盐胁迫下水稻叶肉细胞叶绿体的三维超微结构变化。
Three-dimensional ultrastructural change of chloroplasts in rice mesophyll cells responding to salt stress.
机构信息
Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan.
High Voltage Electron Microscope Laboratory, Institute of Materials and Systems for Sustainability, Nagoya University, Nagoya, Japan.
出版信息
Ann Bot. 2020 Apr 25;125(5):833-840. doi: 10.1093/aob/mcz192.
BACKGROUND AND AIMS
Excess salinity inhibits the metabolism of various systems and induces structural changes, especially in chloroplasts. Although the chloroplast body seems to swell under salinity stress as observed by conventional transmission electron microscopy, previous studies are limited to 2-D data and lack quantitative comparisons because specimens need to be sliced into ultrathin sections. This study shows three-dimensionally the structural changes in a whole mesophyll cell responding to salinity stress by serial sectioning with a focused ion beam scanning electron microscope (FIB-SEM) and compares the differences in chloroplast structures based on reconstructed models possessing accurate numerical voxel values.
METHODS
Leaf blades of rice plants treated with 100 mm NaCl or without (control) for 4 d were fixed chemically and embedded in resin. The specimen blocks were sectioned and observed using the FIB-SEM, and then the sliced image stacks were reconstructed into 3-D models by image processing software.
KEY RESULTS
On the transverse sections of rice mesophyll cells, the chloroplasts in the control leaves appeared to be elongated meniscus lens shaped, while those in the salt-treated leaves appear to be expanded oval shaped. The 3-D models based on serial sectioning images showed that the chloroplasts in the control cells spread like sheets fitted to the shape of the cell wall and in close contact with the adjacent chloroplasts. In contrast, those in the salt-stressed cells curled up into a ball and fitted to cell protuberances without being in close contact with adjacent chloroplasts. Although the shapes of chloroplasts were clearly different between the two treatments, their volumes did not differ.
CONCLUSIONS
The 3-D reconstructed models of whole rice mesophyll cells indicated that chloroplasts under salt stress conditions were not swollen but became spherical without increasing their volume. This is in contrast to findings of previous studies based on 2-D images.
背景与目的
过量的盐分会抑制各种系统的代谢，并导致结构变化，尤其是在叶绿体中。尽管常规透射电子显微镜观察到盐胁迫下叶绿体似乎会膨胀，但以前的研究仅限于二维数据，并且由于需要将标本切成超薄切片，因此缺乏定量比较。本研究通过聚焦离子束扫描电子显微镜（FIB-SEM）的连续切片，三维显示了整个叶肉细胞在盐胁迫下的结构变化，并基于具有准确数值体素值的重建模型比较了叶绿体结构的差异。
方法
用 100 mM NaCl 或不处理（对照）处理 4 天的水稻叶片进行化学固定和树脂包埋。用 FIB-SEM 对标本块进行切片和观察，然后用图像处理软件将切片图像堆栈重建为 3-D 模型。
主要结果
在水稻叶肉细胞的横切面上，对照叶片中的叶绿体呈拉长的新月形透镜状，而盐处理叶片中的叶绿体呈膨胀的椭圆形。基于连续切片图像的 3-D 模型显示，对照细胞中的叶绿体像贴合细胞壁形状的薄片一样展开，并与相邻的叶绿体紧密接触。相比之下，盐胁迫细胞中的叶绿体卷曲成一个球，不与相邻的叶绿体紧密接触，而是贴合到细胞突起上。尽管两种处理下叶绿体的形状明显不同，但它们的体积没有差异。
结论
整个水稻叶肉细胞的 3-D 重建模型表明，盐胁迫下的叶绿体没有膨胀，而是变成了球形，而其体积没有增加。这与以前基于二维图像的研究结果相反。
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