Geology Reference
In-Depth Information
Castanea
leaf after the matured leaf has been extracted and saponified
P
1
X
P
2
X
C
1
In
X
X
X
X
X
B
1
O
X
O
O
O
O
O
O
O
O
m/z
85+83
X
X
X
X
X
O
X
X
X
O
X
O
O
O
O
O
O
O
Retention time
Fig. 5.3
Partial ion chromatograms showing the pyrolysis-GC/MS analysis of modern
Castanea
leaf after the matured product has been extracted and saponifi ed. This reveals the recalcitrant
nature of the aliphatic polymer formed after maturation. For key to symbols see Fig.
5.2
.
M/z
85 + 83 mass chromatogram focuses on the distribution of
n
-alkane/alkene homologues
biomolecules (e.g. cutan) are not present in the original leaf tissue, and the observed
aliphatic signal must derive from the generated macromolecular component(s).
Critically, the pyrolysis characteristics of this material are similar to those derived
from naturally occurring recalcitrant leaf fossils (Stankiewicz et al.
1998
; Gupta
et al.
2007
).
The pyrolysates of leaves matured after lipid extraction lacked detectable
n
-alkane/alkene homologues above C
18
(see discussion on cutin below) and
pyrolysates of those matured after extraction and saponification (Fig.
5.2c
;
Table
5.1
) lacked any detectable
n
-alkyl components, including
n
-alkane/
alkene homologues and
n
-alkanoic acids. The pyrolysates did contain the other
compounds present in leaves matured without any pre-treatment. Thus, the
long-chain
n
-alkanes and
n
-alkenes in the pyrolysate of leaf matured without
chemical pre-treatment are derived from organic solvent extractable lipids;
indeed, long-chain
n
-alkyl compounds are major components of epicuticular
waxes (Eglinton and Hamilton
1967
) and include
n
-alkanes,
n
-alkanols,
n
-alkanoic acids and wax esters.
The source of the
n
-alkyl components in leaves matured after extraction (but not
base hydrolysis) must derive from insoluble but hydrolysable precursors. One pos-
ited source is cutin and to test this we analysed tomato cuticle pre-treated with
solvent extraction and acid hydrolysis. Upon maturation, this treated cuticle yielded
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