27
General Overview
organized in blebs scattered throughout the whole chloroplast. The most important storage product is the floridean starch, an α-1,4-glucan polysaccharide, which is deposited in the cytoplasm.
Grains of this starch are located only in the cytoplasm, unlike the starch grains produced in the
Chlorophyta, which lie inside the chloroplasts. Most rhodophytes live photoautotrophically. In
the great majority of red algae, cytokinesis is incomplete. Daughter cells are separated by the pit
connection, a proteinaceous plug that fills the junction between cells; this connection successively
becomes a plug. Species in which sexual reproduction is known generally have an isomorphic or
heteromorphic diplohaplontic life cycle; haplontic life cycle is considered an exception.
The class Bangiophyceae includes all multicellular genera, in which the gametophyte has
chloroplasts lacking a peripheral encircling thylakoid, and the Golgi is associated with both
endoplasmic reticulum (ER) and mitochondrion. Many economically important genera found
in intertidal and subtidal habitats, such as Porphyra purpurea and P. umbilicalis, belong to this
class; they are harvested for human food across the North Atlantic and are under development
as aquaculture crops for human and animal foods. Porphyra species (Figures 1.1c and 1.33) are
important reference red algae because of their multicellularity, high stress tolerance (e.g., to
heat, freezing, high light, osmotic stress, and desiccation), ancient fossil record of the Bangiales,
and capacity to synthesize an array of storage carbohydrates and light-protection compounds.
The life history of Bangiales such as Porphyra spp. involves an alternation between the economically important foliose blade (haploid gametophyte) and the microscopic, filamentous, diploid
conchocelis phase.
The class Compsopogonophyceae includes microscopic filamentous algae (e.g., Erythrocladia;
Figure 1.1d) to macroscopic multicellular species (e.g., Compsopogon). They live in coastal seawater or freshwater. They possess two distinctive ultrastructural characters in combination: the
association of Golgi bodies with ER instead of mitochondria, typical of almost all red algae, and the
presence of a peripheral encircling thylakoid in the chloroplast. The color of chloroplasts is variable
from greenish blue to red. Asexual reproduction occurs by monospores generated by the oblique
division of vegetative cells. Sexual reproduction and alternation of generations are reported in the
Erythropeltidales.
The Cyanidiophyceae are all unicellular, spherical, or elliptical in shape, growing in volcanic
and thermal areas under extremely low pH (0.05–5) and relatively high temperature (35–56°C).
Unlike most eukaryotes, they are also capable of tolerating a large array of toxic chemical compounds such as sulfuric acid, arsenic, and other heavy metals. They reproduce by binary fission
(Cyanidioschyzon; Figure 1.1e) or by formation of endospores (Cyanidium, Galdieria); they can be
facultative heterotrophs or obligate photoautotrophs.
The Florideophyceae (Figures 1.1f and 1.38) includes all multicellular genera, both marine and
freshwater, in which the gametophytes have chloroplasts with a peripheral encircling thylakoid, and
the Golgi is associated with both ER and mitochondrion. The class contains species as seemingly
different as the coralline algae, characterized for the presence of calcite and Botryocladia, known
as sea-grapes, and parasitic taxa. These algae show a triphasic reproduction cycle: an isomorphic
gametophyte and sporophyte generations are separated by the carposporophyte, a very different
sporophyte that emerges from the development of the zygote. In general, carposporophyte is a set of
small filaments that terminate in diploid spores, carpospores. These disperse and germinate to form
the sporophyte. This is generally pseudoparenchymatous and identical to the gametophyte.
The three classes of Porphyridiophyceae (Figure 1.1g), Rhodellophyceae (Figure 1.1h), and
Stylonematophyceae (Figure 1.1i) include the 10 recognized genera of unicellular red algae of
the subphylum Rhodophytina. In the Porphyridiophyceae, the Golgi bodies are invariably associated with ER and a mitochondrion, while in the Rhodellophyceae the Golgi association can be
either with ER or the functionally equivalent outer membrane of the nuclear envelope. The class
Stylonematophyceae also includes pseudofilamentous or filamentous red algae. In the first two
classes, reproduction occurs by cell division, while in the Stylonematophyceae reproduction occurs
by both cell division and monospores.
General Overview
organized in blebs scattered throughout the whole chloroplast. The most important storage product is the floridean starch, an α-1,4-glucan polysaccharide, which is deposited in the cytoplasm.
Grains of this starch are located only in the cytoplasm, unlike the starch grains produced in the
Chlorophyta, which lie inside the chloroplasts. Most rhodophytes live photoautotrophically. In
the great majority of red algae, cytokinesis is incomplete. Daughter cells are separated by the pit
connection, a proteinaceous plug that fills the junction between cells; this connection successively
becomes a plug. Species in which sexual reproduction is known generally have an isomorphic or
heteromorphic diplohaplontic life cycle; haplontic life cycle is considered an exception.
The class Bangiophyceae includes all multicellular genera, in which the gametophyte has
chloroplasts lacking a peripheral encircling thylakoid, and the Golgi is associated with both
endoplasmic reticulum (ER) and mitochondrion. Many economically important genera found
in intertidal and subtidal habitats, such as Porphyra purpurea and P. umbilicalis, belong to this
class; they are harvested for human food across the North Atlantic and are under development
as aquaculture crops for human and animal foods. Porphyra species (Figures 1.1c and 1.33) are
important reference red algae because of their multicellularity, high stress tolerance (e.g., to
heat, freezing, high light, osmotic stress, and desiccation), ancient fossil record of the Bangiales,
and capacity to synthesize an array of storage carbohydrates and light-protection compounds.
The life history of Bangiales such as Porphyra spp. involves an alternation between the economically important foliose blade (haploid gametophyte) and the microscopic, filamentous, diploid
conchocelis phase.
The class Compsopogonophyceae includes microscopic filamentous algae (e.g., Erythrocladia;
Figure 1.1d) to macroscopic multicellular species (e.g., Compsopogon). They live in coastal seawater or freshwater. They possess two distinctive ultrastructural characters in combination: the
association of Golgi bodies with ER instead of mitochondria, typical of almost all red algae, and the
presence of a peripheral encircling thylakoid in the chloroplast. The color of chloroplasts is variable
from greenish blue to red. Asexual reproduction occurs by monospores generated by the oblique
division of vegetative cells. Sexual reproduction and alternation of generations are reported in the
Erythropeltidales.
The Cyanidiophyceae are all unicellular, spherical, or elliptical in shape, growing in volcanic
and thermal areas under extremely low pH (0.05–5) and relatively high temperature (35–56°C).
Unlike most eukaryotes, they are also capable of tolerating a large array of toxic chemical compounds such as sulfuric acid, arsenic, and other heavy metals. They reproduce by binary fission
(Cyanidioschyzon; Figure 1.1e) or by formation of endospores (Cyanidium, Galdieria); they can be
facultative heterotrophs or obligate photoautotrophs.
The Florideophyceae (Figures 1.1f and 1.38) includes all multicellular genera, both marine and
freshwater, in which the gametophytes have chloroplasts with a peripheral encircling thylakoid, and
the Golgi is associated with both ER and mitochondrion. The class contains species as seemingly
different as the coralline algae, characterized for the presence of calcite and Botryocladia, known
as sea-grapes, and parasitic taxa. These algae show a triphasic reproduction cycle: an isomorphic
gametophyte and sporophyte generations are separated by the carposporophyte, a very different
sporophyte that emerges from the development of the zygote. In general, carposporophyte is a set of
small filaments that terminate in diploid spores, carpospores. These disperse and germinate to form
the sporophyte. This is generally pseudoparenchymatous and identical to the gametophyte.
The three classes of Porphyridiophyceae (Figure 1.1g), Rhodellophyceae (Figure 1.1h), and
Stylonematophyceae (Figure 1.1i) include the 10 recognized genera of unicellular red algae of
the subphylum Rhodophytina. In the Porphyridiophyceae, the Golgi bodies are invariably associated with ER and a mitochondrion, while in the Rhodellophyceae the Golgi association can be
either with ER or the functionally equivalent outer membrane of the nuclear envelope. The class
Stylonematophyceae also includes pseudofilamentous or filamentous red algae. In the first two
classes, reproduction occurs by cell division, while in the Stylonematophyceae reproduction occurs
by both cell division and monospores.