37 Epicuticular Wax and eceriferum Mutants

Abstract

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...