PLANT PHYSIOLOGY , Vol 111, Issue 3 805-812, Copyright © 1996 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
The Impact of Alteration of Polyunsaturated Fatty Acid Levels on C6-Aldehyde Formation of Arabidopsis thaliana Leaves
H. Zhuang, T. R. Hamilton-Kemp, R. A. Andersen and D. F. Hildebrand
Department of Agronomy (H.Z., D.F.H.), Department of Horticulture (T.R.H.-K.), and United States Department of Agriculture (R.A.A.), University of Kentucky, Lexington, Kentucky 40546
C6-aldehydes are synthesized via lipoxygenase/hydroperoxide lyase action on
polyunsaturated fatty acid (PUFA) substrates in plant leaves. The source
pools and subcellular location of the processes are unknown. A close
relationship is found between the composition of PUFA and the composition
of C6-aldehydes. In the current study, this relationship was tested using
the Arabidopsis PUFA mutant lines act1, fad2, fad3 fad5, fad6, and fad7.
The results indicate that C6-aldehyde formation is influenced by the
alteration of C18 PUFA levels. Mutants act1 and fad5, which are deficient
in C16 unsaturated fatty acids, had wild-type levels of C6-aldehyde
production. Mutants deficient in the chloroplast hexadecenoic acid/oleic
acid desaturase (fad6) or hexadecadienoic acid/linoleic acid desaturase
(fad7) had altered C6-aldehyde formation in a pattern similar to the
changes in the PUFA. Mutations that impair phosphatidylcholine desaturase
activity, such as fad2 and fad3, however, resulted in increased E-2-hexenal
formation. The enzymes involved in C6-aldehyde production were partially
characterized, including measurement of pH optima. The differences in
C6-aldehyde formation among the fatty acid mutants of Arabidopsis appeared
not to result from alteration of lipoxygenase/hydroperoxide lyase pathway
enzymes. Investigation of the fatty acid composition in leaf phospholipids,
glycolipids, and neutral lipids and analysis of the fatty acid composition
of chloroplast and extrachloroplast lipids indicate that chloroplasts and
glycolipids of chloroplasts may be the source or major source of
C6-aldehyde formation in Arabidopsis leaves.