Differential induction of plant volatile biosynthesis in the lima bean by early and late intermediates of the octadecanoid-signaling pathway

Plants are able to respond to herbivore damage with de novo biosynthesis of an herbivore-characteristic blend of volatiles. The signal transduction in itiating volatile biosynthesis may involve the activation of the octadecano id pathway, as exemplified by the transient increase of endogenous jasmonic acid (JA) in leaves of lima bean (Phaseolus lunatus) after treatment with the macromolecular elicitor cellulysin. Within this pathway lima bean posse sses at least two different biologically active signals that trigger differ ent biosynthetic activities. Early intermediates of the pathway, especially 12-oxo-phytodienoic acid (PDA), are able to induce the biosynthesis of the diterpenoid-derived 4,8,12-trimethyltrideca-1,3,7,11-tetraene. High concen trations of PDA result in more complex patterns of additional volatiles, JA , the last compound in the sequence, lacks the ability to induce diterpenoi d-derived compounds, but is highly effective at triggering the biosynthesis of other volatiles. The phytotoxin coronatine and amino acid conjugates of linolenic acid (e.g, linolenoyl-L-glutamine) mimic the action of PDA, but coronatine does not increase the level of endogenous JA. The structural ana log of coronatine, the isoleucine conjugate of 1-oxoindanoyl-4-carboxylic a cid, effectively mimics the action of JA, but does not increase the level o f endogenous JA. The differential induction of volatiles resembles previous findings on signal transduction in mechanically stimulated tendrils of Bry onia dioica.