PLANT PHYSIOLOGY , Vol 114, Issue 2 419-428, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Importance of the Chiral Centers of Jasmonic Acid in the Responses of Plants (Activities and Antagonism between Natural and Synthetic Analogs)
L. Holbrook, P. Tung, K. Ward, D. M. Reid, S. Abrams, N. Lamb, J. W. Quail and M. M. Moloney
Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada T2N 1N4 (L.H., P.T., K.W., D.M.R., M.M.M.)
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.
