The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Japan.
Cryobiofrontier Research Center, Faculty of Agriculture, Iwate University, Morioka, Japan.
Plant Cell Physiol. 2019 Feb 1;60(2):303-317. doi: 10.1093/pcp/pcy210.
Environmental adaptability is essential for plant survival. Though it is well known that a simple cooling or cold shock leads to Ca2+ signals, direct evidence has not been provided that plants use Ca2+ signals as a second messenger in the cold acclimation (CA) process in the field. By developing a technique to analyze Ca2+ signals using confocal cryomicroscopy, we investigated Ca2+ signals under several temperature conditions by combining the start temperature, cooling rate and cooling time duration. In both root and leaf cells, Ca2+ signals rapidly disappeared after cooling stopped, and thereafter under a constant low temperature no Ca2+ signal was observed. Interestingly, under the cooling regime from 2�C to -2�C, non-acclimated plants grown at 23�C hardly showed Ca2+ signals, but cold-acclimated plants at 2�C were able to form Ca2+ signals in root cells. These findings suggest that plants sense temperature decreases with Ca2+ signals while adjusting the temperature sensitivity to their own temperature environment. Furthermore, if the temperature is constant, no Ca2+ signal is induced even during CA. Then, we also focused on the CA under field conditions, rich in temperature fluctuations. In CA under field conditions, the expression patterns of CBF/DREB1 genes were distinctly different from those in artificial CA. Pharmacological studies with Ca2+ channel blockers showed that the Ca2+-induced expression of CBF/DREB1 genes was closely correlated with the amplitude of temperature fluctuation, suggesting that Ca2+ signals regulate CBF/DREB1 gene expression during CA under natural conditions.
环境适应性对于植物的生存至关重要。虽然人们熟知简单的降温或冷休克会引发 Ca2+信号，但目前还没有直接的证据表明植物在野外的冷驯化（CA）过程中会将 Ca2+信号作为第二信使。通过开发一种使用共聚焦冷冻显微镜分析 Ca2+信号的技术，我们结合起始温度、冷却速率和冷却时间持续时间，在几种温度条件下研究了 Ca2+信号。在根和叶细胞中，冷却停止后 Ca2+信号迅速消失，此后在恒定低温下观察不到 Ca2+信号。有趣的是，在从 2°C 到-2°C 的冷却条件下，在 23°C 下生长的未驯化植物几乎没有显示 Ca2+信号，但在 2°C 下驯化的植物能够在根细胞中形成 Ca2+信号。这些发现表明，植物通过 Ca2+信号感知温度下降，同时调整对自身温度环境的温度敏感性。此外，如果温度保持不变，即使在 CA 期间也不会诱导 Ca2+信号。然后，我们还关注了富含温度波动的野外条件下的 CA。在野外条件下的 CA 中，CBF/DREB1 基因的表达模式明显不同于人工 CA。使用 Ca2+通道阻滞剂的药理学研究表明，Ca2+诱导的 CBF/DREB1 基因表达与温度波动幅度密切相关，这表明 Ca2+信号在自然条件下的 CA 期间调节 CBF/DREB1 基因表达。
