PHLOEM TRANSLOCATION OF A REDUCED OLIGOGALACTURONIDE IN RICINUS-COMMUNIS L

We have re-examined the evidence against the phloem mobility of oligog alacturonide elicitors using a reduced oligogalacturonide in the phloe m translocation system of Ricinus communis var. Gibsonii. A tritium-la belled end-reduced oligogalacturonide of degree of polymerisation 6 wa s injected into the hollow centre of the petiole of four- to five-week -old plants. Two experimental procedures were followed. In the first, the whole plant was harvested and dissected after 5 h incubation. In t he second, phloem sap was collected from an incision in the main stem below the injected petiole; collection started 2 h after incubation an d continued for a further 3 h. Determination of the total radiolabel p resent in the dissected plant showed that at least 8% of the applied a ctivity was exported from the injected leaf, most of this being recove red from the main stem below the injected petiole and the roots. The a ctivity in the phloem exudate showed that the rate of export of radiol abel was already at its maximum by the end of the 2-h incubation perio d. Radiolabelled material recovered from the main stem was found to be highly comparable to starting material when subjected to thin-layer c hromatography. These results demonstrate the phloem mobility of reduce d oligogalacturonides of low degree of polymerisation and therefore re -establish the potential for oligogalacturonides to act as systemic si gnals.