Respired CO₂ in woody tissues can build up in the xylem and dissolve in the sap solution to be transported through the plant. From the sap, a fraction of the CO₂ can either be radially diffuse to the atmosphere or be assimilated in chloroplasts present in woody tissues. These processes occur simultaneously in stems and branches, making it difficult to study their specific dynamics. Therefore, an ¹¹C-enriched aqueous solution was administered to young branches of Populus tremula L., which were subsequently imaged by positron emission tomography (PET). This approach allows in vivo visualization of the internal movement of CO₂ inside branches at high spatial and temporal resolution, and enables direct measurement of the transport speed of xylem-transported CO₂ (v_CO2). Through compartmental modeling of the dynamic data obtained from the PET images, we (i) quantified v_CO2 and (ii) proposed a new method to assess the fate of xylem-transported ¹¹CO₂ within the branches. It was found that a fraction of 0.49 min⁻¹ of CO₂ present in the xylem was transported upwards. A fraction of 0.38 min⁻¹ diffused radially from the sap to the surrounding parenchyma and apoplastic spaces (CO_2,PA) to be assimilated by woody tissue photosynthesis. Another 0.12 min⁻¹ of the xylem-transported CO₂ diffused to the atmosphere via efflux. The remaining CO₂ (i.e., 0.01 min⁻¹) was stored as CO_2,PA, representing the build-up within parenchyma and apoplastic spaces to be assimilated or directed to the atmosphere. Here, we demonstrate the outstanding potential of ¹¹CO₂-based plant-PET in combination with compartmental modeling to advance our understanding of internal CO₂ movement and the respiratory physiology within woody tissues.

中文翻译：

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使用正电子发射断层扫描技术研究木质部转运的11CO2的体内动力学。

木本组织中呼吸的CO ₂可以在木质部中积聚并溶解在树液中，从而通过植物运输。从树液中，一部分CO ₂可以径向扩散到大气中，或者被木质组织中存在的叶绿体吸收。这些过程在茎和枝中同时发生，因此很难研究它们的特定动态。因此，将富集¹¹ C的水溶液施用于白杨的幼枝，随后通过正电子发射断层扫描（PET）对其成像。这种方法允许体内可视化CO ₂的内部运动内部分支以高的空间和时间分辨率，可以直接测量木质部传输的CO ₂（v _{CO 2}）的传输速度。通过对从PET图像获得的动态数据进行分区建模，我们（i）量化了v _{CO 2，}并且（ii）提出了一种评估分支中木质部转运的¹¹ CO ₂命运的新方法。发现存在于木质部中的0.49min ^-1的CO _{2的一部分}向上运输。0.38 min ^-1的一部分从树液径向扩散到周围的实质和质外体间隙（CO _2，PA）被木质组织的光合作用所吸收。木质部转运的CO _2的另外0.12 min ^-1通过外排扩散到大气中。剩余的CO ₂（即0.01 min ^-1）以CO _2，PA的形式存储，表示在实质和质外体空间内被吸收或定向到大气中。在这里，我们展示了^11种基于CO ₂的植物PET结合隔室建模的巨大潜力，以增进我们对木质组织内部CO ₂的内部运动和呼吸生理的理解。