Structure-activity relationships of cyclopentane analogs of jasmonic acid for induced responses of canola seedlings, Brassica napus L.

Jasmonic acid (JA) has potent activity in enhancing cotyledon toughness and stimulating the biosynthesis of 3-indolymethyl glucosinolate in seedlings of canola, Brassica napus L. Structure-activity relationships among cyclopentane analogs of JA revealed that maximum activity in both systems was achieved when an acetyl side chain (or a methylated acetyl side chain) occurred at the C-1 ring position, an n-pentenyl side chain at the C-2 ring position, and a keto group at the C-3 ring position. Although coronatine and coronafacic acid both possess a cyclopentane ring with a keto group at the C-3 position, only coronatine was active in B. napus seedlings. Coronatine, a chlorosis-inducing toxin essential to the infectivity of pathovars of Pseudomonas syringae, acted as a complete molecular mimic of JA and had the same stimulatory effect on specific indole glucosinolates in Brassica species, thereby casting doubt on the hypothesis that indole glucosinolates serve in bacterial pathogen defense. Similarities and differences for structural requirements for activity among several diverse physiological systems affected by jasmonates likely reflect species-, tissue-, and developmental-specific differences.