The effects of dry O-3, SO2 and NO2 on reconstituted epicuticular wax tubules

Epicuticular wax tubules were reconstituted in vitro by recrystallizing nonacosan-10-ol from the soluble cuticular lipids of Picea pungens Engelm. on a glass support. Fumigation of these preparations for 100 h with dry O-3 (1.8%), SO2 (100%) or for 1500 h with NO2 (0.1%) did not change their composition or crystal habit. Exposure of reconstituted wax tubules to 1% of dry NO2 yielded planar crystals of nonacosan-10-one after 100 h. Further exposure (264 h) resulted in the complete degradation of aggregates and the formation of nonadecanoic and eicosanoic acids. The same oxidation steps and the accompanying changes of crystal shapes could be induced by fumigation of nonacosan-10-ol tubules with 100% of dry NO2 for 0.25-1 h and for 2 h, respectively. The oxidation of nonacosan-10-ol depended on the doses applied. At ambient concentrations, equivalent doses would accumulate only over thousands of years. Oxidative transformations alone can therefore not account for the in vivo degradation of wax tubules on conifer needles.