Metabolic origin of acetaldehyde emitted by poplar (Populus tremula x (P. alba) trees |
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Authors: | Kreuzwieser J; Scheerer U; Rennenberg H |
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Institution: | Albert-Ludwigs-Universitat Freiburg; Institut fur Forstbotanik und Baumphysiologie, AM Flughafen 17, D-79085 Freiburg i, Br., Germany; Corresponding author; Fax: +49 761 203 8302; E-mail: kreuzwie@sun2.ruf.uni-freiburg.de |
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Abstract: | The metabolic origin and emission by the leaves of the tropospheric trace
gas acetaldehyde were examined in 4-month-old poplar trees
(Populus tremula x P. alba)
cultivated under controlled environmental conditions in a greenhouse.
Treatments which resulted in increased ethanol concentration of the xylem
sap caused significantly enhanced rates of acetaldehyde and ethanol
emission by the leaves. Leaves fed 14C]-ethanol via
the transpiration stream emitted
<14C]-acetaldehyde. These findings suggest that
acetaldehyde in the leaves is synthesized by a metabolic pathway that
operates in the opposite direction of alcoholic fermentation and results in
oxidation of ethanol. Enzymatic studies showed that this pathway is
mediated either by alcohol dehydrogenase (ADH; EC 1.1.1.1) or catalase
(CAT; EC 1.11.1.6), both constitutively present in the leaves of poplar
trees. Labelling experiments with 14C]-glucose
indicated that the ethanol delivered to the leaves by the transpiration
stream is produced in anaerobic zones of submersed roots by alcoholic
fermentation. Anoxic conditions in the rhizosphere caused by flooding of
the root system resulted in an activation of alcoholic fermentation and led
to significantly increased ethanol concentrations in the xylem sap. These
results support the hypothesis that acetaldehyde emitted by the leaves of
trees is derived from xylem transported ethanol which is synthesized during
alcoholic fermentation in the roots.Keywords:
Acetaldehyde, emission, ethanol, anaerobiosis, Populus
tremula x P. alba
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