Evidence for Physically Distinct Systemic Signalling Pathways in the Wounded Tomato Plant

Abstract The physical pathway of a systemic signal linking local wounding and systemic synthesis of proteinase inhibitors was investigated in tomato (Lycopersicon esculentum Mill. ‘Moneymaker’) plants. Lucifer Yellow was used to visualize wound induced flow in the xylem. Cuts under water or severe wounds (heat or large crushing wounds) induced flows in the xylem to other parts of the plant in a pattern determined by the vascular architecture. The detailed distribution of systemic proteinase inhibitor activity following these wounds was similar to the pattern of wound induced flow in the xylem. Steaming the petiole of the wounded organ did not prevent the systemic induction of proteinase inhibitor by a severe wound. It was concluded that elicitors released by a severe wound were distributed systemically in the xylem. Small crushing wounds did not induce systemic flow in the xylem but did induce proteinase inhibitor activity in organs importing via the phloem. Steaming the petiole of the wounded leaf prevented systemic induction of proteinase inhibitor by small crushing wounds, a result which is consistent with the translocation of elicitors in the phloem. These results indicate the participation of more than one signalling pathway in the systemic induction of proteinase inhibitor synthesis by wounding.