IMAGING THE VASCULAR CONTINUITY OF PRUNUS-AVIUM PETIOLES DURING LEAF SENESCENCE USING NUCLEAR-MAGNETIC-RESONANCE SPECTROSCOPY

Nuclear magnetic resonance (NMR) micro-imaging was used to study the distribution of mobile protons in the petiole and stem of Prunus avium throughout the period of senescence of an attached leaf. The base of the NMR micro-imaging probe was modified to allow access to the coil from below, enabling a branch of the intact tree to be inserted into the probe which, in turn, was inserted into the base of the NMR cryomagnet. A multi-slice image was used to determine the final orientation of the petiole in the probe. NMR spin echo imaging parameters were investigated by using variable relaxation delays (D1) ranging from 0.1 to 4.0 s. Transverse slices of the petiole with a D1 ranging between 1.0 to 4.0 s produced bright images corresponding to the cortex and leaving the xylem vessels as a dark horseshoe-shaped area. Reducing D1 to 0.25 s or 0.1 s produced images with more detail, differentiating the phloem and xylem vessels from the surrounding cortex. A longitudinal slice, 0.5 mm thick, through the stem and subtending petiole was imaged repeatedly over 6 d, during which the leaf senesced and abscinded. The images showed details of the vascular strands in the stem with a section continuous with the petiole. During leaf senescence the development of the abscission zone in the petiole was observed. The petiole remained hydrated throughout leaf senescence, demonstrating the usefulness of NMR imaging to probe the vascular integrity of the intact plant.