218 Marine Macro- and Microalgae: An Overview
cell: one flagellum is transversal and lies in a surface groove (cingulum), and the other is longitudinal
and emerges from a ventral furrow (sulcus) (Taylor 1980). The exception to this rule is the family of
protocentroid dinoflagellates (Prorocentraceae), which have their flagellum inserted in a specific region
called periflagellar area (Faust 1990, 1991).
In a combined action, the flagellum provides cells with the necessary propulsion and mobility, which
may be a competitive advantage in obtaining nutrients and harvesting light at different levels in the water
column (Taylor 1987; Lin 2011). Their mechanism of motility allows them to survive in other parts of the
water column, as they are able to move in response to stressful conditions (i.e., turbulence or shear forces,
quick changes in temperature, nutrient limitation, or intense light intensity). It should be emphasized that
this behavior is regulated not only by the aforementioned factors, but also by the cell age (Steidinger
and Baden 1984). The predation and hostile environmental conditions are also handled via production
of dormant or resilient cysts. Most of these microalgae chiefly reproduce by binary fission (asexual
reproduction), but vegetative motile cells can recombine sexually and produce hipnozygotes or resting
cysts that sink to the benthic layers and remain latent therein. When the surroundings become more
auspicious, resting cysts are able to germinate and thrive, thus restarting their life cycle and recolonizing
the water column (Lewis et al. 1999; Bravo and Figueroa 2014).
Compared to normal eukaryotic cytology, dinoflagellate cells exhibit numerous outstanding
features concerning organization of plastids (Zhang et al. 1999; Speckhard 2010), mitochondria (Waller
and Jackson 2009) and genomes (Rizzo 2003; Wisecaver and Hackett 2011). One of the most striking
difference is their unusual nucleus (called dinokaryon), lacking nucleosomes and histones, and a high
chromosomal DNA content, present in a liquid crystalline form (Rill et al. 1989). Dinoflagellates
present the largest genomes of any known organism; their DNA content is estimated to range within
3–250 pg per cell, whereas most eukaryotes contain an average about 0.54 pg DNA per cell (Spector 1984;
Rizzo 2003). In addition, they possess extranuclear spindles where circular and permanently condensed
chromosomes are attached, even during mitosis (Fensome et al. 1995; Wong and Kwok 2005). A large
number of genes is encoded in tandem gene arrays; lack of common eukaryotic transcription sites (e.g.,
TATA box) and other types of post-transcriptional regulation mechanisms (Beam et al. 1984; Hackett et
al. 2004), materialize their unconventional generic organization and regulation of gene expression.
Another distinguishing characteristic is their cell wall cover. The nine major orders (Peridiniales,
Gonyaulacales, Gymnodiniales, Prorocentrales, Suessiales, Dinophysiales, Phytodiniales, Blastodiniales,
and Noctilucales), recognized within the dinoflagellate group, can be distinguished in terms of major
morphological features and life cycles by referring to their membrane (Not et al. 2012). They may be
naked, or covered with cellulose (or other polysaccharide) plates or valves, or create a sort of armor
named theca (Fensome et al. 1999; Hackett et al. 2004). Theca has a variety of shapes, arrangements,
and sizes, depending on species and cell life stage—thus conferring a more rigid and inflexible wall. The
naked or unarmored forms have an outer plasmalemma, surrounded by a single layer of flattened vesicles
(amphiesma)—apparently easy to distort (Wong and Kwok 2005). Although all dinoflagellates share
certain physiological and structural characteristics, they display a surprising miscellany of forms in terms
of external morphology. Some cells are small and smoothly spherical, whereas others have elaborated
structures such as horn and spikes (Fensome et al. 1999).
Photosynthetic species may possess plastids (i.e., chloroplasts), probably incorporated by secondary
or tertiary endosymbiosis (Cavalier-Smith et al. 1999; Yoon et al. 2002). Acquisition, loss, and replacement
of such organelles are quite common, and may depend on their life cycle. They are also able to harbor
those foreign plastids by a long period of time, but not in a fully integrated way (Steidinger and Baden
1984).
Another trait characterizing dinoflagellates relates to their slow proliferation among unicellular
algae—generally believed to be an attribute related to their low chlorophyll to carbon ratio (Tang
1996). Theoretically, dinoflagellates express a type II ribulose-1,5-bisphosphatecarboxylase-oxygenase
(Rubisco) enzyme, probably originating from anaerobic proteobacteria, yet this enzyme is known to
poorly discriminate between CO 2 and O 2 (Wong and Kwok 2005). This support the idea that Rubisco may
contribute in general to the very low growth rates at stake, while other carbon concentration mechanisms
are implicated in CO 2 biofixation of dinoflagellates (Rost et al. 2006).
cell: one flagellum is transversal and lies in a surface groove (cingulum), and the other is longitudinal
and emerges from a ventral furrow (sulcus) (Taylor 1980). The exception to this rule is the family of
protocentroid dinoflagellates (Prorocentraceae), which have their flagellum inserted in a specific region
called periflagellar area (Faust 1990, 1991).
In a combined action, the flagellum provides cells with the necessary propulsion and mobility, which
may be a competitive advantage in obtaining nutrients and harvesting light at different levels in the water
column (Taylor 1987; Lin 2011). Their mechanism of motility allows them to survive in other parts of the
water column, as they are able to move in response to stressful conditions (i.e., turbulence or shear forces,
quick changes in temperature, nutrient limitation, or intense light intensity). It should be emphasized that
this behavior is regulated not only by the aforementioned factors, but also by the cell age (Steidinger
and Baden 1984). The predation and hostile environmental conditions are also handled via production
of dormant or resilient cysts. Most of these microalgae chiefly reproduce by binary fission (asexual
reproduction), but vegetative motile cells can recombine sexually and produce hipnozygotes or resting
cysts that sink to the benthic layers and remain latent therein. When the surroundings become more
auspicious, resting cysts are able to germinate and thrive, thus restarting their life cycle and recolonizing
the water column (Lewis et al. 1999; Bravo and Figueroa 2014).
Compared to normal eukaryotic cytology, dinoflagellate cells exhibit numerous outstanding
features concerning organization of plastids (Zhang et al. 1999; Speckhard 2010), mitochondria (Waller
and Jackson 2009) and genomes (Rizzo 2003; Wisecaver and Hackett 2011). One of the most striking
difference is their unusual nucleus (called dinokaryon), lacking nucleosomes and histones, and a high
chromosomal DNA content, present in a liquid crystalline form (Rill et al. 1989). Dinoflagellates
present the largest genomes of any known organism; their DNA content is estimated to range within
3–250 pg per cell, whereas most eukaryotes contain an average about 0.54 pg DNA per cell (Spector 1984;
Rizzo 2003). In addition, they possess extranuclear spindles where circular and permanently condensed
chromosomes are attached, even during mitosis (Fensome et al. 1995; Wong and Kwok 2005). A large
number of genes is encoded in tandem gene arrays; lack of common eukaryotic transcription sites (e.g.,
TATA box) and other types of post-transcriptional regulation mechanisms (Beam et al. 1984; Hackett et
al. 2004), materialize their unconventional generic organization and regulation of gene expression.
Another distinguishing characteristic is their cell wall cover. The nine major orders (Peridiniales,
Gonyaulacales, Gymnodiniales, Prorocentrales, Suessiales, Dinophysiales, Phytodiniales, Blastodiniales,
and Noctilucales), recognized within the dinoflagellate group, can be distinguished in terms of major
morphological features and life cycles by referring to their membrane (Not et al. 2012). They may be
naked, or covered with cellulose (or other polysaccharide) plates or valves, or create a sort of armor
named theca (Fensome et al. 1999; Hackett et al. 2004). Theca has a variety of shapes, arrangements,
and sizes, depending on species and cell life stage—thus conferring a more rigid and inflexible wall. The
naked or unarmored forms have an outer plasmalemma, surrounded by a single layer of flattened vesicles
(amphiesma)—apparently easy to distort (Wong and Kwok 2005). Although all dinoflagellates share
certain physiological and structural characteristics, they display a surprising miscellany of forms in terms
of external morphology. Some cells are small and smoothly spherical, whereas others have elaborated
structures such as horn and spikes (Fensome et al. 1999).
Photosynthetic species may possess plastids (i.e., chloroplasts), probably incorporated by secondary
or tertiary endosymbiosis (Cavalier-Smith et al. 1999; Yoon et al. 2002). Acquisition, loss, and replacement
of such organelles are quite common, and may depend on their life cycle. They are also able to harbor
those foreign plastids by a long period of time, but not in a fully integrated way (Steidinger and Baden
1984).
Another trait characterizing dinoflagellates relates to their slow proliferation among unicellular
algae—generally believed to be an attribute related to their low chlorophyll to carbon ratio (Tang
1996). Theoretically, dinoflagellates express a type II ribulose-1,5-bisphosphatecarboxylase-oxygenase
(Rubisco) enzyme, probably originating from anaerobic proteobacteria, yet this enzyme is known to
poorly discriminate between CO 2 and O 2 (Wong and Kwok 2005). This support the idea that Rubisco may
contribute in general to the very low growth rates at stake, while other carbon concentration mechanisms
are implicated in CO 2 biofixation of dinoflagellates (Rost et al. 2006).