Genes, Elongases and Associated Enzyme Systems in Epicuticular Wax Synthesis

  • Penny von Wettstein-Knowles


Elongases are enzyme complexes which condense short carbon chains to a primer and prepare the growing chain for the next addition. Soluble plastid fatty acid synthetase (FAS) in higher plants is a special example in which the initial primer is acetyl-acyl carrier protein (ACP), the donor of C2-units is malonyl-ACP and the product palmityl-ACP. Addition of another C2-unit to give stearoyl-ACP is not accomplished by FAS but by the soluble plastid palmityl elongase1,2. Epidermal cells of leek appear to lack the latter complex3. Other elongases are generally believed to be located within the epidermal cells wherein they are affiliated with or are part of the microsomal membranes4,5,6,7. Such complexes carry out the elongation steps required to synthesize the very long chains characteristic of the epidermal waxes. Coenzyme A (CoA) rather than ACP derivatives are thought to serve as substrates for the elongases4,5,6,7,8. The latter fall into two groups depending on whether they use acyl-CoA or β-ketoacyl-CoA chains as primers9,10,11. Before arriving on the outermost surface of the cuticle wall, the long acylCoA chains normally enter an associated enzyme system. Attention has been focused on two such complexes using acyl elongase products4. The reductive system yields aldehydes plus free and esterified primary alcohols. The decarboxylative system, named for the apparent decarboxylation that occurs, gives rise to the hydrocarbons, secondary alcohols and ketones. Elongated acyl-CoA compounds not entering one of the associated pathways may appear in the epicuticular wax as free acids. While these are interpreted as leftovers4, they are occassionally the major lipid class in a wax as, for example, on leaf sheaths of sorghum12. By contrast, such left-overs have not been detected coming from ²-ketoacyl elongase products13. All the latter enter one of two associated enzyme systems which will be detailed below.


Primary Alcohol Fatty Acid Synthetase Reductive Pathway Ester Alcohol Major Lipid Class 
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Copyright information

© Plenum Press, New York 1987

Authors and Affiliations

  • Penny von Wettstein-Knowles
    • 1
    • 2
  1. 1.Department of PhysiologyCarlsberg LaboratoryCopenhagenDenmark
  2. 2.Institute of GeneticsUniversity of CopenhagenCopenhagenDenmark

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