Biosynthesis of cis-jasmone: A pathway for the inactivation and the disposal of the plant stress hormone jasmonic acid to the gas phase?

Flowers of Jasminum rincospermun convert deuterium-labeled jasmonic acid [H-2(5)]-4a and methyl 1,2-didehydrojasmonate [H-2(4)]-8 into labeled cis-jasmone [H-2(4)]-1. The labeling pattern of the resulting cis-jasmone (1) is consistent with a Grob fragmentation of the didehydrojasmonic acid 8a by decarboxylation after protonation of the keto group. The pathway is also operative in leaves of several higher plants, including mono- and dicotylodonous specimens. In Lima beans besides cis-jasmone (1) an equimolar mixture of trans- and cis-isomers of methyl jasmonate (4) and epi-4, is emitted after treatment with jasmonic acid (4a). The relative ratio of 1 and 4/epi-4 is critically dependent on the concentration of the administered jasmonic acid (4a) and the ambient temperature of the plant. Unlike 4a. the 1,2-didehydrojasmonic acid (8a) is not able to induce volatile biosynthesis. Therefore. the transformation of Ja via 8a into 1 appears to have a special importance for the irreversible inactivation and disposal of the plant stress hormone jasmonic acid to the gas phase and may serve, besides other modes of inactivation, as a shunt in case of high internal of the stress hormone 4a. The conversion of the biologically active jasmonic acid (4a) into the inactive and volatile cis-jasmone (1) is the first example of a disposal of an inactive metabolite of a phytohormone to the gas phase as an infinite sink.