[论文解读] Combined 3D PET and Optical Projection Tomography Techniques for Plant Root Phenotyping

Qiang Wang, Sergey Komarov+5 more|arXiv (Cornell University)|Jan 1, 2015

Plant nutrient uptake and metabolism参考文献 11被引用 4

一句话总结

本研究结合三维正电子发射断层扫描（3D PET）与光学投影断层扫描（OPT），非侵入性地成像玉米植株在透明凝胶培养基中动态的碳分配与根系生长。通过共注册的PET与OPT数据，研究发现根尖11C活性与后续根系生长速率之间存在显著的线性相关性（R² > 0.8），表明PET可在形态学变化于OPT图像中显现前48小时预测侧根的出现。

ABSTRACT

New imaging techniques are in great demand for investigating underground plant roots systems which play an important role in crop production. Compared with other non-destructive imaging modalities, PET can image plant roots in natural soil and produce dynamic 3D functional images which reveal the temporal dynamics of plant-environment interactions. In this study, we combined PET with optical projection tomography (OPT) to evaluate its potential for plant root phenotyping. We used a dedicated high resolution plant PET imager that has a 14 cm transaxial and 10 cm axial field of views, and multi-bed imaging capability. The image resolution is around 1.25 mm using ML-EM reconstruction algorithm. B73 inbred maize seeds were germinated and then grown in a sealed jar with transparent gel-based media. PET scanning started on the day when the first green leaf appeared, and was carried out once a day for 5 days. Each morning, around 10 mCi of 11CO2 was administrated into a custom built plant labeling chamber. After 10 minutes, residual activity was flushed out with fresh air before a 2-h PET scan started. For the OPT imaging, the jar was placed inside an acrylic cubic container filled with water, illuminated with a uniform surface light source, and imaged by a DSLR camera from 72 angles to acquire optical images for OPT reconstruction. The same plant was imaged 3 times a day by the OPT system. Plant roots growth is measured from the optical images. Co-registered PET and optical images indicate that most of the hot spots appeared in later time points of the PET images correspond to the most actively growing root tips. The strong linear correlation between 11C allocation at root tips measured by PET and eventual root growth measured by OPT suggests that we can use PET as a phenotyping tool to measure how a plant makes subterranean carbon allocation decisions in different environmental scenarios.

研究动机与目标

• 开发一种非侵入性、多模态成像方法，用于研究兼具功能与形态分辨率的植物根系表型。
• 探究通过PET测量的动态碳分配与通过OPT测定的实际根系生长速率之间的相关性。
• 评估PET是否可在形态学成像中可见之前，预测未来的根系生长事件（如侧根出现）。
• 通过监测碳分配模式的变化，探究环境胁迫对根系生长动力学的影响。

提出的方法

• 使用配备1.25 mm空间分辨率和14 cm横向×10 cm轴向视野（FOV）的专用高分辨率植物PET扫描仪，对透明凝胶培养基中的玉米根系进行成像。
• 通过定制标记腔每日施加11CO2，随后进行2小时的PET扫描，以追踪实时碳分布。
• 光学投影断层扫描（OPT）通过使用单反相机从72个角度成像同一植株实现，同时将培养罐浸入水中以校正光学畸变。
• 从OPT投影图像重建3D根系结构，并基于光学数据量化根尖位置与生长速率。
• PET与OPT图像的共注册实现了根尖区域11C活性浓度与随时间变化的根系生长速率的直接比较。
• 对根尖周围定义的感兴趣区域（ROIs）内的11C活性与OPT测得的对应根系生长速率进行统计相关性分析。

实验结果

研究问题

• RQ1 3D PET成像能否检测到在形态学变化可见之前，植物根系中动态的碳分配模式？
• RQ2 根尖11C活性浓度与通过OPT测得的实际根系生长速率之间的相关性有多强？
• RQ3 PET是否可在光学成像中可见之前，预测侧根出现事件？
• RQ4 环境约束（如物理障碍）如何影响碳分配与根系生长动力学？如PET与OPT所揭示。

主要发现

• 在24小时时间窗口内，根尖11C活性浓度与通过OPT测得的根系生长速率之间观察到显著的线性相关性（R² > 0.8）。
• PET成像在OPT图像中可见与侧根出现相关的微形态学变化之前，可提前48小时检测到根尖的碳分配信号。
• 遇到物理障碍（如玻璃培养罐壁）的根系在根尖表现出更高的11C活性，表明碳分配增加以支持生长方向的改变。
• 通过定制的放射性示踪剂递送系统，实现了对同一植株的多次无扰动成像，支持根系发育的纵向追踪。
• 共注册的3D PET与OPT图像显示，PET数据中的热点区域对应于最活跃生长的根尖，验证了PET作为功能表型分析工具的有效性。
• 本研究证明，仅使用PET即可潜在地模拟常规土壤中碳分配-生长关系，为实现更精确的生理表型分析提供了新路径。