Karcz Waldemar, Burdach Zbigniew
University of Silesia, Faculty of Biology, Department of Plant Physiology, ul. Jagiellonska 28, PL-40032 Katowice, Poland.
J Exp Bot. 2002 May;53(371):1089-98. doi: 10.1093/jexbot/53.371.1089.
The physiological activity of exogenous 4-Cl-IAA, as compared to IAA, was examined in maize coleoptile segments. It was found that in this model system 4-Cl-IAA is much more active in the stimulation of elongation than IAA. Simultaneous measurements of growth and external pH indicated that administration of either IAA or 4-Cl-IAA resulted in medium acidification. The kinetics of the pH changes, however, were faster after the addition of 4-Cl-IAA. In contrast to IAA, the coleoptile segments treated with chlorinated auxin were not able to increase medium pH after its initial drop. The re-addition of IAA after 5 h further enhanced growth over the next 2 h by 31%. By contrast, the re-addition of 4-Cl-IAA at the same time protocol as IAA did not cause an additional effect. The administration of 10 microM IAA induced in maize coleoptile cells a transient depolarization followed by a slow hyperpolarization of their membrane potential. In contrast to IAA, 4-Cl-IAA at 1 microM caused an immediate hyperpolarization of the membrane potential which, on average, was 2-fold greater than for IAA. The results reported here provide further evidence that 4-Cl-IAA is much more active, as compared to IAA, in stimulating the growth of maize coleoptile segments. Although it has not been directly demonstrated here, a plausible interpretation for the high 4-Cl-IAA activity is that, at least in part, it might be caused via a reduced metabolism of 4-Cl-IAA. Furthermore, for the first time, the data show that membrane potential responds to 4-Cl-IAA in a qualitatively different fashion than to IAA. These findings may, in turn, suggest a specific signal transduction pathway to 4-Cl-IAA in maize coleoptile cells.
在玉米胚芽鞘切段中检测了外源4-氯吲哚乙酸（4-Cl-IAA）与吲哚乙酸（IAA）相比的生理活性。发现在该模型系统中，4-Cl-IAA在刺激伸长方面比IAA更具活性。对生长和外部pH的同步测量表明，施用IAA或4-Cl-IAA都会导致培养基酸化。然而，添加4-Cl-IAA后pH变化的动力学更快。与IAA不同，用氯化生长素处理的胚芽鞘切段在初始pH下降后无法提高培养基pH。5小时后重新添加IAA在接下来的2小时内使生长进一步增强了31%。相比之下，按照与IAA相同的时间方案重新添加4-Cl-IAA并未产生额外影响。施用10微摩尔/升的IAA在玉米胚芽鞘细胞中诱导了短暂的去极化，随后其膜电位缓慢超极化。与IAA不同，1微摩尔/升的4-Cl-IAA导致膜电位立即超极化，平均而言比IAA大2倍。此处报道的结果进一步证明，与IAA相比，4-Cl-IAA在刺激玉米胚芽鞘切段生长方面活性更高。尽管此处尚未直接证明，但对4-Cl-IAA高活性的一种合理解释是，至少部分原因可能是4-Cl-IAA的代谢减少。此外，数据首次表明膜电位对4-Cl-IAA的反应在性质上与对IAA的反应不同。这些发现进而可能暗示玉米胚芽鞘细胞中存在一条针对4-Cl-IAA的特定信号转导途径。
