Molecular Decay of Plant Biopolymers - Biopolymers: A Molecular Paleontology Approach - page 5

Fig. 1.1 Total ion chromatogram from Py-GC-MS of modern Metasequoia glyptostroboides after
lipid extraction (sample 1), and at various stages of natural decay (samples 4-6). Ps: polysaccha-
ride derivative; P: phenol; Bn: alkyl phenol; Pn: alkyl phenols, where n denotes number of carbons
in the alkyl component; Vp: vinyl phenol, G denotes guaiacyl lignin units ( G1 2- methoxy phenol,
G2 2-methoxy-4-methyl phenol, G3 4-ethenyl-2-methoxyphenol; G5 3-allyl-6-methoxyphenol);
Lv Levoglucosan; C 16:2 FA C 16 diunsaturated fatty acid, C16FA saturated fatty acid
Figure 1.2 highlights the molecular species of interest in this study: the mass
chromatograms showing the distribution of the pyrolysis products of vinyl phenol vs.
lignin (Fig. 1.2a ) and vinyl phenol vs. cellulose (Fig. 1.2b ), respectively. Clearly, the
guaiacyl lignin units in sample 1 (undecayed) decrease progressively in abundance to
vinyl phenol (through sample 4-6, Fig. 1.2a ); a trend observed in levoglucosan derived
from cellulose when compared to vinyl phenol (Fig. 1.2b ). Vinyl phenol may be pro-
duced by thermal breakdown of the p -hydroxyphenol unit in certain types of lignin as
a part of woody tissue, but in leaves it is mainly related to p -coumaric acid. It is pres-
ent both as ester- and ether-linked units in woody tissues (as part of lignin), and also
as part of decay-resistant cuticle (Tegelaar et al. 1989 ). Vinyl phenol (4-ethenyl phe-
nol) is produced, along with C 16 unsaturated fatty acids as the primary thermal break-
down product during pyrolysis of cutin (Tegelaar et al. 1989 ) and isolated cuticles
(Mösle et al. 1998 ) and is derived from p -coumaric acid as part of decay-resistant
cuticle (Tegelaar et al. 1989 ). For these reasons, changes in the chemical composition
of the leaves have been determined by the abundance of specifi c moieties relative to
that of vinyl phenol. Vinyl phenol has been used as a marker for cutin and cuticle in