Epicuticular wax and eceriferum mutants.

Like most plants, the aboveground surface of Arabidopsis thaliana is covered by a layer of lipids such as fatty acids, fatty aldehydes, primary alcohols, alkanes, secondary alcohols, ketones, and esters. Figure 1 illustrates the chemical structures of some of the principal epicuticular wax components found on the surface of Arabidopsis. The majority of these wax components can be separated in a single chromatographic separation by capillary gas chromatography with a low polarity solid phase (Yang et al. 1992). The use of mass spectrometry coupled to a gas chromatograph has allowed the identification of the individual compounds that make up the epicuticular wax layer of plants (Walton 1990). As shown in Figure 2, Arabidopsis eceriferum ( cer ) mutants are characterized by a bright green color when compared to wild-type plants because the reduced amount of wax deposition on the stem alters the reflection of light such that mutants can be isolated by a simple visual inspection. Epicuticular wax components are derived from very long chain fatty acids. The existence of a fatty acid elongation activity within the endoplasmic reticulum has been demonstrated by the partial purification of a 500-kD enzyme complex that elongates stearyl-CoA (18:0) to eicosanoyl-CoA (20:0) (Bessoule et al. 1989). Partial purifications of fatty acid reductase activities have shown that a fatty acid reductase and a fatty aldehyde reductase activity can be separated by protein fractionation (Kolattukudy 1971). Experiments with particulate cell wall fractions of pea have demonstrated that a fatty aldehyde decarbonylation activity is presumably responsible for the biosynthesis...