Arabidopsis thaliana - OPUS - Universität Würzburg

an involvement of AtPLA1-Iγ1 in the biosynthesis of jasmontes. A quadruple mutant
defective in four DAD1-like lipases (AtPLA1-Iβ2, AtPLA1-Iγ1, AtPLA1-Iγ2, AtPLA1-Iγ3)
displayed jasmonate levels similar to the mutant line of AtPLA1-Iγ1 after wounding.
The lipids 16:3/dnOPDA are always esterified in sn2 position of glycerolipids.
Furthermore 16:3/dnOPDA may also serve as substrates for the biosynthesis of
jasmonic acid. The results suggest that, in addition to DAD1 and AtPLA1-Iγ1, still
unidentified enzymes with sn1- and sn2-hydrolase activity are involved in wound- and
pathogen-induced jasmonate formation, indicating functional redundancy within the
lipase family.
To clarify the biosynthesis and storage function of arabidopsides, seedlings of
A.thaliana were incubated with D5-linolenic acid ethyl ester to produce labelling of
complex membrane lipids. Subsequent application of silver nitrate induced the
biosynthesis of jasmonates. The analysis of the complex lipids MGDG, DGDG, PC as
well as OPDA/JA before and after treatment with silver nitrate showed a high
consistency of labelling of the complex lipids 18:3-18:3-MGDG, 18:3-OPDA-MGDG,
arabidopside B (OPDA-OPDA-MGDG) as well as arabidopside G (OPDA-OPDA-
MGDG-OPDA) before application of silver nitrate with labelling of the newly
synthesised OPDA/JA induced by treatment with silver nitrate. The results suggest,
that MGDG-18:3-18:3, 18:3-OPDA-MGDG, arabidopsid B and arabidopsid G are
precursors or metabolites of free OPDA, which is a precursor of JA. Furthermore,
simultaneous decrease of 18:3-18:3-MGDG and concomitant increase of arabidopsid
B and arabidopsid G after application of silver nitrate could be shown. This suggests
synthesis of OPDA/dnOPDA in-situ via the alternative pathway. However, mutants of
13-lipoxygenase 2 (LOX2) possess no esterified dnOPDA/OPDA, but display
wildtype-like concentrations of dnOPDA, OPDA and JA. Hence, in A. thaliana the
formation of dnOPDA/OPDA takes place via the classical „Vick-Zimmerman-
Pathway“ as well as via the alternative pathway.
129