Distribution of Cutan in Modern Leaves - Biopolymers: A Molecular Paleontology Approach - page 22

Pyrolysis products were separated using a DB-1 fused silica capillary column
(30 m, 0.25 mm i.d., 0.1 m fi lm thickness) to evaluate the distribution of pyrolysis

products of leaf tissue (Gupta and Pancost 2004 ), especially the n - alkyl component
(for greater insight into the polar (non-aliphatic) compounds see Ralph and Hatfi eld
1991 ). The GC oven was programmed from 40 (held for 4 min) to 320 °C at
5 °C min −1 and held at that temperature for 15 min. Helium was the carrier gas. The
MS was operated at 70 eV scanning over the range m/z 45-600 at 1 scan s −1 with an
emission current of 300

μ

A (full scan mode). Two to three replicate samples were
analysed to check the consistency of the runs. Compounds were identifi ed using the
NIST mass spectral library and from published spectra (Ralph and Hatfi eld 1991 ;
Bland et al. 1998 ).

μ

Analytical Results

The pyrolysis-GC/MS profi le of Agave americana after solvent extraction (Residue 1)
revealed a dominance of n -alkane and n -alk-1-ene homologues ranging in carbon
number from C 8 to C 35 and maximising at C 28 (Fig. 2.2a ), indicating the presence of a
dominant n- alkyl component, which is characteristic of Agave americana (Tegelaar
et al. 1991 ). Phenols and polysaccharide pyrolysis products are also present. Fatty acyl
components were detected in relatively low abundance, as the Agave cuticle tissue was
sampled from a fully developed, mature part of the plant where the ratio between cutin
and cutan is relatively low; the proportion of cutin is greater in immature parts of the
plant (Tegelaar et al. 1991 ). The pyrolysis-GC/MS profi les of Residue 2 (after saponi-
fi cation/base hydrolysis, Fig. 2.2b ) and Residue 3 (after acid and base hydrolysis,
Fig. 2.2c ) show the persistence of n -alkane/alk-1-ene homologues including those with
carbon chain length >C 20 . These n -alkene/alkanes indicate the presence of cutan, con-
sistent with results from a number of other studies (Nip et al. 1986a , b ; Tegelaar et al.
1989c , 1991 ; McKinney et al. 1996 ; Mösle et al. 1997 ; Villena et al. 1999 ).
The pyrolysate of the angiosperm Prunus laurocerasus after extraction contains
components related to polysaccharides, lignin and cutin, i.e., saturated and unsatu-
rated C 16 and C 18 fatty acyl moieties (Fig. 2.3a : for details on the molecular structure
and chemical formula of these compounds see Ralph and Hatfi eld 1991 ; van Bergen
1999 ). Also present is an n -alkyl component represented by n -alkane/alk-1-ene
homologues ranging up to n -C 32 ; n -alkane/alk-1-ene homologues from n -C 26 to 31
are the most abundant. Inset Fig. 2.3a shows the distribution of the n -alkanes and
n -alkenes separately to show more clearly the n- alkyl building components. As with
Agave , the pyrolysate of Residue 2 from Prunus laurocerasus contains n -alkane/
alk-1-ene homologues, including long chain homologues (Fig. 2.3b ). The pyrolysate
of post saponifi cation Residue 2 of Clivia miniata also contains n -alkane/alk-1- ene
homologues (data not shown) and a similar residue remains following acid hydrolysis
(see also Villena et al. 1999 ).
In striking contrast, in all other leaves analysed, although n -alkane/alk-1-ene
homologues are present in the pyrolysate of the extracted leaves (Residue 1), they