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Importance of the chiral centers of jasmonic acid in the responses of plants. Activities and antagonism between natural and synthetic analogs

Holbrook, L., Tung, P., Ward, K., Reid, D.M., Abrams, S., Lamb, N., Quail, J.W., Moloney, M.M.
Plant physiology 1997 v.114 no.2 pp. 419-428
Helianthus annuus, Nicotiana tabacum, Brassica napus, Triticum aestivum, seed germination, cotyledons, chlorophyll, chemical degradation, measurement, senescence, jasmonic acid, esters, dose response, proteinase inhibitors, gene expression, transgenic plants, beta-glucuronidase, enzyme activity, reporter genes, chemical structure, stereochemistry, chemical constituents of plants
The importance of the two chiral centers at C-3 and C-7 in the molecular structure of jasmonic acid in plant responses was investigated. We separated methyl jasmonate (MeJA) into (3R)- and (3S)-isomers with a fixed stereochemistry at C-3, but epimerization at C-7 is possible. The four isomers of the nonepimerizable analog 7-methyl MeJA were synthesized. These six esters and their corresponding acids were tested in three bioassays: (a) senescence in sunflower (Helianthus annuus) cotyledons; (b) proteinase inhibitor II gene expression in transgenic tobacco (Nicotiana tabacum) with beta-glucuronidase as a biochemical reporter; and (c) seed germination in Brassica napus and wheat (Triticum aestivum). The esters and acids had similar activities in the three assays, with the ester being more effective than its acid. The (3R)-stereochemistry was critical for jasmonate activity. Although activity was reduced after substituting the C-7 proton with a methyl group, the analogs with (3R,7R)- or (3R,7S)-stereochemistry were active in some of the assays. Although the four isomers of 7-methyl MeJA were inactive or only weakly active in the senescence assay, they could overcome the senescence-promoting effect of (3R)-MeJA. The strongest antagonistic effect was observed with the (3R,7S)-isomer.