Life Cycle Of Sargassum
Classification
Sub- division Algae
Class- Phaeophyceae
Order- Fucales
Family- Sargassaceae
Genus- Sargassum
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| Sargassum Thallus |
Thallus
Study the external structure of thallus.
1. Thallus is erect, thalloid and branched.
2. It remains attached to the substratum by a discoid holdfast.
3. Main axis stands out from the holdfast. The height varies from a few centimeters to many centimeters.
4. Main axis bears large number of primary laterals forming a larger part of vegetative structure. Branches are radially symmetrical and spirally arranged.
5. Secondary branches are repeatedly branched.
6. Many branches are flattened along the plane of branching into leaf-like structures called 'leaves'.
7. Leaves are narrow and their margins are mostly serrate. A few species also show a clear mid-rib.
8. In the lower parts, leaves are replaced by air bladders. However, leaf or its part is modified almost at any place into an air bladder.
9. Leaves show minute pores on both of the surfaces which are ostioles (or openings) of conceptacles (sterile) or cryptostomata or cryptoblasts.
10. In the axils of foliaceous branches (leaves) is situated a series of repeatedly branched receptacles which bear reproductive structures.
Axis
Place a small piece of axis in the pith after removing the leaves.
Cut a T.s., stain in safranin and mount in glycerine to study the internal structure.
1. The section is almost circular in outline.
2. It is differentiated into three regions:
(i) meristoderm,
(ii) cortex and
(iii) medulla.
3. Meristoderm is the outermost single celled layer. It consists of many, small and compactly placed cells covered by mucilage. Cells are rich in chromatophores and reserve food material. The cells remain meristematic thus the layer is termed as meristoderm.
4. Cells of the meristoderm are photosynthetically active and, therefore, constitute assimilatory region.
5. Cortex forms most part of the axis. Cells aren narrow and elongated with many intercellular spaces. Cells possess large amount of reserve food material. This region is also known as storage region.
6. Medulla occupies the central part of the axis. It consists of narrow, elongated and double-walled cells, inner wall being thin than the outer.
7. The function of medulla is to transport water and essential nutrients. Hence, it is a also called as conducting region.
Leaf
Place a leaf in the pith, cut a T.s., stain in safranin and mount in glycerine to study the internal structure.
1. T.s. of leaf shows 3 regions similar to those found in axis. These are-meristoderm, cortex and medulla.
2. Meristoderm forms the outermost layer of the leaf. Cells are small, compactly arranged and rich in chromatophores and reserve food.
3. Cortex constitutes major part of the tissues. Cells are thin and contain large amount of reserve food material.
4. Medulla occurs only in central region of the leaf indicating mid-rib. It is absent from the wings.
5. In the leaf are found many sterile conceptacles distributed on both of its surfaces (also known as cryptostomata or cryptoblasts).
6. Each cryptoblast opens to the exterior by an opening-ostiole (visible externally as black dots or pores).
7. Below an ostiole is situated a flask-shaped cavity-conceptacle. The wall of this cavity is lined by cells.
8. The floor of the wall bears many multicellular and unbranched hair called paraphyses. These protrude outside through an ostiole.
9. Thickness of the leaf is maximum in the mid-rib region and decreases toward the wings.
Air bladder
Place a leaf in the pith, cut a T.s. through swollen air bladder stain the section in safranin, mount in glycerine and study the internal structure.
1. Air bladder appears circular in outline.
2. It is enveloped by a distinct mucilage.
3. T.s. shows outermost meristoderm, followed by cortex and the central air cavity.
4. Meristoderm is made of radially clongatedt thin walled cells. It is followed by a large and thin-celled cortex.
5. In the centre is a large air cavity filled with gases.
6. Air bladders help in gaseous exchange and buoyancy.
Male conceptacle
Study a slide showing T.s. of male conceptacle.
1. Plants may be monoecious or dioecious.
2. Antheridia are found in male conceptacles.
3. Conceptacles occur only is specialized branch system called receptacle or receptacular branch.
4. Male conceptacles are smooth externally.
5. Many conceptacles are found in a male receptacular branch.
6. Conceptacle is a flask-shaped cavity opening by a pore called ostiole.
7. Wall of the conceptacle is made of small and flat cells rich in chromatophores.
8. Numerous multicellular hairs arising from near the ostiole project outside. These are called periphyses.
9. Other types of multicellular hairs arising from the floor of the cavity are called paraphyses.
10. Some of paraphyses are branched and hold one or more antheridia at the tips of the branches.
11. Each antheridium has a thick wall made of two layers.
12. On maturity about 64 biflagellate antherozoids are produced.
Female conceptacle
Study a slide showing T.s. of female conceptacle.
1. The plants may be monoecious or dioecious
2. Oogonia are found in female conceptacles.
3. Conceptacles occur only in specialised branch system called receptacle or receptacular branch.
4. The female receptacular branch is spinous.
5. Female receptacular branch has many female conceptacles.
6. Conceptacle is a flask-shaped cavity opening by a pore called ostiole.
7. Numerous multicellular, unbranched hairs arising from near the ostiole and projecting outside are called periphyses.
8. The wall of the conceptacle is lined by small and flat cells, rich in chromatophores.
9. A few multicellular, unbranched hairs also arise from the floor of the cavity and are called paraphyses.
10. Numerous oogonia arise directly from the wall of the conceptacle.
11. Oogonium is sessile or shortly stalked (most of the stalk cell being embedded in the wall).
12. Each oogonium is oval to sub-spherical with a three layered wall.
13. At maturity oogonium has a single, large and uninucleate egg.
Reproduction in Sargassum
Vegetative Reproduction:
Fragmentation:
Sargassum can reproduce vegetatively through fragmentation. Pieces of the
thallus (the main body of the algae) can break off due to physical forces such
as wave action or human activities. These fragments can then drift with ocean
currents and settle in new areas where they can grow into new individuals.
Apical
Growth: Sargassum has apical growth regions where new growth occurs. These
regions are located at the tips of branches. As the algae grows, these tips
continuously elongate, producing new segments and branches, thus allowing for
vegetative propagation.
Sexual Reproduction:
Gametogenesis:
Sargassum exhibits a complex life cycle with alternation of generations. The
diploid (2n) sporophyte phase produces specialized structures called
conceptacles, which contain reproductive structures known as conceptacular
receptacles.
Gamete
Release: Within the conceptacular receptacles, male and female gametangia
develop. Male gametangia, or antheridia, produce sperm cells, while female
gametangia, or oogonia, produce eggs. These gametes are released into the
water.
Fertilization:
External fertilization occurs when sperm released from antheridia fertilizes
eggs released from oogonia in the surrounding water. This results in the
formation of a zygote.
Zygote
Development: The zygote develops into a diploid (2n) sporophyte, which grows into
a mature Sargassum plant, completing the life cycle.
The alternation of generations in Sargassum involves a diploid sporophyte generation and a haploid (n) gametophyte generation. The sporophyte produces spores through meiosis, which develop into haploid gametophytes. The gametophytes produce gametes through mitosis, which then fuse during fertilization to form a diploid zygote, restarting the sporophyte generation.
Identification
Sub-division-Algae. (1) Simple thallus, (2) Chlorophyll present, (3) Cell wall of cellulose. Class-Phaeophyceae. (1) Chromatophores yellowish-brown,
(2) Photosynthetic reserves-laminarin and mannitol,
(3) Motile reproductive cells-pyriform and flagellated,
(4) Flagella laterally inserted and unequal.
Order-Fucales.
(1) Plants parenchymatous, morphologicallya and anatomically differentiated,
(2) Medulla filamentous,
(3) Asexual reproduction absent,
(4) Sex organs in conceptacles.
Family-Sargassaceae.
(1) Axes terete, bearing distinct foliar organs
(2) Vesicles usually present, lateral or immersed in the terminal branchlets,
(3) Branching of the thallus radial to the central axis.
Genus Sargassum.
(1) Foliar organs narrow, branched, leaf-like with a distinct mid-rib
(2) Vesicles generally lateral
(3) Fertile branches (receptacles) lateral, or terminal panicles.
Hints for collection
It is marine in habitat and remains restricted to tropical seas, mainly of southern hemisphere. In India, species of this genus are found along the east coast, west coast, and Andman and Nicobar islands.
- Sargassum life cycle
- Sargassum reproduction
- Sargassum alternation of generations
- Sargassum vegetative reproduction
- Sargassum sexual reproduction
- Sargassum sporophyte
- Sargassum gametophyte
- Sargassum conceptacles
- Sargassum antheridia
- Sargassum oogonia