Acetaldehyde emission by the leaves of trees - correlation with physiological and environmental parameters

The leaves of trees emit significant amounts of acetaldehyde which is synth esized there by the oxidation of ethanol. In the present study, we examined plant internal and environmental factors controlling the emission of aceta ldehyde by the leaves of young poplar (Populus tremula x P. alba) trees. Th e enzymes possibly involved in the oxidation of ethanol in the leaves of tr ees are catalase (CAT; EC 1.11.1.6) and alcohol dehydrogenase (ADH; EC 1.1. 1.1), both expressed constitutively in the leaves of poplars. Inhibition of ADH in excised leaves caused a significant decrease of acetaldehyde emissi on accompanied by an increased ethanol emission. Since inhibition of CAT by aminotriazole did not affect acetaldehyde and ethanol emission, it is conc luded that the oxidation of ethanol in the leaves is mediated by ADH rather than by CAT. Further studies indicated that aldehyde dehydrogenase (ALDH; EC 1.2.1.5) seems to be responsible for the oxidation of acetaldehyde. The present results demonstrate that acetaldehyde emission is clearly dependent on its production in the leaves as controlled by the delivery of ethanol t o the leaves via the transpiration stream. Environmental factors that contr ol stomatal conductance seem to be of less importance for acetaldehyde emis sion by the leaves.