Biology Reference
In-Depth Information
presence of lignin in algae has never been previously reported. Calliarthron
is a coralline alga exposed to strong waves and presents calcified fronds.
This alga has some joints called genicula where lignin has been discovered.
Lignin presence has been related to the need to prevent the breakage
caused by waves (although the tiny quantity makes this role questionable).
The presence of a secondary cell wall, with a pattern analogous to that of
secondary cell wall formation in angiosperms, has also been described.
Derivatization followed by reductive cleavage (DFRC) showed the pres-
ence of the three monolignols, in a proportion that varied depending on
the season, age or development stage, which has previously been observed
in some other species (
Christiernin, 2006b
). The ratio H:G:S varied from
1:1.5:trace to trace:1:1, but pointed to the occurrence of syringyl lignin in a
red algae that diverged from vascular plants more than one billion years
ago (
Saunders and Hommersand, 2004
). Although the presence of lignins
is validated in these samples, its origin remains unclear and finding the
genes that support monolignol synthesis are still under investigation.
Ligrone et al. (2008)
also reported the occurrence of lignin (or lignin-like
compounds) in the charophycean alga Nitella flexilis, using immunocyto-
chemical analysis. However, the labelling intensity was very weak against
guaiacyl lignin-like polymers but surprisingly, though still weak, stronger
against guaiacyl/syringyl lignin. Moreover, the labelling was uniformly
distributed in the cell walls.
Sørensen et al. (2011)
determined the composition of the cell walls in
charophycean green algae, ancestors of the first land plants (
Graham,
1996
), more specifically, Coleochaete nitellarum, Coleochaete orbicularis and
Coleochaete scutata cell walls released guaiacyl and syringyl monomers when
subjected to thioacidolysis (
Fig. 4
). Coleochaete represents a group of char-
ophycean green algae, with cell walls comparable to embryophyte primary
cell walls. The total amount of monomers was very low in the three species,
but the lignin or lignin-like nature of the released compounds was also
confirmed by the use of immunocytochemical analyses. Anti-lignin antibo-
dies labelled cell walls in all three Coleochaete species, suggesting that some
sort of phenylpropanoid metabolism emerged before land colonization.
Sørensen's results differ from Ligrone's, who reported no reaction with
antibodies against lignin in the alga C. scutata.
B. EMBRYOPHYTES (LAND PLANTS)
Land plants are also called embryophytes because they have a resting embryo
stage early in the life of the sporophyte. The embryophytes descended from a
charophyte-like ancestor and possess three important new features: alternation
