativa L.) in unbuffered solution. Normal net fluxes are 10 nmol · m(-2) · s(-1) proton efflux and zero calcium flux. The toxin fusicoccin (1 μM) causes immediate efflux from tissue not only of protons, but also of calcium, about 110 nmol · m(-2) · s(-1) in each case. The data fit the "weak acid Donnan Manning" model for ion exchange in the cell wall. Thus we associate the known "acid-growth" effect of fusicoccin with the displacement of calcium from the wall by exchange for protons extruded from the cytoplasm. Application of 10 μM IAA causes proton efflux to increase transiently by about 15 nmol · m(-2) · s(-1) with a lag of about 10 min. The calcium influx decreases immediately to an efflux of about 20 nmol · m(-2) · s(-1). It appears that auxin too causes an "acid-growth" effect, with extruded protons exchanging for calcium in the cell walls.
植物细胞的延伸生长是通过细胞壁在膨压下的拉伸来实现的，此时细胞壁中的分子间键暂时松弛。酸生长理论预测，细胞壁的松弛是由于细胞壁酸化的结果，因为导致细胞壁 pH 值降低的处理（包括 IAA 和 fusicoccin）会导致伸长。然而，缺乏确凿的证据表明 IAA 主要降低细胞壁 pH 值。已经有报道称钙可以使细胞壁变硬。我们使用微电极离子通量测量技术，直接、非侵入地观察和测量未缓冲溶液中燕麦（Avena sativa L.）分裂胚芽鞘中的质子和钙的净通量。正常净通量为 10 nmol·m(-2)·s(-1)质子外排和零钙通量。毒素 fusicoccin（1 μM）会立即引起组织中质子和钙的外流，每种情况的钙通量约为 110 nmol·m(-2)·s(-1)。数据符合细胞壁中离子交换的“弱酸 Donnan Manning”模型。因此，我们将 fusicoccin 已知的“酸生长”效应与钙通过与从细胞质中挤出的质子交换从壁中置换联系起来。应用 10 μM IAA 会导致质子外排暂时增加约 15 nmol·m(-2)·s(-1)，滞后约 10 分钟。钙内流立即减少到约 20 nmol·m(-2)·s(-1)的外排。似乎生长素也会引起“酸生长”效应，挤出的质子与细胞壁中的钙交换。
