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Enzymatic characterisation of high-palmitic acid sunflower (Helianthus annuus L.) mutants

Martinez-Force, E., Alvarez-Ortega, R., Garces, R.
Planta 1999 v.207 no.4 pp. 533-538
Helianthus annuus, mutants, palmitic acid, seeds, enzyme activity, acyltransferases, thiolester hydrolases, plant proteins, palmitoleic acid, lipid metabolism, long chain fatty acids, chemical constituents of plants, phenotype
Two high-palmitic acid sunflower (Helianthus annuus L.) mutants, CAS-5 and CAS-12, have been biochemically characterised. The enzymatic activities found to be responsible for the mutant characteristics are beta-keto-acyl-acyl carrier protein synthetase II (KASII; EC and acyl-acyl carrier protein thioesterase (EC Our data suggest that the high-palmitic acid phenotype observed in both mutant lines is due to the combined effect of a lower KASII activity and a higher thioesterase activity with respect to palmitoyl-acyl carrier protein (16:0-ACP). The level of the latter enzyme appeared to be insufficient to hydrolyse the produced 16:0-ACP completely. As a consequence of this, three new fatty acids appear: palmitoleic acid (16:1 delta9), asclepic acid (18:1 delta11), and palmitolinoleic acid (16:2 delta9 delta12). These fatty acids should be synthesised from palmitoyl-ACP or a derivative by the action of the stearoyl-ACP desaturase, fatty acid synthetase II and oleoyl-phosphatidylcholine desaturase, respectively.