and unicellular species: Zygnematophyceae. Finally,
Prasinophyceae,
Chlorophyceae,
Trebouxiophyceae,
Mesostigmatophyceae, Chlorokybophyceae, and Chaetosphaeridiophyceae are only unicellular.
The cell wall of Viridiplantae (Chlorobionta and
Streptobionta) is characterized by a wide variety of chemical
compounds, which are often present simultaneously in
the same taxon. It can comprise (i) cellulose, a glucose
unbranched polymer with glycosidic β-1,4 bonds and with
hydrogen bonds between neighbor chains, holding the chains
firmly together side-by-side, (ii) mannane, a polymer of mannose, (iii) xylane, a polymer of xylose, (iv) hemicelluloses,
polymers of galactose, or mannose close to the cellulose,
(v) pectin, a polymer of α-1,4 galacturonic acid
9 (with carboxyl groups often esterified with methanol) with some α-1,2
rhamnose, (vi) and lignin, a very complex branched polymer
of phenylpropanoids. The cellulose, though present in
other eukaryotic taxa, and the lignin, characteristic of the
Streptobionta,
10 are emblematic chemical compounds of
the Viridiplantae. These two compounds, which are mainly
(cellulose) or totally (lignin) synthesized by Viridiplantae,
account for the major part of the Earth biomass, respectively
50 % and 30 % (Raven et al. 2000; Boerjan et al. 2003; Evert
and Eichhorn 2013).
Chloroplasts of the Viridiplantae have a two-layer envelope. Thylakoids are stacked in lamellae (up to 30 thylakoids
per lamella). There are two types of thylakoids, a unique
feature in eukaryotes (Fig. 7.18): long thylakoids (also called
intergranal thylakoids) and short thylakoid (granal
thylakoids). Photosystem I and ATP synthase are mostly
located in the long thylakoids, whereas Photosystem II is
located mostly in the short thylakoids. In Chlorobionta, the
stacks of short thylakoids are rather irregular in length; they
are called pseudograna (cf. Chap. 5, Fig. 5.13). In contrast,
in Streptobionta, stacks of short thylakoids are clear-cut;
they are called grana. Two types of Chlorophyll are
usually present simultaneously: chlorophyll a and b. A
third type of chlorophyll, chlorophyll c, is present in some
Prasinophyceae (Rodriguez et al. 2005; Six et al. 2005). The
carotenoid pigments are represented by carotenes α and β
and many xanthophylls: antheraxanthin, prasinoxanthin,
siphonaxanthin, siphonein, violaxanthin, zeaxanthin, etc.
Xanthophylls are less abundant than chlorophyll and therefore do not mask their color. The main storage polysaccharide is the starch (“true starch”), a mixture of amylose and
amylopectin; amylose is an unbranched glucose polymer
with α-1,4 bonds; amylopectin is a branched glucose polymer with α-1,4 and a few α-1,6 bonds (every 24–30 glucose
units). Starch is stored within the chloroplasts, not in
the cytoplasm, a unique feature among photosynthetic
eukaryotes (Fig. 7.18). Plastids specialized in the storage
of starch (amyloplasts) can be present in Steptobionta and
Prasinophyceae
Chlorophyceae
Trebouxiophyceae
Ulvophyceae
Cladophorophyceae
Bryopsidophyceae
Dasycladophyceae
Trentepohliophyceae
Chlorokybophyceae
Klebsormidiophyceae
Zygnematophyceae
Chaetosphaeridiophyceae
Charophyceae
Coleochaetophyceae
Rhodobionta (outgroup)
Bryophyta (lato sensu)
Filicophyta (lato sensu)
Magnoliophyta (lato sensu)
Embryophyta
Chlorobionta
Streptobionta
The customary
concept of
‘green algae’, a
paraphyletic
group deprived
of meaning
(see text)
Mesostigmatophyceae
Fig. 7.17 Phylogenetic tree of
Viridiplantae. The outgroup
(Rhodobionta) is in red. This tree
is a summary of the trees
proposed by Hoek et al. (1998),
Lecointre and Le Guyader (2006),
Brodie et al. (2007) and Leliaert
et al. (2012). Embryophyta,
which are always multicellular,
are not presented in detail. The
Magnoliophyta encompass the
flowering plants, the Filicophyta
the ferns, and the Bryophyta the
mosses
9 Uronic acids (e.g. the galacturonic acid) are a class of sugar acids
(hexoses) with both carbonyl and carboxylic acid functional groups. In
the case of pectin, the hexose is galactose.
10 Apart from Streptobionta, lignin is also present in a species of
Rhodobionta living in the intertidal zone. According to Martone et al.
(2009), the lignin biosynthetic pathways may have been present in the
common unicellular ancestor of Viridiplantae and Rhodobionta.
212
C.-F. Boudouresque
Prasinophyceae,
Chlorophyceae,
Trebouxiophyceae,
Mesostigmatophyceae, Chlorokybophyceae, and Chaetosphaeridiophyceae are only unicellular.
The cell wall of Viridiplantae (Chlorobionta and
Streptobionta) is characterized by a wide variety of chemical
compounds, which are often present simultaneously in
the same taxon. It can comprise (i) cellulose, a glucose
unbranched polymer with glycosidic β-1,4 bonds and with
hydrogen bonds between neighbor chains, holding the chains
firmly together side-by-side, (ii) mannane, a polymer of mannose, (iii) xylane, a polymer of xylose, (iv) hemicelluloses,
polymers of galactose, or mannose close to the cellulose,
(v) pectin, a polymer of α-1,4 galacturonic acid
9 (with carboxyl groups often esterified with methanol) with some α-1,2
rhamnose, (vi) and lignin, a very complex branched polymer
of phenylpropanoids. The cellulose, though present in
other eukaryotic taxa, and the lignin, characteristic of the
Streptobionta,
10 are emblematic chemical compounds of
the Viridiplantae. These two compounds, which are mainly
(cellulose) or totally (lignin) synthesized by Viridiplantae,
account for the major part of the Earth biomass, respectively
50 % and 30 % (Raven et al. 2000; Boerjan et al. 2003; Evert
and Eichhorn 2013).
Chloroplasts of the Viridiplantae have a two-layer envelope. Thylakoids are stacked in lamellae (up to 30 thylakoids
per lamella). There are two types of thylakoids, a unique
feature in eukaryotes (Fig. 7.18): long thylakoids (also called
intergranal thylakoids) and short thylakoid (granal
thylakoids). Photosystem I and ATP synthase are mostly
located in the long thylakoids, whereas Photosystem II is
located mostly in the short thylakoids. In Chlorobionta, the
stacks of short thylakoids are rather irregular in length; they
are called pseudograna (cf. Chap. 5, Fig. 5.13). In contrast,
in Streptobionta, stacks of short thylakoids are clear-cut;
they are called grana. Two types of Chlorophyll are
usually present simultaneously: chlorophyll a and b. A
third type of chlorophyll, chlorophyll c, is present in some
Prasinophyceae (Rodriguez et al. 2005; Six et al. 2005). The
carotenoid pigments are represented by carotenes α and β
and many xanthophylls: antheraxanthin, prasinoxanthin,
siphonaxanthin, siphonein, violaxanthin, zeaxanthin, etc.
Xanthophylls are less abundant than chlorophyll and therefore do not mask their color. The main storage polysaccharide is the starch (“true starch”), a mixture of amylose and
amylopectin; amylose is an unbranched glucose polymer
with α-1,4 bonds; amylopectin is a branched glucose polymer with α-1,4 and a few α-1,6 bonds (every 24–30 glucose
units). Starch is stored within the chloroplasts, not in
the cytoplasm, a unique feature among photosynthetic
eukaryotes (Fig. 7.18). Plastids specialized in the storage
of starch (amyloplasts) can be present in Steptobionta and
Prasinophyceae
Chlorophyceae
Trebouxiophyceae
Ulvophyceae
Cladophorophyceae
Bryopsidophyceae
Dasycladophyceae
Trentepohliophyceae
Chlorokybophyceae
Klebsormidiophyceae
Zygnematophyceae
Chaetosphaeridiophyceae
Charophyceae
Coleochaetophyceae
Rhodobionta (outgroup)
Bryophyta (lato sensu)
Filicophyta (lato sensu)
Magnoliophyta (lato sensu)
Embryophyta
Chlorobionta
Streptobionta
The customary
concept of
‘green algae’, a
paraphyletic
group deprived
of meaning
(see text)
Mesostigmatophyceae
Fig. 7.17 Phylogenetic tree of
Viridiplantae. The outgroup
(Rhodobionta) is in red. This tree
is a summary of the trees
proposed by Hoek et al. (1998),
Lecointre and Le Guyader (2006),
Brodie et al. (2007) and Leliaert
et al. (2012). Embryophyta,
which are always multicellular,
are not presented in detail. The
Magnoliophyta encompass the
flowering plants, the Filicophyta
the ferns, and the Bryophyta the
mosses
9 Uronic acids (e.g. the galacturonic acid) are a class of sugar acids
(hexoses) with both carbonyl and carboxylic acid functional groups. In
the case of pectin, the hexose is galactose.
10 Apart from Streptobionta, lignin is also present in a species of
Rhodobionta living in the intertidal zone. According to Martone et al.
(2009), the lignin biosynthetic pathways may have been present in the
common unicellular ancestor of Viridiplantae and Rhodobionta.
212
C.-F. Boudouresque