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.