Wymer C L, Bibikova T N, Gilroy S
Department of Biology, Mueller Lab, Pennsylvania State University, University Park 16802, USA.
Plant J. 1997 Aug;12(2):427-39. doi: 10.1046/j.1365-313x.1997.12020427.x.
In this study, confocal ratio analysis was used to image the relationship between cytoplasmic free calcium concentration ([Ca2+]c) and the development of root hairs of Arabidopsis thaliana. Although a localized change in [Ca2+]c that preceded or predicted the site of root hair initiation could not be detected, once initiated the majority of emerging root hairs showed an elevated [Ca2+]c (> 1 microM) in their apical cytoplasm, compared with 100-200 nM in the rest of the cell. These emerging root hairs then moved into a 3-5 h phase of sustained elongation during which they showed variable growth rates. Root hairs that were rapidly elongating exhibited a highly localized, elevated [Ca2+]c at the tip. Non-growing root hairs did not exhibit the [Ca2+]c gradient. The rhd-2 mutant, which is defective in sustained root hair growth, showed an altered [Ca2+]c distribution compared with wild-type. These results implicate [Ca2+]c in regulating the tip growth process. Treatment of elongating wild-type root hairs with the Ca2+ channel blocker verapamil (50 microM) caused dissipation of the elevated [Ca2+]c at the tip and cessation of growth, suggesting a requirement for Ca2+ channel activity at the root hair tip to maintain growth. Manganese treatment also preferentially quenched Indo-1 fluorescence in the apical cytoplasm of the root hair. As manganese is thought to enter cells through Ca(2+)-permeable channels, this result also suggests increased Ca2+ channel activity at the tip of the growing hair. Taken together, these data suggest that although Ca2+ does not trigger the initiation of root hairs, Ca2+ influx at the tip of the root hair leads to an elevated [Ca2+]c that may be required to sustain root hair elongation.
在本研究中，共聚焦比率分析用于成像拟南芥细胞质游离钙浓度（[Ca2+]c）与根毛发育之间的关系。尽管未能检测到在根毛起始之前或预测根毛起始部位的[Ca2+]c局部变化，但一旦起始，大多数正在长出的根毛在其顶端细胞质中显示出升高的[Ca2+]c（>1微摩尔），而细胞其他部位为100 - 200纳摩尔。这些正在长出的根毛随后进入3 - 5小时的持续伸长阶段，在此期间它们表现出不同的生长速率。快速伸长的根毛在顶端表现出高度局部化的、升高的[Ca2+]c。不生长的根毛没有表现出[Ca2+]c梯度。在持续根毛生长方面存在缺陷的rhd - 2突变体与野生型相比，显示出[Ca2+]c分布改变。这些结果表明[Ca2+]c参与调节顶端生长过程。用Ca2+通道阻滞剂维拉帕米（50微摩尔）处理伸长的野生型根毛会导致顶端升高的[Ca2+]c消散并停止生长，这表明根毛顶端需要Ca2+通道活性来维持生长。锰处理也优先淬灭根毛顶端细胞质中的Indo - 1荧光。由于锰被认为通过Ca(2+)可渗透通道进入细胞，该结果也表明生长中的根毛顶端Ca2+通道活性增加。综上所述，这些数据表明，尽管Ca2+不会触发根毛的起始，但根毛顶端的Ca2+内流会导致[Ca2+]c升高，这可能是维持根毛伸长所必需的。
