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Ochrophytes are algae of diverse organization and
include unicellular, colonial, filamentous and
parenchematous thalli.
They are characterized by the presence of chlorophylls
a and c in their plastids as well as xanthophylls (e.g.
fucoxanthin) and other carotenoids that mask the
chlorophylls (Table 2).
Due to the presence of these pigments, many
ochrophytes have a yellowish-green, gold or brown
appearance.
As storage products, they accumulate oils and
chrysolaminarin (C) in cytoplasmic vesicles, but never
starch.
Cell walls contain cellulose, and in certain species they
contain silica.
Cells possess one or more plastids, each with an
envelope formed by two membranes of chloroplast and
two membranes of chloroplast endoplasmic reticulum.
Thylacoids, in stacks of three, in most ochrophytes are
surrounded by a band of thylakoids, girdle lamella, just
beneath the innermost plastid membrane.
Ochrophytes have heterokont flagellated cells with two
different flagella, an anterior tinsel (mastigonemes) and
posterior whiplash (smooth) flagellum (Fig. ).
In this group of algae, mastigonemes consist of three
parts, a basal, tubular and apical part formed by fibrils.
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Heterokontophyta
(Ochrophyta)
Fig. Semidiagrammatic drawing of a light
and electron microscopical view of the
basic organization of a cell of the
Chrysophyceae. (C) Chrysolaminarin
vesicle; (CE) chloroplast envelope;
(CER) chloroplast endoplasmic
reticulum; (CV) contractile vacuole; (E)
eyespot; (FS) flagellar swelling; (G) Golgi
body; (H) hair of the anterior flagellum;
(MB) muciferous body; (MR)
microtubular root of flagellum; (N)
nucleus.
Chrysophyceae and related groups
• Chrysophyceans (Golden-brown algae) are mostly unicellular
flagellate organisms.
• Some are amoeboid or coccoid.
• Most of the species in the Chrysophyceae are freshwater, occur in
unpolluted and soft waters (low in calcium).
• Some are strictly marine algae and part of the nanoplankton.
• Some have a single functional flagellum like Chromulina, while others
can form colonies like the freshwater genus Uroglena.
Chromulina
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The chloroplasts are parietal and
usually only a few in number, often
only one or two.
Chlorophylls a, c1, and c2 are
present, with the main carotenoid
being fucoxanthin which give them a
golden color.
The chloroplasts are surrounded by
two membranes of chloroplast E.R.,
the outer membrane of which is
usually continuous with the outer
membrane of the nuclear envelope.
The thylakoids are usually grouped
three to a band.
Pyrenoids are common in
chloroplasts of the Chrysophyceae.
The storage product is
chrysolaminarin (leucosin), a β1,3 linked glucan, supposedly found
in a posterior vesicle (C).
Contractile vacuoles in the anterior
portion of the cell (CV).
Uroglena
Semidiagrammatic drawing of a light and electron
microscopical view of the basic organization of a cell of
the Chrysophyceae. (C) Chrysolaminarin vesicle; (CE)
chloroplast envelope; (CER) chloroplast endoplasmic
reticulum; (CV) contractile vacuole; (E) eyespot; (FS)
flagellar swelling; (G) Golgi body; (H) hair of the
anterior flagellum; (MB) muciferous body; (MR)
microtubular root of flagellum; (N) nucleus.
The following classes are commonly recognized in this division and will
be discussed here:
1. Chrysophyceae (golden-brown algae)
2. Synurophyceae
3. Eustigmatophyceae
4. Pinguiophyceae
5. Dictyochophyceae (silicoflagellates)
6. Pelagophyceae
7. Bolidophyceae
8. Bacillariophyceae (diatoms)
9. Raphidophyceae (chloromonads)
10.Xanthophyceae (yellow-green algae)
11.Phaeothamniophyceae
12.Phaeophyceae (brown algae)
• Phylogenetic analysis using rDNA nucleotide sequences of the 16S
subunit have shown that the classes Chrysophyceae, Synurophyceae,
Eustigmatophyceae, Raphidophyceae, Pelagophyceae and
Dictyochophyceae are evolutionarily close. Phaeophyceae,
Xanthophyceae, Phaeothamniophyceae, Pinguiophyceae and
Chrysomerophyceae are also related, and Bacillariophyceae and
Bolidophyceae form an isolated group.
• Many of the Chrysophyceae have a
tinsel flagellum that is inserted at the
anterior end of the cell parallel to the
cell axis and a whiplash flagellum that
is inserted approximately perpendicular
to the tinsel flagellum.
• The posterior whiplash flagellum is
usually the shorter flagellum and has a
swelling at its base on the side toward
the cell contains an electron-dense
area referred to as the photoreceptor.
• The flagellar swelling fits into a
depression of the cell immediately
beneath which, inside the chloroplast,
is the eyespot.
• The eyespot consists of lipid globules
inside the anterior portion of the
chloroplast, between the chloroplast
envelope and the first band of
Semidiagrammatic drawing of a light and electron
thylakoids.
microscopical view of the basic organization of a cell of
the Chrysophyceae. (C) Chrysolaminarin vesicle; (CE)
chloroplast envelope; (CER) chloroplast endoplasmic
reticulum; (CV) contractile vacuole; (E) eyespot; (FS)
flagellar swelling; (G) Golgi body; (H) hair of the
anterior flagellum; (MB) muciferous body; (MR)
microtubular root of flagellum; (N) nucleus.
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Most of the Chrysophyceae are sensitive to changes in the environment and
survive the unfavorable periods as statospores.
The formation of a cyst or statospore or resting spore is one character by
which a member of the Chrysophyceae or Synurophyceae may be recognized.
Statospores, are shaped like a small, externally ornamented bottle enclosed in a
silicified wall with a terminal pore closed by nonsilicified plug (P).
A vegetative cell forms a statospore internally.
• The presence of cellulose in cell walls is common, and some species
are covered with scales or protected by an organic sheath called the
lorica (L), an envelope around the protoplast, but not generally
attached to the protoplast as a wall is.
• Scales (if they are present) are made of silica and are radially or
biradially symmetrical
• Very few chrysophyceans are naked.
When a statospore germinates,
there is a dissolution of the plug or
separation of it from the spore
wall. The protoplast then moves
out of the statospore by amoeboid
motion, forming flagella as it
moves out.
Formation of a statospore or cyst
in Ochromonas tuberculata. (a)–
(c) The formation of the
statospore. (d) A mature
statospore as seen from the collar
end. (C) Chloroplast; (Co) collar of
statospore; (Cr) chrysolaminarin
vesicle; (CV) contractile vacuole;
(D) discobolocyst; (N) nucleus; (P)
plug in pore of statospore; (S)
statospore wall; (SDV) silica
deposition vesicle; (Sp) spine.
Chrysococcus rufescens. (a) Whole cell. (b) Cell
undergoing reproduction. (c) Ultrastructure of
vegetative cell. (B) Branched cytoplasmic process; (E)
eyespot; (G) Golgi; (L) lorica; (LV) leucosin vesicle; (LF)
long flagellum; (N) nucleus; (SF) short flagellum; (V)
contractile vacuole.
Statospore of Ochromonas sphaerocystis.
• Nutrition in the Chrysophyceae can be either phototrophic,
phagotrophic, or mixotrophic (photosynthetic organism capable of
taking up particles and molecules from the medium).
• Food particles include both living (bacteria, small algae, or even
cells of its own kind) and non-living (detritus, fecal material).
• The mixotrophic chrysophytes, Epipyxis pulchra have the ability to
select or reject specific food item.
Phagotrophy in Epipyxia pulchra. The cell has a posterior stalk by which it is attached to a lorica. (a)
The long tinsel flagellum beats in such a way that water and suspended particles are drawn to the
cell. (b) A particle is seized by the long tinsel flagellum. (c) The particle is maneuvered between the
two flagella. (d) A feeding cap from the cell envelopes the particle. (e) The particle is enclosed within
a food vacuole within the cytoplasm. The stalk has pulled the cell into the lorica.
• Chrysophytes are notorious for their production of fishy or rancid
smells, reflecting release of unsaturated aldehydes derived from the
high cell content of polyunsaturated acids.
• These chemicals are classified as algal volatile organic
compounds (AVOCs).
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Two different types of projectiles occur in the
Chrysophyceae, muciferous bodies and
discobolocysts.
On discharge the contents of the vesicle in
muciferous bodies (MB) often form a fibrous network
outside the cell.
The discobolocysts (D) are in the outer layer of
cytoplasm and consist of a single membrane
bounded vesicle with a hollow disc in the outward
facing part of the vesicles. The discharge is
explosive, taking place by the expansion of the
projectile into a thin thread 6 to 11 µm long.
Semidiagrammatic drawing of a light and electron
microscopical view of the basic organization of a cell of
the Chrysophyceae. (MB) muciferous body.
(a) Ochromonas tuberculatus. (D) discobolocyst; (b)
Charged and discharged discobolocysts.
• Mitotic division is the most
common mechanism of
asexual reproduction.
• Sexual reproduction is rare,
but when it occurs, gametes
are anisogamous.
• Vegetative cells are haploid,
and meiosis is the first
division of the zygote.
• In some cases, zygotes are
statospores, representing a
resting phase.
Three unsaturated fatty-acid derivatives produced by
chrysophytes that result in rancid or fishy odors.
The life cycle of Dinobryon.
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• Eustimatophytes are yellow-green unicells that
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occur in freshwater, brackish water, and seawater as
well as in the soil.
They produce naked zoospores.
Most bear a single pleuronematic (mastigonemes )
flagellum, but some have two flagella.
They are characterized by the presence of a large
orange red extraplastidial (outside the chloroplast)
stigma.
Other characteristics of the class include a basal
swelling of the tinsel flagellum (FS) adjacent to the
eyespot, only chlorophyll a, chloroplasts without girdle
lamellae and no peripheral ring of DNA, and
chloroplast endoplasmic reticulum not connected to
the nuclear envelope.
The chloroplasts of the Eustigmatophyceae have βcarotene and two major xanthophylls, violaxanthin and
vaucheriaxanthin. Violaxanthin is the major lightharvesting pigment in the Eustigmatophyceae
• Synurophyceae are flagellate algae
covered with silica-scales (S).
They are closely related to the Chrysophyceae.
The Synurophyceae differ from chrysophyceans in
the following: the Synurophyceae lack chlorophyll
c2, the flagella are inserted into the cell
approximately parallel to one another (Fig. ), there
is a photoreceptor (P) near the base of each
flagellum, there is no eyespot, the contractile
vacuole (CV) is in the posterior portion of the cell
and the loss of the ability to carry out phagocytosis.
Biflagellate unicellular forms can live in colonies.
Of the 200 species that compose this group, most
of them belong to the cosmopolitan genera
Mallomonas and Synura.
Sexual reproduction occurs by isogamy, vegetative
cells are haploid, and zygotes may remain as cysts
when environmental conditions are unfavorable.
ٍAs they inhabit relatively unpolluted freshwater,
they are good indicators of water quality.
Several members of the Synurophyceae thrive in
acidic lakes. As environmental concerns over the
acidification of lakes by acid rains increase, these Semidiagrammatic drawing of the cytology of
Synura, showing the characteristic cytology of
species will probably be more widely used as
the Synurophyceae. (CV) Contractile vacuole;
indicators of lake acidification.
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(a) Diagrammatic representation of the basic
morphology of a zoospore of the Eustigmatophyceae.
(C) Chloroplast; (CER) chloroplast endoplasmic
reticulum; (E) eyespot; (F) long flagellum; (FB) basal
body of short flagellum; (FS) flagellar swelling; (LV)
lamellate vesicles; (N) nucleus.
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The life cycle of Chattonella
antiqua involves a vegetative
propagation phase and a nonmotile dormant phase.
The vegetative diploid cells grow
by binary fission under normal
growth conditions.
Small haploid cells are produced
when the nutrients are depleted
in the medium.
These haploid cells change into
cysts under low-light conditions
and spend several months
dormant in bottom sediments.
The period of dormancy usually
lasts from the end of summer to
the following spring and is
enforced by low temperatures.
Swarmers germinate from the
cysts and somehow become
diploid, although how
diploidization occurs is not
known.
The resulting diploid vegetative
cells complete the life history.
(F) flagella; (G) Golgi; (L) chrysolaminarin
vesicle; (N) nucleus; (P) photoreceptor; (S)
scale; (SV) scale vesicle.
• Raphidophyceae are unicellular flagellate algae, also known as
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The life cycle of Chattonella antiqua.
Chloromonads.
The anterior flagellum is commonly tinsel, whereas the posterior flagellum is
naked.
Their plastids contain chlorophylls a and c, and two membranes of chloroplast
endoplasmic reticulum.
Unlike other ochrophytes, the endoplasmic reticulum membrane that envelops
the chloroplast is not connected to the membrane surrounding the nucleus.
The cells have trichocysts like in dinoflagellates.
There are about 15 species, most of which are marine algae.
The freshwater species of the Raphidophyceae
are green, whereas the marine forms are
Chattonella antiqua
yellowish and contain the carotenoid fucoxanthin.
Many of the marine species produce neurotoxic
compounds that are similar to brevetoxin.
Uptake of the toxin by fish results in
depolarization of nerves supplying the heart.
This reduces the heart rate, thereby lowering
blood pressure, which in turn affects the transfer
of oxygen to the gill lamellae, creating hypoxic
conditions that lead to fish mortality.
Toxic red-tide blooms of the marine Chattonella
antiqua and Heterosigma carterae have
reported in Japan. In 1972, a bloom of C.
antiqua killed 500 million dollars worth of caged
yellow-tail fish in the Seto Inland Sea in Japan (a) Heterosigma carterae. (b) Fibrocapsa japonica.
(C) Chloroplast; (M) mucocyst.
Bacillariophyceae
• Bacillariophyceans, or diatoms, constitute the largest class of
Ochrophyta.
• About 10,000 benthic and planktonic species are known, and they
can be found in both freshwater and marine environments.
• This group is responsible for 25% of primary production of the sea.
• Diatoms are unicellular, and in some cases, live in colonies with a
filamentous appearance, formed by numerous loosely-joined
individuals.
Some common diatoms that might occur in your field samples. (1) Chaetoceros sp.; (2)
Thalassiothrix sp.; (3) Skeletonema costatum; (4) Coscinodiscus sp.; (5) Nitzschia sp.; (6)
Eucampia sp.; (7) Rhizosolenia sp; (8) Thalassiosira gravida; (9) Nitzschia pungens, chain.
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The frustule is composed of two overlapping halves, the smaller fitting into the
larger like a Petri dish
The outer half is the epitheca and the inner the hypotheca.
Each theca is composed of two parts, the valve, a more or less flattened plate,
and the connecting band, attached to the edge of the valve. The two connecting
bands, one attached to each valve, are called the girdle or cingulum.
Occasionally there are one or more additional bands.
• The most distinctive feature of diatoms is their rigid translucent wall,
or frustule, consisting of silicon dioxide (SiO2) and traces of other
substances, such as aluminum, magnesium, iron and titanium.
• The inorganic component of the frustule is enveloped by an organic
component or “skin”, the latter composed of amino acids and sugars
with the amino acid hydroxyproline, uronic acid and collagen
present.
• Cellulose is never present.
• In discussing diatoms and silica, there is often confusion over
terminology in regard to silicon.
– Silicon is the element.
– Silica is a short convenient designation for silicon dioxide
(SiO2) in all of its crystalline, amorphous, and hydrated or
hydroxylated forms.
– Silicate is any of the ionized forms of monosilicic acid [Si(OH)4]
Semidiagrammatic representation of a cell of Melosira varians composed of two valves, V
and V, two girdle band series: 1, 2, 3, and, underlapping these, the younger series 1, 2, 3.
• The use of scanning microscopy has
revealed the complexity of frustule
structures.
• The siliceous material of the frustule
is laid down in certain regular
patterns that leave the wall
ornamented.
• The ornamentation of the frustule is
very complex and each species has
a configuration of specific spines,
pores or striae.
• When looking at the frustule from the top or bottom, the
faces of the diatom can be seen in a valvar view, while
from the side, a girdle or cingular view can be observed.
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Diatoms can be classified in four basic groups based on the ornamentation of
diatoms :
(1) centric and radial, where the structure is arranged according to a central
point (Fig. a)
(2) trellisoid, where the structure is arranged uniformly over the surface without
reference to a point or line (Fig. b)
(3) gonoid, where the structure is dominated by angles (Fig. c);
(4) pennate, where the structure is symmetrically arranged upon either side of
a central line (Fig. d)
The basic patterns of ornamentation in the Bacillariophyceae. (a) Centric and radial (example
Coscinodiscus). (b) Trellisoid, with structure arranged margin to margin (example Eunotia). (c) Gonoid,
with structure supported by angles (example Triceratium). (d) Pennate, symmetrical about an apical line
(example Navicula).
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Besides the raphe, there are basically two types of wall perforations within
the Bacillariophyceae:
the simple pore or hole,
and the more complex chambers known as loculi (singular loculus or
areola) (Figs. 17.6, 17.12)
The structure of the valve wall with loculi resembles a honeycomb.
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Fig. 17.6 The types of openings in frustule walls. (a) Hole or pore (Chaetoceros didymos var.
anglica). (b) Loculus opening outward (Coscinodiscus linatus). (c) Loculus opening inward
(Thalassiosira wailesii). (h) Hole; (lp) lateral pore or pass pore; (sm) sieve membrane; (sp)
sieve pore.
• The valve surface can have extensions, called
processes, whose main function appears to be to
maintain contact between contiguous cells and to assist
colony formation.
• These processes are given different names:
Some pennate diatoms have a raphe
system composed of the raphe (r) (a
longitudinal slot in the theca), divided into
two parts by the central nodule (cn).
Each half of the raphe terminates in a
swelling of the wall called the polar
nodule (pn).
The ornamentation in the pennate diatoms
is bilaterally symmetrical around the
raphe.
In those pennate diatom valves that do not
have a raphe system, there is instead an
unornamented area running down the
center of the valve, which is called the
pseudoraphe.
Diatoms with only one or two raphes are
able to move due to the production of a
mucilaginous material that flows out of the
raphe and holds the cell to the substrate.
The contraction of this material and the
production of new mucilage cause a
sliding movement of the cell.
(a) A cell with a raphe system (Pinnularia viridis).
(cn) Central nodule; (pn) polar nodule; (r) raphe. (b) A
cell with a pseudoraphe (pr)
• Pores or loculi (punctae) in a single row are referred to as stria
(plural striae).
– Cornuate processes are horn-like;
– strutted processes are ones that have been reduced to a boss
at the apex of a valve;
– spinulae are very small processes;
– awns or setae are hollow and elongated.
• Asexual reproduction occurs by bipartition.
• When mitosis occurs, the two valves are separated and each
produces a new hypotheca, so that the hypotheca of the parental
cell always acts as the epitheca of the daughter cells.
• After successive cell divisions over time, there is an effect on the
average cell size of the diatom population.
• This phenomenon has been observed in natural populations.
• The mean diameter of the population progressively decreased until
a minimum mean diameter was reached, at which point cell size
suddenly increased due to the formation of spores called
auxospores.
• Auxospores were generally the result of sexual reproduction
processes, but in some cases they were produced asexually.
Fig. 17.4 Climaconeis colemaniae. Light and scanning electron micrographs of the frustule. The valve
contains linear striae, each with 6–8 poroid aerolae. The valve contains a raphe opening. Two pores
occur in the area of the central nodule.
• Special pores (mucilage or slime pores)
through which mucilage is secreted are known
in many diatoms. In the pennate diatoms,
these pores usually occur singly near one or
both poles of the valve and generally occupy
thickenings in the walls.
• The protoplasm is located inside the frustule; in their plastids thylakoids
form packs of three surrounded by the girdle lamella.
• Photosynthetic pigments are chlorophylls a and c (c1, and c2), as well as
the carotenoids fucoxanthin (giving the cells their golden-brown color),
diatoxanthin and violaxanthin.
• The most common storage products are chrysolaminarin and lipids.
• Diatoms contain unique 4α-methyl sterols, such as 4-desmethylsterol and
cholesterol.
Light microscopical drawing of valve (a) and girdle (b) views
of the diatom Mastogloia. (c) Drawing of a transverse
section of M. grevillei in the transmission electron
microscope. (Ch) Chloroplast; (CN) central nodule; (E)
elongate chamber of a septum; (GB) girdle band; (I)
intercalary band; (IBE) intercalary band of the epitheca;
(IBH) intercalary band of the hypotheca; (LT) locule
tubule;(O) oil; (R) raphe; (S) stria.
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Extracellular mucilage
• Diatoms produce five types of mucilaginous aggregation:
• (1) tubes,
• (2) pads,
• (3) stalks,
• (4) fibrils,and
• (5) adhering films
• A substantial part of the carbon fixed by benthic diatoms is secreted
as extracellular mucilages
• Sexual reproduction of diatoms is rare in nature and usually occurs as
described before.
• The life cycle is diplontic with isogamy in pennate diatoms (both
gametes are non flagellated) and
oogamy in centric diatoms (the male gamete is motile, whereas the
female gamete (egg) is nonmotile).
• In some cases, auxospore formation is a consequence of selfing: the
fusion of two haploid nuclei produced by the same diploid cell.
• Auxospore formation can also be caused by changes in
environmental conditions of temperature, light and available nutrients.
• Sexual reproduction in diatoms can occur only after two general
conditions have been met.
– First, cells must reach a minimum size range, typically 30–40% of their
maximum size.
– Second, there must be the presence of correct environmental conditions.
These include combinations of temperature, light, nutrients, trace metals,
organic growth factors, and osmolarity.
• Contrary to most other algal groups, sexuality is primarily a means of
size restoration, and is not normally a factor in dormancy or dispersal
Forms of extracellular mucilage in diatoms.
Motility
• Some diatoms are able to glide over the surface of a substrate.
Gliding is restricted to those pennate diatoms with a raphe
(described previously) and those centric diatoms with labiate
processes (L).
• Nearly all motile diatoms must adhere to
the substratum in the area of their raphe in
order for movement to occur.
• The labiate processes have a pore in the
center, and the mucilage is secreted
through the pore.
• Diatoms can glide only when the valve containing a raphe is in
contact with the surface. If the diatom cell settles with the girdle
contacting the substrate, the diatom secretes a mucilaginous tether
from the portion of the raphe near the central nodule. The tether
attaches to the substratum and the cell pulls itself onto a valve
containing a raphe using the tether.
(b) A cell that has settled on the girdle bands. Tether
mucilage is secreted from the raphes of each valve.
The tether mucilage is attached to the substrate. (c)
Tether mucilage extending from the raphe in the
central nodule area to the substrate.
Resting spores and resting cells
• Some diatom cells form thick, ornamented walls at different times in
their life cycle and become resting spores. If such cells are
planktonic, they fall to the bottom where, presumably, they await
more favorable conditions.
• Resting cells have the same morphology as vegetative cells and do
not form a protective layer, thereby differing from resting spores.
Biolfouling
• Diatoms are ubiquitous fouling microorganisms, attaching to
submerged structures by secreting insoluble mucilages. Achnanthes
longipes is a common marine fouling diatom that is highly resistant
to toxic antifouling coatings. It produces a stalk that elevates it
above the toxic coatings on ship bottoms. Fouling of ship bottoms
increases the frictional drag, leading to excess fuel consumption.
Cleaning ship hulls coasts millions of dollars each year, leading to
an additional loss of revenue.
Fig. 17.17 Scanning electron micrographs of Achnanthes longipes. (a) Whole cell showing the pad, shaft,
and collar of the mucilaginous stalk. Also shown is a path of mucilage left by the gliding diatom and
surface film (SF) of mucilage left on the substratum. (b) The attachment of the collar (C) of the stalk (Sh)
on the cell. (R) Raphe. (c) The attachment of the pad to the substratum.
• Diatoms that are attached to a substrate and
are motile on the substrate have the advantages of
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(a), (b) Ditylum brightwelli. (a) Vegetative cell. (b) Resting spore. (c), (d) Amphora
coffaeformis. Drawings of the ultrastructure of a vegetative cell (c) and a resting cell (d).
(C) Chloroplast; (L) lipid; (N) nucleus; (V) vacuole.
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(1) being held in position in moving water;
(2) avoiding burial by moving up and over sediments;
(3) moving to colonize vacant areas; and
(4) moving to areas with more light and/or nutrients
Rhythmic phenomena
• It is possible to synchronize the division of diatom cells in
a culture in a couple of different ways.
– Removal of silicon from cultures of Navicula pelliculosa stops
growth of the cells at a stage prior to cytokinesis. When silica is
added to the culture, all of the cells then divide synchronously.
– Another way of obtaining synchronized cell divisions is by
keeping the diatoms in the dark for a long period followed by
exposure to light. In Nitzschia palea the shortest time that can be
obtained between cell divisions is 16 hours. If the cells are grown
on an 8 hour light : 8 hour dark cycle, synchronously dividing
cells are obtained. If the cycle is shortened to 6 hours light : 6
hours dark, then cell division occurs every second dark period
because there is insufficient time for the diatom to prepare itself
for the next division.
• Auxospore formation is a
second mechanism (in addition
to resting spores) for
reestablishing the original size of
the cell. The auxospores are
formed by the fusion of two
gametes.
• Depending on the species,
auxospores develop in one of
three different ways
• 1 Isodiametric auxospores.
Centric diatoms such as Melosira
• 2 Properizonial auxospores.
Centric diatoms such as
Chaetoceros produce nonisodiametric (non-spherical)
mature auxospores.
• 3 Perizonial auxospores.
Pennate diatoms such as
Navicula form this type of nonisodiametric mature auxospore
Diagrammatic summary of the three types of sexual
auxospores in diatoms.
• The effects of heavy metals on diatoms can be
divided into three groups:
– (1) Cu, Zi, and Ge affect the biochemical pathway of
silicon metabolism;
– (2) Hg, Cd, and Pb interfere with cell division and
cause morphologically distorted cells to be produced;
and
– (3) Cr, Ni, Se, and Sb (Antimony) have no effects up
to a concentration of 1 µM, well above the
concentrations that show effects with other toxic
metals.
Physiological issues
• Silicon cannot be replaced by any of the elements similar to it in
physical and chemical properties or in atomic radius, such as Ge, C,
Sn, Pb, As, P, B, Al, Mg, or Fe.
• Concentrations of germanium dioxide (GeO2) above 1.5 mg liter1
will specifically suppress the growth of diatoms. The finding that
GeO2 specifically inhibits diatom growth was a welcome one for
phycologists working on algal cultures.
• In addition to responding adversely to germanium in solution,
diatoms are sensitive to copper. Concentrations of 0.25 ppm copper
as CuSO4.5H2O are normally used to control algal blooms without
affecting fish in freshwater lakes.
Amnesic shellfish poisoning occurs when shellfish filter diatoms from
the genera Nitzschia, Pseudo-nitzschia, and Amphora from marine
waters.
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Nitzschia
Pseudo-nitzschia
• Subsequent ingestion of the shellfish by
man and birds results in memory loss
(amnesia), abdominal cramps, vomiting,
disorientation, and even death.
• The diatom produces domoic acid, a
derivative of the neuroexcitatory amino
acid L-glutamic acid.
• Domoic acid is especially prevalent in
moribund cells of the diatom and can be
induced by depriving the cells of
nutrients, particularly silicate and
phosphate.
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Amphora
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Some normally photosynthetic diatoms are able to grow under heterotrophic
conditions with glucose as the sole carbon source.
When the organism is growing in the light, it does not have the mechanism
for the utilization of glucose in the medium. It requires about 24 hours in the
dark in a glucose medium before it is able to use the glucose as a carbon
source. This lag period indicates that the lack of light induces an uptake
and/or assimilation system for the glucose.
It was suggested that such facultative heterotrophy enables these diatoms
to settle into bottom deposits, live heterotrophically for long periods, then
rise and begin photosynthesis again.
Although the above diatoms still have functional chloroplasts, there are
some colorless apochlorotic diatoms lacking functional chloroplasts.
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Species of Nitzschia, are able to grow with lactate or succinate as the sole
organic carbon source.
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In nature, some Apochlorotic diatoms live on decaying marine vegetation
and the mucilages of large seaweeds
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Diatoms cells contain large quantities of highly unsaturated fatty acids such
as eicosanoic acid (Fig. a) in vesicles in the cytoplasm.
Death of cells during feeding by invertebrates results in the release of the
unsaturated fatty acids into the seawater which convert into the unsaturated
short-chain aldehydes 2,4-decadienal and 2,4,7-decatrienal (Fig. b).
These short chain fatty-acid aldehydes are toxic to developmental stages of
a range of invertebrates including copepods, sea urchins, polychaetes, and
ascidians, reducing the numbers of the next generation of these grazers.
Future generations of grazers are sabotaged, encouraging the survivability
of diatom populations.
Interestingly, the released aldehydes also are toxic to diatoms. However,
the diatoms cells are being destroyed by the grazing and are already out of
the gene pool.
Chemical defense against predation
• Diatoms are preferred food for invertebrates such as copepods.
Some diatoms (e.g., Phaeodactylum tricornutum, Skeletonema
pseudocostatum) have evolved a mechanism to reduce predation by
releasing chemicals that reduces the fecundity of the next
generations of invertebrates.
(a) The reaction by which a non-toxic highly unsaturated fatty acid is converted by a phospholipase into a
reactive unsaturated fatty-acid aldehyde that is toxic to invertebrates. The reaction is initiated by wounding
of the diatom cell. (b) Two unsaturated fatty-acid aldehydes, decatrienal and decadienal, that are toxic to
invertebrates and a saturated fatty-acid aldehyde, tridecanal, that is not toxic.
Phaeodactylum tricornutum
Spring diatom increase
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Skeletonema
Some ecological aspects
The spring diatom bloom is a strong increase in phytoplankton abundance
(especially the diatoms) that typically occurs in the early spring and lasts until
late spring or early summer.
This seasonal event is characteristic of temperate North Atlantic, sub-polar,
and coastal waters.
The magnitude, spatial extent and duration of a bloom depends on a variety of
environmental conditions, such as light availability, nutrients, temperature, and
stratification of the water column.
• Diatoms comprise the main component of the open-water marine
flora and a significant part of the freshwater flora.
• In the marine environment the colder the water is, the greater the
diatom population.
• The maintenance of oceanic diatoms in the water column involves
some adaptation of the cells to make them buoyant.
• Adaptations of large and heavy cells (large diatoms) to reduce
sinking, and to maintain near neutral buoyancy and vertical position
in the euphotic zone, include
– chain formation and cell extensions that provide a high surface area:
volume ratio. Cell extensions increase frictional drag and also increase
the effective size of phytoplankton cells, which makes them more
difficult for zooplankton grazers to capture and ingest.
– production of gas vacuoles and the accumulation of fats and oils, which
are lighter than water.
• Cell aging and nutritional state of phytoplankton cells are
physiological conditions that affect cell density. Post-bloom nutrientstarved diatoms tend to sink significantly faster than nutrient-rich
diatoms.
Idealized diagram tracing changes in phyto-plankton, zooplankton, light, and nutrients during the year in a
temperate-boreal inshore body of water.
Fossil diatoms
• The siliceous frustules of diatoms have been well preserved in the
fossil record.
• Diatomaceous fossil deposits, known as diatomaceous earth or
diatomite, are exploited in many parts of the world and have
important industrial applications as abrasives, refractory ceramic
and filters.
• The industrial uses of diatomaceous earth are varied.
– One of the first uses was as a mild abrasive in toothpaste and metal
polishes.
– Diatomaceous earth was also used as an absorbent for liquid
nitroglycerin to make dynamite that could be transported with
comparative safety. The inert medium used in the present-day
manufacture of dynamite is wood meal.
– Probably the most extensive industrial use of diatomaceous earth is in
the filtration of liquids, especially those of sugar refineries.
– Another major use is in the insulation of boilers, blast furnaces, and
other places where a high temperature is maintained.
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Spring diatom increase mechanism
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During winter, wind-driven turbulence (often derived from storms) and cooling water
temperatures break down the stratified water column formed during the summer.
This breakdown allows vertical mixing of the column.
This mixing replenishes nutrients from depth to the surface waters and the rest of the
euphotic zone.
In winter, phytoplankton use these nutrients to perform photosynthesis. However,
vertical mixing also causes high losses, as phytoplankton are carried below the euphotic
zone (so their respiration exceeds primary production). In addition, reduced illumination
(intensity and daily duration) during winter limits growth rates.
In the spring, more light becomes available and stratification of the water column
occurs as increasing temperatures warming the surface waters (referred to as thermal
stratification). As a result, vertical mixing is inhibited and phytoplankton and nutrients
are held at the surface. This coupling of nutrients and phytoplankton promotes
exponential increases in photosynthetic activity, and, thus, spring bloom.
Spring blooms typically last until late spring or early summer, at which time the bloom
collapses due to nutrient depletion in the stratified water column and increased grazing
pressure by zooplankton.
Phytoplankton die or are ingested and egested by zooplankton, sinking below to great
depths. Because of the stabilization of the water column, these materials and other
nutrients are not returned to the surface from the bottom.
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The onset of relatively quiet summer conditions further stabilizes the water column.
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Toward the end of summer, with the advent of fall storms, the thermocline may be
disrupted, bringing some nutrients toward the surface from the bottom in shallow water.
This may result in a fall increase of phytoplankton.
• The systematic arrangement of diatoms has traditionally been based
on morphology and consists of a single class called Bacillariophyceae.
• The Bacillariophyceae can be divided into two orders as follows:
Order 1 Biddulphiales (Centrales): radial (centric) or gonoid
ornamentation; many chloroplasts; no raphe; resting spores formed;
motile spermatozoids with a single tinsel flagellum; oogamous sexual
reproduction.
Order 2 Bacillariales (Pennales): pennate or trellisoid ornamentation;
one or two chloroplasts; raphes possibly present with gliding; no
flagellated spermatozoids; sexual reproduction by conjugation.
• Common genera include Nitzschia, Pseudo-nitzschia, Navicula,
Amphora, Cymbella, and Pinnularia
– Melosira, a common golden-brown diatom found in marine and freshwater
environments, consists of cylindrical cells with a greater length than
Breadth
– Chaetoceros has more than 160 species, the largest number of any
planktonic diatom. The genus is widespread in warm and cold waters.
Nitzschia palea
Amphora
Pseudo-nitzschia
Cymbella
Navicula
Melosira granulata
Pinnularia
Chaetoceros
Dictyochophyceae
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These golden-brown algae are characterized by tentacles or rhizopodia on
basically amoeboid vegetative cells.
• Amoeboid cells are relatively rare among the algae, being mostly restricted
to the Dictyochophyceae and the Xanthophyceae.
Classification: The Dictyochophyceae can be divided into three orders:
• Order 1 Rhizochromulinales: marine and freshwater unicells with tentacles.
• Rhizochromulina has amoeboid non-flagellated vegetative cells with many
fine beaded-filipodia and fusiform zoospore has a single tinsel flagellum
• Order 2 Pedinellales: unicells with a long anterior flagellum and a second
flagellum reduced to a basal body. Their body is covered with scales,
usually three to six chloroplasts (if chloroplasts are present) are located in a
ring surrounding the nucleus, which occupies a central position. Some
species are capable of emitting pseudopodia and catch small organic
particles, marine and freshwater.
Rhizochromulina marina. Vegetative cell (a) and
zoospore (b).
a) Pedinella hexacostata in the light and electron
microscope. (c) Apedinella spinifera
PELAGOPHYCEAE
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• http://www.microscopyview.com/
• http://cfb.unh.edu/phycokey/phycokey.htm
• http://blackseaeducation.ru/phytoplankton.shtml
• http://www.microscopyview.com/MENU/40
0-DIATOM/406-MID/H406-7700.html
The Pelagophyceae are a group of basically
unicellular algae that are cytologically similar to the
Chrysophyceae
The cells are very small (3–5 µm) members of the
ultraplankton and appear as small spheres with
indistinct protoplasm under the light microscope.
Members of the class are economically important
because some of the algae produce “brown tides.”
Aureoumbra lagunensis is the causative agent of
brown tides in Texas. Aureoumbra lagunensis is able
to grow at its maximum rate at salinities as high as
70 PSU (practical salinity units; seawater is about 35
PSU). Few algae are able to survive these
hypersaline conditions. In addition, the surface of the
cells are covered with a slime layer that reduces
predation. A combination of these advantages
enables A. lagunensis to outcompete other algae.
Aureococcus anophagefferens forms brown tides along the coasts of New
Jersey, New York, and Rhode Island. The numbers of cells in brown tides
can be so large that they can exclude light from the benthic eelgrass
(Zostera marine), resulting in elimination of the eelgrass. The larvae of the
bay scallop feed off eelgrass and the bay scallop industry was virtually
wiped out for a number of years after a brown tide in the waters off the
northeast United States.
A. anophagefferens is a psychrophilic alga that is able to grow at low
temperatures and survive extended periods of darkness. This explains its
ability to form algal blooms.
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Order 3 Dictyocales: or silicoflagellates are a group of cosmopolitan marine
(constitute a prominent part of the phytoplankton in the cold seas) unicells
flagellates (have one emergent flagellum) with a silicified skeleton and represented
by only one extant genus Dictyocha.
The cytoplasm surrounds the skeleton and contains golden discoid plastids.
In Dictyocha speculum, the skeleton-bearing cells multiply vegetatively by mitotic
division. Cells connected by bridges develop and give rise to large spherical cells
without skeletons that become multinucleate. Uninucleate swarmers with a single
flagellum develop in the large spherical cells. The swarmers are released and grow
into large multinucleatecells, which are probably a form of resting cell. All of the
cells are of the same ploidy level and sexual reproduction is not known.
fine structure of Dictyocha
fibula. (b), (c) Side and
front views of the skeleton
of Dictyocha. (ar) Apical
ring; (br) basal ring; (c)
chloroplast; (cb) cell
boundary; (m)
itochondrion; (n) nucleus;
(p) pseudopodium; (rs)
radial spine; (s) silica
skeleton; (sb) supporting
bar.
Growth stages of the silicoflagellate Dictyocha
speculum.
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Flagellate cells have two lateral or apical
insertion heterokont flagella with a
forwardly directed tinsel flagellum and a
posteriorly directed whiplash flagellum.
The eyespot (E) in motile cells is always in
the chloroplast, and the chloroplasts are
surrounded by two membranes of
chloroplast endoplasmic reticulum. The
outer membrane of the chloroplast E.R. is
usually continuous with the outer
membrane of the nucleus.
In most non-motile cells the wall is
composed of two overlapping halves that fit
together as do the two parts of the
bacteriologist’s Petri dish.
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Xanthophyceae and related groups
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The organization of xanthophyceans, or Tribophyceae,
varies from simple filaments to amoeboid cells to siphonous thalli.
The chloroplasts contain chlorophylls a and c, lack fucoxanthin, and are
colored yellowish-green.
As storage products, they accumulate chrysolaminarin, paramilo (β-1,3
linked glucan similar to paramylon), sugars and oils.
Their cell walls contain cellulose and often silica scales.
Sexual reproduction is only known in three genera with a haplontic life cycle.
Some species form resistant cysts with silica walls, closed by a cap.
Xanthophyceans, despite their green color, can be distinguished from
chlorophytes by their lack of chlorophyll b and by their heterokont flagella.
Most of the 600 known xanthophyceans species live in freshwater and moist
soil, and only a few are marine species.
The freshwater and marine genus Vaucheria has a cylindrical body
consisting of a branched coenocytic filament with many discoid plastids and
numerous nuclei.
Light and electron microscopical drawing of a zoospore
of a typical member of the Xanthophyceae,
Mischococcus sphaerocephalus. (C) Chloroplast; (CV)
contractile vacuole; (E) eyespot; (FS) flagellar swelling;
(LF) long flagellum with hairs; (N) nucleus; (SF) short
flagellum; (V) vacuole.
Vaucheria coronata, coenocytic filament and Oogonium
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The heterotrichous genera Giraudyopsis and Chrysomeris belong to the
class Chrysomerophyceae, characterized by a lack of alginates.
The class Phaeothamniophyceae includes freshwater filamentous
forms, which can be simple or branched, without chrysolaminarin.
They produce biflagellate zoospores as in Phaeothamnion.
This class is most closely related to the Xanthophyceae and Phaeophyceae
and the cytology of these three classes is similar.
The Phaeothamniophyceae is the only class of algae where fucoxanthin and
heteroxanthin occur together.
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A filament and zoospore of Phaeothamnion polychrysis.
Also included is the fine structure of a zoospore.
• Pinguiophyceae include marine planktonic unicellular flagellates as
Phaeophyceae
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Phaeophyceans are known as brown algae, whose color is due to the
presence of large amounts of the xanthophyll fucoxanthin in their
chloroplasts, which conceals the rest of the pigments as well as from the
phaeophycean tannins that might be present.
Phaeophyceans are found almost exclusively in marine habitats and are an
important component of the benthic vegetation in the rocky shores of the
northern and southern hemispheres.
Some brown algae live more than a hundred meters deep due to
fucoxanthin, that allows them to use the blue part of the radiation spectrum.
Some occupy the intertidal zone, as in certain fucoids, and can resist
desiccation for hours or even for days (Pelvetia canaliculata).
Laminariales form extensive subtidal “forests”.
Only five genera live in freshwater, but many are found in brackish waters of
estuaries.
Pelvetia canaliculata
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Some algae classified in the Phaeothamniophyceae.
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in Phaeomonas, or no flagellate as in Pinguiochrysis, with a high content in
omega-3 fatty acids.
These fatty acids are the basis for choosing the latin noun “Pingue”
(meaning fat, grease) as the root of the class name.
The high percentage of unsaturated fatty acids, and the lack of a cell wall,
make these algae desirable as a source of unsaturated fatty acids and of
animal feed.
Algae classified in the Pinguiophyceae
Laminariales
• There are no unicellular or colonial organisms and the algae are basically
filamentous, pseudoparenchymatous, or parenchymatous.
• Many phaeophyceans such as Ectocarpus are branched filaments.
• When branched filaments of one or several axial filaments are joined by
mucilages, they form pseudoparenchymatic thalli called haplostichous, as
in Leathesia.
• The thalli called polystichous are parenchymatic, as in Sphacelaria.
• Polystichous thalli originate by the division of their cells in all directions,
causing a thickening of the thallus and cell differentiation: an outer layer
consisting of pigmented cortical cells and an inner medullar layer of
unpigmented cortical cells.
Ectocarpus
Leathesia
• Some phaeophyceans have air bladders or vesicles in their thalli
which increase their buoyancy, allowing them to live upright and
rooted to the substrate, as in Ascophyllum nodosum, or floating, as
in Sargassum natans.
• Large concentrations of the latter algae gave its name to a region of
the Atlantic Ocean known as the Sargasso Sea.
• Brown algae provide habitat and a food source for many marine
animals.
• Traditionally, they have been used by man as fertilizers for their high
phosphate content.
• Some, like Laminariales, accumulate iodine in a concentration
10,000 times higher than that found in the sea.
Sphacelaria
Ascophyllum nodosum
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As characteristic storage products, they accumulate
the polysaccharide laminarin, an insoluble polymer
composed mainly of β-linked glucans.
The cell wall consists of an inner layer of cellulose
fibers and an outer external layer of mucilage,
comprising colloidal substances called phycocolloids,
such as alginates, which are salts of alginic acid, and
the substance fucoidan (or fucoidin), which is mainly
composed of sulfated polysaccharides.
Both alginates and fucoidan are of commercial interest.
In the phaeophycean Padina, calcium carbonate
deposits (i.e., calcification of the wall) are present in
the form of aragonite.
The cells contain a single nucleus with small
chromosomes and one or more chloroplasts, whose
structure can be laminar, perforated, discoid or
lenticular.
The chloroplasts also have chlorophylls a, c1, and c2.
Plastids have their own membrane and two
membranes from the endoplasmic reticulum.
Sometimes, the outer membrane of the chloroplast
E.R. is continuous with the outer membrane of the
nuclear envelope.
Pyrenoids, when present, accumulate reserve
polysaccharides around them.
Thylakoids are arranged in packs of three, surrounded
by a girdle lamella.
Sargassum natans
• The greater morphological complexity of Phaeophyceae, and of
algae as a whole, is found in the order Laminariales, in which thalli
have three distinct parts: the holdfast, stipe and blade.
• The parenchymatous Phaeophyceae have plasmodesmata or pores
between most of the cells. These pores are bounded by the
plasmalemma, and protoplasm is continuous from one cell to the
next through them.
Diagram of a hypothetical brown algal
cell. (ce) Chloroplast envelope; (cen)
centrioles; (cer) chloroplast endoplasmic
reticulum; (d) dictyosome; (er)
endoplasmic reticulum; (f) DNA fibrils;
(m) mitochondrion; (ne) nuclear
envelope; (nu) nucleolus; (p) pyrenoid;
(ps) pyrenoid sac; (v) vacuole.
Padina
• Asexual reproduction is by means of zoospores, fragmentation or
specialized multicellular structures called propagules, which are able
to produce adult individuals.
• Sexual reproduction occurs by isogamy, anisogamy or oogamy.
• Life cycles are isomorphic haplo-diplontic or heteromorphic with a
dominance of gametophytes or sporophytes (Laminariales).
• Fucales and Durvilleales have a diplontic cycle.
Branches with propagules in different development stages .
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• Generally the motile cells of the
Phaeophyceae (always the
reproductive cells such as
zoospores or gametes, as there
are no motile vegetative cells)
have a long anterior tinsel
flagellum with tripartite hairs and
a shorter posteriorly directed
whiplash flagellum with a swelling
(fs) near the base fits into a
depression of the cell
immediately above the eyespot.
• The eyespot (stigma) (e)
consists of lipid globules
arranged in a single layer
between the outermost band of
the thylakoids and the chloroplast
envelope.
• The eyespot acts as a concave
mirror focusing light onto the
flagellar swelling, which is the
photoreceptor site for phototaxis
in brown-algal flagellate cells.
representation of a male gamete of Ectocarpus
siliculosus showing the distribution of cellular
organelles. (af) Anterior flagellum; (c) chloroplast;
(e) eyespot; (fh) flagellar hairs (present along entire
length, for clarity only shown on part of the flagellum);
(fs) proximal swelling of the posterior flagellum; (g)
Golgi apparatus; (li) lipid body; (m) mitochondrion; (mb)
microbody; (mt) microtubules; (n) nucleus; (p) pyrenoid;
(pf) posterior flagellum; (v1) physode; (v2) storage
granule; (v3) vesicles with cell wall or adhesive
material.
• Two types of sexual reproductive structures (sporangia or
gametangia) can be observed in Phaeophyceae.
– One type has multilocular (plurilocular) structures , in which each
cavity produces a flagellate cell by mitosis. This type can be
produced either in gametophytes or in sporophytes.
– Other reproductive structures are unilocular, formed by a single
cell, in which 16 to 128 flagellate haploid spores are formed by
meiosis. This type is mainly produced in sporophytes.
Brown algae consist of more than 250 genera and about 1,500 species.
Ectocarpus fasciculatus, plurilocular (a) and unilocular (b) sporangia.
Diversity in brown algae. A. Desmarestia dudresnayii. B. Undaria pinnatifi da. C.
Laminaria ochroleuca. D. Sargassum muticum.
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Most phaeophyceans with simple thalli and
isomorphic reproductive cycles belong to the
order Ectocarpales.
Ectocarpus is cosmopolitan; thalli are
uniseriate branched filaments with
heterotrichous organization and diffuse
intercalary growth.
The haploid gametophytes and diploid
sporophytes are morphologically identical.
The gametophytes produce multilocular
(plurilocular) gametangia that generate male
and female gametes, which are
morphologically identical but have a different
behavior.
Male gametes are chemotactically attracted
towards female gametes by the substance,
ectocarpene.
After gamete fusion, the zygote, without a
resting stage, originates a sporophyte, in which
either unilocular sporangia or plurilocular
sporangia are produced. The latter originates
diploid asexual spores that can generate
diploid sporophytes.
Gametes can also produce new gametophytes
by parthenogenesis, and even haploid
zoospores can fertilize to produce sporophytes.
In Ectocarpus, multilocular structures are
formed on both haploid and diploid thalli.
Phlorotannins and physodes
• Phlorotannins (phaeophycean tannins) are stored in physodes (Fig. )
in the cytoplasm of many brown algae. Phlorotannins are formed by
Golgi by polymerization of phloroglucinol (1,3,5-tri-hydroxybenzene)
• The tannins are non-glycosidic (do not contain sugars), bind proteins,
have strong reducing action, and are astringent to the taste. They are
readily oxidized in air, resulting in the formation of a black pigment,
hycophaein, giving dried brown algae their characteristic black color.
• Phlorotannins have been postulated to function in
– (1) deterring grazing by herbivores,
– (2) absorbing ultraviolet radiation, and
– (3) serving as a component of cell walls
gametophytes
Chemical structure of phloroglucinal, the basic building
Transmission electron micrograph showing physodes block of polyphenols and the chemical structure of the
polyphenol procyanidin.
around the nucleus.
The life cycle of Ectocarpus siliculosis.
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• Desmarestiales contains
a single family with two genera,
Desmarestia and
Himantothallus, both with
pseudoparenchymatous thalli
and heteromorphic life cycles,
microscopic gametophytes and
oogamous sexual reproduction.
• This order is distributed
worldwide in temperate and cold
waters.
• Phlorotannins are not normally secreted outside the cell. It is necessary
for the cells to be damaged before the phlorotannins are released.
sporophytes
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sporophytes
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gametophytes
The order Cutleriales is
characterized by biflagellate gametes.
The male gamete is much smaller than
the female one, which produces the
hormone multifidene that attracts male
gametes.
The order includes species with life
cycles with heteromorphic alternation of
generations, as in Cutleria, in which the
gametophyte is predominantly
composed of dichotomously branched
flat thalli that produce micro and
megagametangia grouped in sori.
The sporophyte is flat and crustose and
was described as a different genus
named Aglaozonia.
In Zanadinia, the life cycle shows
isomorphic alternation of generations.
sporophytes
gametophytes
Desmarestia
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The life cycle of Desmarestia. (
The life cycle of Cutleria multifida.
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• Sphacelariales consists
Dictyotales
In the order
, thalli are flat,
dichotomous or fan-shaped, growing by one or more
apical cells.
Sporangia and gamentangia are grouped in sori.
Sporangia (unilocular) produce four or eight immobile
haploid meiotic spores.
Sexual reproduction occurs by oogamy.
The life cycle of Dictyota involves the isomorphic
alternation of generations.
Gametophytes are dioecious, and the oogonia are
arranged in sori, each oogonium produces a single
immobile cell (egg) which liberated through the wall
In multilocular gametangia, male thalli develop
pyriform sperm with two laterally inserted flagella.
Only the pleuronematic (tinsel) flagellum is externally
visible, since the other flagellum is reduced to the
basal body.
of several genera distributed
from temperate to tropical
waters.
The thallus is a small tuft of
branches with a parenchymatous
construction in which growth is
by a prominent apical and
pigmented cell.
For asexual reproduction, the
thallus develops specialized
branches called propagules.
Fertilization can be oogamous,
as in Cladostephus and
Halopteris, or isogamous as in
Sphacelaria.
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gametophytes
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sporophytes
sporophytes
gametophytes
The life cycle of Dictyota dichotoma.
Left figure: Diagrams of reproductive structures of
Dictyota in cross section of the thallus. (a) Sorus with
antheridia. (b) Sorus with oogonia. (c) Tetrasporangium
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The order Laminariales is characterized by a life cycle
involving the heteromorphic alternation of generations, between
large sporophyte and microscopic gametophyte.
Sexual reproduction by oogamy and plastids without pyrenoids.
Sporophytes reach several meters in height and have a marked
morphological differentiation.
They are attached to the substrate by a system of rhizoids,
called haptera, from which a cylindrical stipe rises, ending in a
widening laciniate blade consisting of several layers of cells.
Growth in length is due to an intercalary meristem located
between the end of the stipe and the blade.
Laminaria hyperborea can live for several years and each year
it renews its blade. In winter a new meristem inserted in the
base of the blade generates a new blade, and the old one is
destroyed at the apex.
The thalli increase in thickness by a layer of cells with
meristematic activity known as meristoderm (MR).
The life cycle of Sphacelaria
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Fertilization takes place during spring tides in the warmer months, when eggs
and sperm are discharged.
The egg secretes the pheromone dictyotene
Many species of this order, such as Dictyota dichotoma or fan-shaped Padina
pavonia, are common in temperate and warm coasts.
Species of Dictyota produce terpenoids, such as pachydictyol and (6R)-6hydroxydichotoma-3, 14-diene-1,17,dial, that inhibit grazing of Dictyota by
herbivorous fish, amphipods, and sea urchins
Dictyota dichotoma Thallus with regular dichotomous branching
Padina pavonia
Cross section of the blade of Laminaria.
CX: cortex.
ME: medulla.
MR: meristoderm
Nereocystis luetkeana
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Gametophytes in Laminaria, as in
all Laminariales, are microscopic.
Female gametophytes consist of
few cells. Oogonia produce a
single egg, which when mature
leaves the oogonium through a
pore, but remains attached to the
oogonium wall.
Male gametophytes are branched
filaments. Male unicellular
gametangia produce a single
biflagellate gamete.
After fertilization, the diploid
sporophytes grow on the female
gametophyte.
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sporophytes
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The stipe of Laminaria is cylindrical. In cross section, it shows a meristoderm
that produces small pigmented cells outwards and cortical unpigmented cells
inwards.
Cortical cells increase in size from the outside inwards.
Mucilaginous ducts (canals) are located in the outer cortical layers. These
ducts are formed by a ring of secretory cells.
Inside the stipe, a medulla is formed by elongated cells with a narrow lumen,
known as hyphae or trumpet cells (TC), arranged in a network.
Trumpet cells are widened at their ends and consist of sieve plates, through
which there is a transport of substances similar to vascular plants.
Some species of Laminaria can live for several years and produce a growth
ring per year in their old stipes.
gametophytes
Trumpet Hyphae
The life cycle of Laminaria japonica
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The order Fucales comprises
phaeophyceans in which the life
cycle is diplontic, and thalli are
thought to grow by an apical cell that
generates a promeristem.
In these algae, adult plants are
diploid so that meiosis is gametic.
In Fucus, the thalli are dichotomous,
ribbon-shaped, with a central
thickening or midrib, fixed to the
substrate by means of a disc.
The reproductive organs are
arranged at the apex of the thallus,
in widened parts known as
receptacles, constituted by multiple
cavities or conceptacles sunk in the
thallus.
Inside the conceptacles, male
gametes are found in the antheridia
and eggs in oogonia, together with
sterile filaments or paraphyses that
project outside the conceptacle
through an ostiole.
• Laminariales are subtidal algae which form large populations in
temperate and cold seas, comprising the biggest algae such as
Macrocystis pyrifera which can reach 50 meters in length.
• Species of Laminaria (L. hyperborea, L. digitata, L. ochroleuca) and
Saccharina are common in Atlantic coasts.
• In Pacific coasts, other genera, such as Macrocystis, Nereocystis
and Eisenia are dominant.
• Laminariales, collected in nature or cultivated, are the main source
of alginates and other compounds such as mannitol and iodine.
Macrocystis pyrifera
Laminaria
Macrocystis
Nereocystis
The life cycle of Fucus sp. (F. vesiculosus and F. serratus).
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• Species of the genus Fucus (F. vesiculosus, F. spiralis, F. serratus)
are common in cold and temperate coasts of the northern
hemisphere, while other fucoids, as numerous Sargassum species
live in tropical waters worldwide.
• Cystoseira is a genus that may have originated in the Mediterranean
and is characteristic of well structured coastal communities.
• Caulocystis and Horrmosira are common in the waters of the South
Pacific.
Cystoseira
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Kombu is the Japanese name for the dried macroalgae that is derived from
a mixture of Laminaria species and used as food. These include L.
longissima, L. japonica, L. angustata, L. coriacea and L. ochotensis.
These are all harvested from natural sources.
The first three of the above are the main components of the harvest.
The plants grow on rocks and reefs in the sublittoral zone, from 2 to 15 m
deep. They prefer calm water at temperatures between 3 and 20 C. The
naturally growing plants are biennial and are ready for harvesting after 20
months. Harvesting is from June to October.
As demand grew in the 1960s,
attempts were made to develop
artificial cultivation methods, but
the 2 yr cycle meant the costs
were too high.
In the 1970s, forced cultivation
was introduced, reducing the
cultivation period to 1 yr, similar to
the system developed in China in
the early 1950s.
Today, about one third of Japan’s
requirements come from
cultivation, with the remaining two
thirds still coming from natural
resources.
For cultivation, Laminaria must go
through its life cycle
(d) Long line with Laminaria after 8 months of growth (Yellow Sea, China).
(e) Long line showing attached Laminaria plants (South Korea).
(f ) Young sporophytes growing on long line
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Antheridia are on branched filaments, producing 64 biflagellate sperms after
meiosis.
Antheridia have two walls. The breakage of the outer wall releases the
sperm in a package, and then the second wall breaks and the sperm swim
attracted by the sexual pheromone, fucoserratene, produced by the egg.
The oogonia have three walls that surround eight eggs. Breakage of the
outer envelope releases the entire assembly, and after the disruption of the
remaining walls, the eggs float until they are fertilized.
The zygote produces a cellulose wall, and then it attaches to the substrate
and begins to divide to give a new sporophyte.
Life cycle of a monoecious species of Fucus
• Phaeophyceae are thought to have evolved from
ancestors that had reproductive life cycles with the
isomorphic alternation of generations, fertilization by
anisogamy or isogamy and simple morphological types,
like Ectocarpus.
• They evolved towards forms with a progressive reduction
of the gametophyte and increased morphological
complexity of the sporophyte, as in Laminaria.
• Diplontic life cycles and fertilization by oogamia, as in
Fucus, are considered the most advanced characters
after an extreme reduction of the haploid generation.
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Another exploited kelp the Undaria sp., known as wakame, which together with
Laminaria sp. is one of the two most economically important edible algae.
U. pinnatifida is the main species cultivated; it grows on rocky shores and bays in the
sublittoral zone, down to about 7 m, in the temperate zones of Japan, the Republic of
Korea, and China
Undaria is an annual plant with a life cycle similar to Laminaria.
It has an alternation of generations with the large macroalga as the sporophyte and a
microscopic gametophyte as the alternate generation.
Undaria is processed into a variety of food products.
The crude protein content of wakame and kombu is 16.3 and 6.2 g (g/100 g),
respectively, and both algae contain all essential amino acids, which account for
47.1% of the total amino acid content in wakame and for 50.7% in kombu.
Brown Algae Ecological Significance
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Laminaria species contain about 10% protein, 2% fat, and useful amounts
of minerals and vitamins, though generally lower than those found in nori.
For example, it has one tenth the amounts of vitamins but three times the
amount of iron compared with nori.
Brown macroalgae also contain iodine, which is lacking in nori and other red
macroalgae.
In China, haidai is regarded as a health vegetable because of its mineral
and vitamin content, especially in the north, where green vegetables are
scarce in winter.
It is usually cooked in soups with other ingredients.
In Japan, it is used in everyday food, such as a seasoned and cooked
kombu that is served with herring or sliced salmon.
• Hizikia fusiforme is another brown algae popular as food in Japan
and the Republic of Korea known as Hiziki.
• It is collected from the wild in Japan and cultivated in the Republic of
Korea.
• The protein, fat, carbohydrate, and vitamin contents are similar to
those found in kombu, although most of the vitamins are destroyed
in the processing of the raw macroalgae.
• The iron, copper, and manganese contents are relatively high,
certainly higher than in kombu. Like most brown macroalgae, its fat
content is low (1.5%) but 20–25% of the fatty acid is
eicosapentaenoic acid (EPA).
• Japan produces also Cladosiphon okamuranus. The harvested
macroalgae are washed, salted with 20–25% salt, and let to
dehydrate for about 15 days. Drained fronds are sold in wet, salted
form in packages.
Productivity: Up to 1 kg C / m2 / y (Graham et al. 2008)
Brown Algae Viewing Sites
Point Lobos State Preserve, CA
(just south of Monterrey CA)
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Brown Algae Ecological Significance
Brown Algae Economic Significance
Brown Algae Viewing Sites
Brown Algae Economic Significance
Alginate
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