Genetic control of β-diketone and hydroxy-β-diketone synthesis in epicuticular waxes of barley.

Five eceriferum, (cer) mutants in barley which influence β-diketone and hydroxy-β-diketone synthesis in spike and internode epicuticular waxes have been characterized. The mutation cer-u (69) blocks the synthesis of hydroxy-β-diketones and leads to a compensatory increase in the amount of β-diketones, indicating that β-diketones are precursors of the hydroxy-β-diketones. Furthermore, highly lobed wax plates were observed for the first time on barley lemmas, in addition to the characteristic wax tubes. Both diketone classes are selectively and proportionally reduced in the spike wax of cer-i (16), which has shorter wax tubes. The three mutants cer-c (36), -q (42), and -c,u (108) synthesize neither diketone class and form no wax tubes. In contrast to the variable composition of most individual barley wax classes, only a single β-diketone was identified, namely hentriacontan-14,16-dione.