Fine-Tuning of the Cytoplasmic Ca2+ Concentration Is Essential for Pollen Tube Growth
Fine-Tuning of the Cytoplasmic Ca2+ Concentration Is Essential for Pollen Tube Growth
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DOI：
10.1104/pp.109.139329
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发表时间：
2009-07-01
期刊：
影响因子：
7.4
通讯作者：
Takayama, Seiji
中科院分区：
文献类型：
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作者：
Iwano, Megumi;Entani, Tetsuyuki;Takayama, Seiji
在开花植物繁殖过程中，花粉管的生长对于将精子细胞输送到胚珠是至关重要的。先前对长花百合和烟草的体外成像显示，生长中的花粉管在顶端区域表现出集中在顶端的Ca~(2+)浓度([Ca~(2+)])梯度和胞浆[Ca~(2+)]([Ca~(2+)](Cyt))的有规律的振荡。然而，当管子通过柱头生长时(在活体条件下)是否存在这种[钙]梯度和/或[钙](Cyt)振荡仍不清楚。我们利用表达黄色Cameleon 3.60(一种具有大动态范围的荧光钙指示剂)的拟南芥和烟草，在不同条件下监测了花粉管中[Ca~(2+)](Cyt)的动态。在生长的花粉管中，总是观察到尖端聚焦的[Ca~(2+)](Cyt)梯度。然而，在体内条件下生长的拟南芥或烟草花粉管中，或在它们刚刚通过花柱生长后被置于萌发介质中的花粉管中，很少发现有规律的[Ca~(2+)](Cyt)振荡。另一方面，在生长和不生长的花粉管中都观察到了有规律的振荡，但不生长的花粉管的振荡幅度是生长的花粉管的5倍。这些结果表明，花粉管顶端的亚微摩尔[Ca~(2+)](Cyt)是花粉管生长所必需的，而有规律的[Ca~(2+)]振荡不是必需的。接下来，我们使用黄色骆驼4.60监测了内质网[Ca~(2+)]动态([Ca~(2+)](ER))与拟南芥花粉管生长的关系，与黄色卡梅隆3.60相比，黄色卡梅隆对Ca~(2+)的亲和力较低。在半活体条件下生长的花粉管中的[Ca~(2+)](ER)在100~500 mU M之间，此外，ER-型Ca~(2+)-ATPase的抑制剂环匹亚硝酸抑制了花粉管的生长，降低了[Ca~(2+)](ER)。我们的观察结果表明，内质网是花粉管中的一种钙储存库，内质网中对环匹偶氮酸敏感的钙-三磷酸腺苷酶是花粉管生长所必需的。
Pollen tube growth is crucial for the delivery of sperm cells to the ovule during flowering plant reproduction. Previous in vitro imaging of Lilium longiflorum and Nicotiana tabacum has shown that growing pollen tubes exhibit a tip-focused Ca2+ concentration ([Ca2+]) gradient and regular oscillations of the cytosolic [Ca2+]([Ca2+](cyt)) in the tip region. Whether this [Ca2+] gradient and/or [Ca2+](cyt) oscillations are present as the tube grows through the stigma (in vivo condition), however, is still not clear. We monitored [Ca2+](cyt) dynamics in pollen tubes under various conditions using Arabidopsis (Arabidopsis thaliana) and N. tabacum expressing yellow cameleon 3.60, a fluorescent calcium indicator with a large dynamic range. The tip-focused [Ca2+](cyt) gradient was always observed in growing pollen tubes. Regular oscillations of the [Ca2+](cyt), however, were rarely identified in Arabidopsis or N. tabacum pollen tubes grown under the in vivo condition or in those placed in germination medium just after they had grown through a style (semi-in vivo condition). On the other hand, regular oscillations were observed in vitro in both growing and nongrowing pollen tubes, although the oscillation amplitude was 5-fold greater in the nongrowing pollen tubes compared with growing pollen tubes. These results suggested that a submicromolar [Ca2+](cyt) in the tip region is essential for pollen tube growth, whereas a regular [Ca2+] oscillation is not. Next, we monitored [Ca2+] dynamics in the endoplasmic reticulum ([Ca2+](ER)) in relation to Arabidopsis pollen tube growth using yellow cameleon 4.60, which has a lower affinity for Ca2+ compared with yellow cameleon 3.60. The [Ca2+](ER) in pollen tubes grown under the semi-in vivo condition was between 100 and 500 mu M. In addition, cyclopiazonic acid, an inhibitor of ER-type Ca2+-ATPases, inhibited growth and decreased the [Ca2+](ER). Our observations suggest that the ER serves as one of the Ca2+ stores in the pollen tube and cyclopiazonic acid-sensitive Ca2+-ATPases in the ER are required for pollen tube growth.