Jasmonic acid in wound signal transduction pathways

Wounding induces expression of genes encoding defense‐related proteins involved in wound healing. An intensive survey has been carried out to clarify the initial signal transduction pathways that mediate this stress to expression of genes. In this context, signal molecules that intermediate in the wound signal to cellular response have been actively searched for. Jasmonic acid (JA) has been considered to be a key signal molecule in this pathway. Systemin, ABA, ethylene, and electrical current have been suggested to function by transmitting the wound signal to JA. A mitogen‐activated protein kinase has been shown to respond rapidly to wounding, and proposed to function as one of the key enzymes involved in JA biosynthesis. Transgenic plants overexpressing a gene encoding a Rab‐type, small GTP‐binding protein contained 6‐fold higher levels of cytokinins than wild‐type plants, and responded to wounding by rapidly producing JA and, uncommonly, accumulating salicylic acid (SA), a pathogenic signal. These phenomena observed in the transgenic plants were reproduced when wild‐type plants were wounded in the presence of the synthetic cytokinin, benzylaminopurine, suggesting that cytokinins are indispensable in the control of endogenous levels of JA and SA.