25th International Meeting on Organic Geochemistry IMOG 2011

O-32
The role of light intensity in controlling the �D and � 13 C values of
organic compounds in leaf waxes: Should we worry about it?
Nikolai Pedentchouk 1 , Kirill Peskov 2 , Tracy Lawson 3 , Yvette Eley 1
1 The University of East Anglia, Norwich, United Kingdom, 2 Institute for Systems Biology SPb, Moscow,
Russian Federation, 3 The University of Essex, Colchester, United Kingdom (corresponding
author:n.pedentchouk@uea.ac.uk)
Several recent studies have suggested that a
simultaneous analysis of � 13 C and �D of n-alkyl
biomarkers in leaf waxes may help identify the type of
vegetation contributing to the sedimentary record. The
rationale behind this approach is that in C3 plants the
� 13 C and �D are linked because of their dependence
on water use efficiency (WUE) [1]. Here we show that
the assumption about this link might not necessarily
be correct, because during biosynthesis �D of lipids
could also be influenced by other factors that are
decoupled from those controlling the � 13 C values.
We measured � 13 C and �D of leaf wax n-alkanes
from 4 lines of Arabidopsis thaliana grown indoors.
The plants were subjected to 3 light treatments, while
the rest of parameters (duration of illumination,
temperature, relative humidity, and water) were kept
constant. In addition, we measured leaf water �D,
transpiration, CO2 conductance, net photosynthesis,
as well as chlorophyll concentration and fluorescence.
The isotope and gas flux data were then used to
develop a kinetic model to estimate �D of NADPH.
As expected, the plants differed in their
physiological response to various light treatments.
WUE was considerably greater in high (HL) than in
middle (ML) and in low (LL) lights. We found that � 13 C
of n-C31 alkane are consistent with the differences in
WUE among the plants at 3 light levels. However, our
data also showed that �D of n-C31 in HL are more
negative than in ML and LL, which, unlike � 13 C in ML
and LL, almost totally overlap (Fig.1). Furthermore,
the pattern among �D of n-C31 at 3 light levels is
different from that shown by the transpiration data.
Our kinetic model, which includes the effects of
light sensitive enzyme-driven processes, allowed us
to estimate��D of NADPH at 3 light levels. We found
that the pattern among �D of NADPH is similar to nalkane
�D and dissimilar to transpiration.
The results of this work suggest that light intensity
is an important environmental parameter that
significantly influences both � 13 C and �D of leaf
waxes. However, �D is decoupled from � 13 C because
of the different biochemical mechanisms affecting D/H
and 13 C/ 12 C fractionations during photosynthesis.
Fig. 1. �D values of n-C31 alkane (measured) and NADPH
(modelled), and transpiration measured for 4 different lines
of Arabidopsis thaliana at 3 light levels. D/H fractionation
between H2O and NADPH equal to � = 0.40 [2] was used
during model simulations for calculating the resultant �D of
NADPH at each of 3 light levels.
References
[1] Hou, J. et al. (2007) Org. Geochem. 38, 1251-1255.
[2] Luo, Y.-H. et al. (1991) Plant Cell Physiol. 32, 897-900.
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