Wax synthesis in Brassica oleracea as modified by trichloroacetic acid and glossy mutations

Two different mutations in Brassica oleracea, gl₅ and gl₄ have been re-investigated using acetate-1-¹⁴C labelling in an attempt to define more closely the nature of the genetic blocks to wax synthesis. It has been found that gl₅ is a mutation which blocks elongation in the Step C₂₈–C₃₀. The mutation gl₄ exhibits no elongation block and could be blocked in the decarboxylation Step C₃₀–C₂₉. 0·1 mM TCA supplied in the culture solution of cauliflower seedlings affected the leaf surface by producing a glossy appearance similar to that induced by gl₃ and gl₄. At this concentration growth was not inhibited and the appearance of the plants was normal except for the surface wax. The amount of surface wax produced was about 40% of that in untreated seedlings on a leaf area basis. Slight, but significant changes in wax composition were noted, mainly involving a reduction in C₃₀ acids and aldehydes, a slight reduction (33–29%) in alkane content, and a marked difference in chain length composition of the alkanes with C₂₇ increased relative to C₂₉. Over a range of concentrations from 0·1–1 mM, TCA inhibited incorporation of label from acetate-1-¹⁴C into C₃₀ acids and aldehydes more than into C₂₈ at concentrations 0·4–0·8 mM while label tended to accumulate in C₂₄ and C₂₆ acids; thus elongation C₂₈–C₃₀ was especially sensitive to TCA. TCA also inhibited incorporation into primary alcohols and esters almost as much as into C₂₉ compounds. In spite of relatively specific effects on incorporation of label into longer chain lengths, the resulting block to C₃₀ synthesis is not sufficient to make much difference to the overall rate of C₂₉ synthesis. Both results of analysis of wax from whole plants and experiments with tissue slices in vitro indicated that the effect of TCA in reducing the glaucousness of the leaf surface is a combination of overall reduction of wax synthesis together with slight but significant changes in wax composition.