Ward, J. L.; Gaskin, P.; Beale, M. H.; Sessions, R.; Koda, Y.; Wasternack, C.; Molecular modelling, synthesis and biological activity of methyl 3-methyljasmonate and related derivatives Tetrahedron 53, 8181-8194, (1997) DOI: 10.1016/S0040-4020(97)00485-7
Methyl 3-methyljasmonate was synthesised from methyl jasmonate via methyl 3,7-dehydrojasmonate. Molecular modelling predicted an increase in the proportion of cis-orientated side-chains for equilibrated 3-methyl-substituted jasmonate. The synthetic 3-methyljasmonate was shown by gc-ms analysis to equilibrate to a 2:1 ratio of isomers, which appeared from the NMR spectra to comprise mainly the cis-isomer. Surprisingly, both 3,7-dehydro- and 3-methyl-derivatives were inactive in four well established jasmonate bioassays. Methyl-2-methyljasmonate was synthesised and also found to be inactive. Methyl 4,5-dehydrojasmonate was prepared, via the 5-diazo derivative. Both of these compounds have low activity. Our results are discussed with reference to previous knowledge of jasmonate structure-activity relationships and indicate that there are stringent steric demands in jasmonate-receptor interactions.
Kogel, K.-H.; Ortel, B.; Jarosch, B.; Atzorn, R.; Schiffer, R.; Wasternack, C.; Resistance in barley against the powdery mildew fungus (Erysiphe graminis f.sp.hordei) is not associated with enhanced levels of endogenous jasmonates Eur. J. Plant Pathol. 101, 319-332, (1995) DOI: 10.1007/BF01874788
Onset of acquired resistance of barley (Hordeum vulgare) chemically induced by 2,6-dichloroisonicotinic acid (DCINA) correlated with the accumulation of mRNA homologous to cDNA pHvJ256 which codes for a soluble leaf-thionin with a Mr. of 6 kDa [Wasternacket al., 1994a]. In the present work, we extend this finding by showing that the thionin transcript also accumulated following treatment of barley with the resistance-inducing compounds 3,5-dichlorosalicylic acid (DCSA), salicylic acid (SA), and an extract fromBacillus subtilis. The polypeptide showed antifungal activity against the biotrophic cereal pathogensErysiphe graminis f.sp.hordei andPuccinia graminis f.sp.tritici which may indicate a possible role in the mechanism of acquired resistance in barley. A thionin transcript hybridizing to pHvJ256 accumulated also in response to application of jasmonates, or treatments that elevated endogenous amounts of the plant growth substance, pointing to the possibility that signaling mediating defense responses in barley involves jasmonates. However, a topical spray application of jasmonic acid (JA) or jasmonate methyl ester (JM) did not protect barley leaves against infection byE. graminis. Performing a kinetic analysis by an enzyme immunoassay specific for (−)-JA, (−)-JM, and its amino acid conjugates, accumulation of jasmonates was detected in osmotically stressed barley but not at the onset of chemically induced or genetically based resistance governed by the powdery mildew resistance genesMlg, Mla 12, ormlo 5. Furthermore, the jasmonate-inducible proteins JIP-23 and JIP-60 were strongly induced following JM- but not DCINA-treatment or inoculation withE. graminis. Hence, in barley, no indications were found in favour for the previously proposed model of a lipid-based signaling pathway via jasmonates mediating expression of resistance in plants against pathogens.