Non-Invasive Determination of Phloem Transport Speed with ¹⁴C

Studying the phloem, the tissue responsible for distributing organic substances between plant organs, presents significant challenges due to its location deep within the plant body and its sensitivity to manipulation. One effective approach to investigate phloem transport is the use of tracers to measure transport speed with a noninvasive approach. This chapter provides a detailed protocol for using ¹⁴C-labeled photoassimilates to study phloem transport velocity. A key advantage of this method is its noninvasive nature, as the isotope is supplied in the form of ¹⁴CO₂, which is assimilated by source leaves and converted into ¹⁴C-labeled sugars. The movement of these labeled sugars is then tracked using photomultiplier-based X-ray detectors positioned near the stem. This method is particularly valuable for researchers without access to ¹¹C generation facilities. It can also be used to study partitioning of photoassimilates among sink organs over time, as well as rates of export from source tissues. Its relatively straightforward methodology makes it suitable for medium-throughput experiments under controlled conditions.