Verlag des Forschungszentrums Jülich
JUEL-3622
· Absolute emission rates vary for different vegetative stages.
· Despite these differences in absolute emission rates the dependencies of the
emission rates on temperature and light intensity can be described independent
of the vegetative state with the same set of parameters using the algorithm of
SCHUH ET AL. (1997). Just the standard emission rates are dependent on the
vegetative state.
· Emissions of monoterpenes from rape are limited by the availability of DMAPP.
This limitation is independent on the vegetative state and therefore, a description
of emissions with the same set of parameters is possible.
· Exposure of rape plants with high amounts of ozone (130-170 ppb O3) leads to
reduced emissions of monoterpenes that can be explained by a reduced DMAPP
availability.
· The underlying model idea of the algorithm of SCHUH ET AL. (1997) that monoterpenes
are emitted from two independent mechanisms was confirmed by isotopic measurements.
The model idea was extended to isoprene.
· Mechanical wounding results in increased emissions of monoterpenes from sunflower
and tomato.
· As a result of nitrate deficiency monoterpene emissions are increased for rape
and sunflower. For sunflower an exponential increase of emission rates on a time
scale of hundred to several hundred hours was found.
· Emissions of sesquiterpenes that are synthesized by the same biochemical pathway
as isoprene and monoterpenes cannot be described by the algorithm of
SCHUH ET AL. (1997). Theses compounds are effective phytoalexins. They are actively
produced by the plants after action of stress factors (stressors) on the plants.
Therefore, the sesquiterpene emissions show a time dependency that cannot be
described by the algorithm of SCHUH ET AL. (1997).
Emissions of compounds resulting from LOX activity were quantified for the first
time. It was found that:
· Beside the well-known emissions of C6-alcohols and -aldehydes several other
compounds are emitted during LOX activity.
· The emissions resulting from LOX activity are qualitatively very similar for
tobacco, corn, sunflower, broad beans and pine. Probably the same emissions occur
generally from higher plants.
· Differences in the composition of emissions from different plant species can be
explained through different activities of alcohol dehydrogenases (ADH) in different
species.
· The composition of emissions resulting from LOX activity in tobacco is similar
for different stress factors like ozone fumigation and pathogen attack. This gives
further evidence to the hypothesis that the exposure with ozone resembles pathogen
attack in triggering the hypersensitive response (e.g. SANDERMANN ET AL., 1998).
· The amount of VOCs that are emitted as a result of LOX activity can be comparable
to the VOC amount emitted under stress free conditions over the whole vegetative
period.
· The dynamics of LOX activity were examined by measurements of the delay time of
emissions of several compounds.
· Compared to the uptake of atmospheric peroxides the amount of peroxides that are
produced inside the plants resulting from LOX activity is by far higher.
Emissions of aromatic compounds by plants that are considered unlikely up to now,
have been identified. It was shown that:
· Regarding the amounts, methyl salicylate (MeSA) is the most important emitted
aromatic compound. Under stress conditions emissions of MeSA can be as high as those
of monoterpenes.
· Besides MeSA emissions, emissions of other aromatic compounds from the shikimate
pathway were found. Some of these compounds may be regarded as precursors of MeSA.
· Emissions of compounds produced by the shikimate pathway are always found after a
hypersensitive response occurred, but a hypersensitive response is not a necessary
requirement for emissions of those compounds.
· Steady state emissions of MeSA can appear, if stress factors act on plants on
longer time scales. In these cases the light intensity dependence of the MeSA
emissions can be described by the algorithm of SCHUH ET AL. (1997).
It was shown that compounds like toluene and C6- to C10-alkanales are emitted by
plants. The biosynthetical pathway for these compounds is not known. It was found
that:
· Emission rates of toluene from sunflower are highly correlated with a-pinene
emissions. They are dependent on light intensity, temperature, nitrate availability
and wounding.
· The aromatic ring of toluene is synthesized within few hours from the CO2 fixed
in photosynthesis.
· Under stress conditions emission rates of C6- to C10-alkanales from agricultural
plant species may be as high as those of monoterpenes.
· An algorithm for the description of emissions of C6- to C10-alkanales as a
function of the ozone flux into the plants and the temperature was developed.
VOC emissions from agricultural plant species are much lower than those from
pines. Especially the VOC emissions from wheat plants are that low that areas
cultivated with wheat can be neglected in biogenic VOC emission inventories as
long as no stress factors are applied to the plants.
Heiden, Arnd Christian; Kobel, Klaus; Wildt, Jürgen
Einfluß verschiedener Streßfaktoren auf die Emission pflanzlicher flüchtiger organischer Verbindungen
314 S., 1999
Emissions of Volatile Organic Compounds (VOCs) from several biosynthetic pathways
were investigated. Beside the well-known emissions of terpenes, that are synthesized
from dimethylallyl pyrophosphate (DMAPP), emissions following lipoxygenase (LOX)
activity or from the shikimate pathway were found. Furthermore, it was shown that
several VOCs like toluene and C6- to C10-aldehydes, where no biosynthetical pathway
is known, are emitted by plants.
For monoterpene emissions it was shown that:
· For sunflower direct or indirect toluene pools have to be postulated.
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