Phaeophyta
Phaeophyta are greenish-brown colored algae that contain fucoxanthin, beta-
carotene and chlorophyll a and c. They are the most complex forms of algae,
commonly adapted in the marine environment.
Habitat
The brown algae are widespread and with few
exceptions all are marine. They grow attached
to the rocks, shells, or coarser algae such as
the kelps. In general, the brown algae flourish
in colder ocean waters and on rocky coasts,
where they grow attached in intertidal or
littoral zone e.g. the member of fucaceae and
Laminariales.
Length
The length of Phaeophyta can range from a
microscopic length to several meters. The
longest size measured is about 30 meters.
Plant Body
The filamentous form are uniaxial, however in
parenchymatous form the plant body may be
differentiated into a holdfast, through which it
is attached to the substratum; a long or short
stipe; and expanded leaf like fonds that act as
photosynthetic and reproductive organ.
Growth
The growth of the thallus in primitive brown
algae is by intercalary meristems at the base of
the hair or filament. This type of growth is
called trichothallic growth, e.g., in ectocarpus.
Cell wall
Phaeophyta are the most complex forms of algae. The cell walls are composed of
cellulose and alginic acid. The cell wall is composed of two layers
Inner cellulose layer
Outer pectin layer
Reproduction
Like other evolved algal species, reproduction of this algae takes place by both
sexual and asexual means.
Asexual reproduction by pyriform or spindle shaped motile zoospores with
two unequal flagella
Sexual reproduction ranges from isogamy to oogamy through anisogamy.
Alternation of generation
Higher Phaeophyta have life cycle consisting of both haploid and diploid stages,
referred to as an alternation of generation. The thallus representing haploid stage
and diploid stage may be similar (isomorphic) or different (heteromorphic).
Reserved food
Unlike green algae or Chlorophyta, they lack true starch.
The food reserves contain sugar, higher alcohol and other complex forms of
polysaccharides.
Kelps
The members of Phaeophyta belonging to Laminariales are called kelps.
Kelps are the only algae with a significant internal tissue difference. kelps act as
some sort of conductive tissues because xylem and phloem are absent in them.
Phaeophyta Uses
► Commercially exploited Phaeophyta include those belong to the orders,
Laminariales and Fucale’s.
► Previously, marine seaweeds of Phaeophyta were used for the extraction of
iodine and potash.
► In recent times, Phaeophyta are extensively exploited for the extraction
of alginic acid, which is used for deriving alginate, a major colloidal gel used as a
stabilizer, emulsifier or binder in many industrial applications.
► Apart from alginic acid, agar, carrageenan are also derived from Phaeophyta.
► Commercially, alginate is used in fabric printing, baking, toothpastes, soaps, ice
creams, meat preservation, etc.
► Another use of Phaeophyta is in the manufacturing of agricultural or
horticultural sprays.
► In addition, Phaeophyta is used as a food source. The brown algae, laminaria is
cultivated on man-made algal ponds (using ropes) to produce food supplements
and alginates.
► Harvested Phaeophyta are then processed to prepare seaweed meals. These
highly proteinaceous seaweed meals are exported to various countries, especially
to solve the problem of malnutrition.
Brown algae have proven to be one of the most adaptable species and are also one
of the major contributing factors in the maintenance of a balanced ecosystem.
Ectocarpus
Ectocarpus is a genus of filamentous brown alga that is a model organism for
the genomics of multicellularity. Among possible model organisms in the brown
algae, Ectocarpus was selected for the relatively small size of its mature thallus
and the speed with which it completes its life cycle.
Taxonomic Position
Division: Phaeophyta
Class: Isogeneratae
Order: Ectocarpales
Family: Ectocarpaceae
Genus: Ectocarpus
Occurrence of Ectocarpus:
Different species of the genus Ectocarpus (Cr. ekos — external and kapos — fruit)
is found throughout the world. They grow in marine habitat, either free-floating,
epiphytes (on other sea plants) or lithophytes (on rocks). They are commonly
available in both tropical and temperate sea.
Plant Body
The Plant body consists of sparsely or
profusely branched uniseriate filaments and
exhibits heterotrichous habit. There are two
types of filaments;
Prostrate filament
Erect filament
Prostate Filament: The prostrate system is
comprising of creeping, septate, profusely
branched filament that are attached to the
substratum with the help of rhizoids. In
epiphytic species this system occasionally
penetrates the host. In free floating species
the prostate system is poorly developed. The
prostrate system is profusely branched and
attached with the substratum.
Erect Filament: The erect system develops
from the prostrate system which remains free-
floating. It is much branched and well-
developed. Both the main axis and branches
are uniseriate, but the lower part may become
multiseriate. The branches terminate into an
acute point forming a hair.
Two types of plant bodies are differentiated genetically, one is haploid and other
one is diploid. Both haploid and diploid plants are morphologically identical.
Cell Structure of Ectocarpus:
The cells are rectangular or cylindrical. Cell wall is differentiated into outer pectic
and inner cellulosic layers. The characteristic gelatinous substance present in the
cell wall is composed of algin and fucoidan. Inner to the wall, cell membrane is
present which encircles the protoplast.
The protoplast contains one central nucleus
and many chromatophores. The number and
shape of chromatophore varies with species.
They may be ribbon-shaped, band-shaped,
discoid etc. and are associated with
pyrenoids.
The photosynthetic pigments are chlorophyll
a, chlorophyll c, β-carotene and fucoxanthin.
The fucoxanthin masks the chlorophyll and
gives the characteristic brown colouration.
The cytoplasm contains many vacuoles,
which are called phycids. The phycids
contain polyphenols, probably function as
lysosomes. Morphologically, haploid, and
diploid vegetative filaments are almost alike,
but the cells of haploid filaments are
comparatively shorter in length than the
diploid filaments.
Growth:
The nature of growth varies with the region of plant body and with species. The
erect system shows intercalary, diffuse or trichothallic growth, whereas it is apical
in prostrate system.
Reproduction
Ectocarpus reproduce asexually by zoospores and sexually by isogamy or
anisogamy. The oogamous type of sexual reproduction is absent.
Sexual Reproduction:
The sexual reproduction is both isogamous and anisogamous type. Oogamy is
absent. Anisogamy is very common. Anisogamy may be of two types:
morphological anisogamy (E. secundus) and physiological anisogamy (E.
siliculose). The gametes are produced inside the plurilocular gametangia,
developed on haploid plants.
Plurilocular Gametangia:
They are large, elongated, sessile or short stalked, multicellular structures.
Morphologically, both plurilocular gametangia and plurilocular sporangia are
alike. The plurilocular gametangia produce haploid gametes; on the other hand,
plurilocular sporangia produce diploid zoospores.
Though both are morphologically more or less alike, the gametes are slightly
smaller in size than the zoospores. The development of plurilocular gametangia is
alike with the development of plurilocular sporangia. The gametes are liberated
from the gametangia following the same procedure as that of zoospore liberation
from the plurilocular sporangia
Fertilisation:
Fertilization results in a diploid zygote. The zygote germinates into a diploid
sporophyte without undergoing any resting period.
Alternation of Generation:
Ectocarpus show isomorphic alternation of generation. the sporophyte is diploid
and bears two types of sporangia in which zoospores are formed because of
mitosis, and the unilocular sporangia in which the zoospores are produced
meiotically. The mitozoospores germinates into a diploid sporophyte whereas the
Mei zoospores germinate to give rise a haploid gametophyte plant that bear
plurilocular gametangia. These gametophytes are produced in the gametangia
which on fusion results into a diploid zygote that germinates into a diploid
sporophytes plant.
