Biosynthesis of <i>cis</i>‐Jasmone: a pathway for the inactivation and the disposal of the plant stress hormone jasmonic acid to the gas phase?

Abstract Flowers of Jasminum rincospernum convert deuterium‐labeled jasmonic acid [ 2 H 5 ]‐ 4a and methyl 1,2‐didehy‐drojasmonate [ 2 H 4 ]‐ 8 into labeled cis ‐jasmone [ 2 H 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 dicotyledonous 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 4a via 8 a 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.