Abstract
Carbon transport processes in plants can be followed non-invasively by repeated application of the short-lived positron-emitting radioisotope 11C, a technique which has rarely been used with trees. Recently, positron emission tomography (PET) allowing 3D visualization has been adapted for use with plants. To investigate the effects of stem girdling on the flow of assimilates, leaves on first order branches of two-year-old oak (Quercus robur L.) trees were labeled with 11C by supplying 11CO2-gas to a leaf cuvette. Magnetic resonance imaging gave an indication of the plant structure, while PET registered the tracer flow in a stem region downstream from the labeled branches. After repeated pulse labeling, phloem translocation was shown to be sectorial in the stem: leaf orthostichy determined the position of the phloem sieve tubes containing labeled 11C. The observed pathway remained unchanged for days. Tracer time-series derived from each pulse and analysed with a mechanistic model showed for two adjacent heights in the stem a similar velocity but different loss of recent assimilates. With either complete or partial girdling of bark within the monitored region, transport immediately stopped and then resumed in a new location in the stem cross-section, demonstrating the plasticity of sectoriality. One day after partial girdling, the loss of tracer along the interrupted transport pathway increased, while the velocity was enhanced in a non-girdled sector for several days. These findings suggest that lateral sugar transport was enhanced after wounding by a change in the lateral sugar transport path and the axial transport resumed with the development of new conductive tissue.
Highlights
Tree physiology studies have often used the radio-active carbon isotope 14C (e.g., Lockhart et al, 2003; Sloan and Jacobs, 2008; Bonhomme et al, 2010)
Cross-sections of the positron emission tomography (PET) images overlaid on the magnetic resonance imaging (MRI) image of a similar oak tree (Figures 2D,E) illustrate that the tracer was located in the phloem region of the stem, which is represented by the peripheral white band in the MRI image (De Schepper et al, 2012)
Young oak trees showed a sectoriality of assimilate flow, with radiotracer distribution in the stem depending on the node of the labeled branch (Figure 2)
Summary
Tree physiology studies have often used the radio-active carbon isotope 14C (e.g., Lockhart et al, 2003; Sloan and Jacobs, 2008; Bonhomme et al, 2010). The short-lived tracer 11C has a high scientific potential, since tracer dynamics can be observed noninvasively in a plant for an unlimited period, provided the tracer is available (Minchin and Thorpe, 2003) It has been used in very few tree studies (Lang and Minchin, 1986; Jahnke et al., 1998; McQueen et al, 2005). In contrast to single-photon detectors, this system counts events only when two annihilation γ-rays coincide in time Due to this specific characteristic, PlanTIS can provide three-dimensional (3D) images of 11C labeled assimilates without the need for radiation shielding (Jahnke et al, 2009).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
