Figure 1. Octadecanoid pathway for JA biosynthesis. Linolenic acid (18:3) is converted into 12-oxo-phytodienoic acid (OPDA) within the chloroplast. OPDA is transported via PXA1-dependent and PXA1-independent pathways into the peroxisome, where it is reduced by OPDA reductase (OPR3). The resulting cyclopentanone compound (OPC-8:0) is ligated to CoA prior to entering the -oxidation pathway that yields JA. The three core enzymes in the -oxidation cascade are acyl-CoA oxidase (ACX), multifunctional protein (MFP) and 3-ketoacyl-CoA thiolase (KAT). A thioesterase is presumably involved in releasing JA from CoA. A parallel ‘hexadecanoid’ pathway (not shown) converts 16:3 into JA via a dinor-OPDA intermediate.

Figure 2. Chemical structure of JA and its derivatives. JA produced from the octadecanoid pathway can be further metabolized by several enzymes. MJE, methyl-JA esterase; JMT, JA carboxy methyltransferase; JAR1, JA Resistance1; ST2a, sulfotransferase. Plant defence responses are typically activated by treatment with MeJA, JA or JA-Ile (blue). Coronatine (red) is a phytotoxin produced by virulent strains of Pseudomonas syringae. The structure and biological activity of coronatine is similar to that of JA-Ile. Hydroxyl derivatives of JA may be further metabolized by conjugation to glucose or other sugars (not shown).

Figure 3. Schematic illustration of grafting experiments used to investigate the role of JA in wound-induced systemic expression of defensive proteinase inhibitors (PIs) in tomato. (a) The jai1 mutant, which harbours a null mutation in the Coi1 gene, was used to investigate the role of jasmonate perception in systemic wound signalling; (b) the acx1 mutant, which is defective in the acyl-CoA oxidase step of JA synthesis, was used to study the role of JA production in systemic wound signalling. Scions and rootstocks of the indicated genotype (wild type, green; jai1, red; acx1, yellow) were joined at the graft junction (horizontal bar). Rootstock leaves were mechanically wounded (hatched mark) and PI gene expression in undamaged scion leaves was measured 8 h later by means of ribonucleic acid (RNA) blot analysis. ‘+’ and ‘–’ denote the expression or lack of expression, respectively, of PIs in the undamaged scion leaves. WT, wild type.

Figure 4. Phenotypes of wild type and opr3 mutant flowers. (a) Flowers at stage 12; (b) flowers at anthesis. Pollination did not occur in opr3 plants unless buds had previously been treated with jasmonate (bottom); (c) germination of pollen harvested at anthesis. Reproduced from Stintzi and Browse (2000). With permission from National Academy of Sciences, USA. Copyright 2000.

Figure 5. Model for the involvement of an SCF complex in jasmonate signalling. The SCF complex ubiquitinates a repressor, R, targeting it to the 26S proteasome. In the absence of R transcription factor(s), T, promote expression of the early genes in jasmonate responses. For auxin F=F^TIR1, R=AUX/IAAs and T=ARFs. For jasmonate F=F^COI1 but R and T are unknown (see the text for details).