Chara Structure and Reproduction Notes By // Rohit Jirobe //
Chara
It grows in pools, ponds and lakes.
It is commonly known as stone wort or brittle wort because the plant body is encrusted with calcium carbonate. This alga grows in clear still waters and does not grow in contami-nated waters.
Chara is world-wide in distribution. It includes about 90 species. Of these 27 species are found in India.
The common Indian species are:
Chara vulgaris , Chara zeylanica , Chara corallina , Chara nuda , Chara erythrogyna , Chara fragitis.
Thallus Structure
Chara is a green alga. It is commonly called stone wort or brittle wort because the thallus is encrusted with lime.It is a freshwater form.
It is a submerged attached alga.
The thallus of Chara is macroscopic. It is erect and grows to a height of 20-30 cms.
The plant body is called thallus.
The thallus consists of a main axis and rhizoids.
The plant is a haploid gametophyte.
The plant is attached to the substratum by means of rhizoids.
The rhizoids are uniseriate and branched.The main axis consists of nodes and internodes.
The node is made up of two central cells surrounded by 6 to 20 peripheral cells called cortical cells.
The internode is made up of a single long central cell called axial cell surrounded by many cortical cells.
The node bears three types of branches namely 'leaves', stipulodes and axillary branches.
The 'leaves' arise as a whorl around the node. They have limited growth. They are also called primary laterals or branchlets.
The 'leaves' also contain nodes and internodes.
The nodes of leaves contain a whorl of branches called stipulodes.
In addition, the nodes of 'leaves' contain sex organs such as nucule (oogonium) and glob-ale (antheridium).
The stipulodes are present as a whorl around the node.
The node of the main axis bears a third branch. It grows up from the axil of the 'leaves" Hence it is called axillary branch. As it grows laterally from the main axis, it is also called lateral branch.
The axillary branches also contain nodes, internodes, 'leaves', stipulodes and sex or-
gans similar to that of main axis.
The leaves of the axillary branches are called secondary laterals.
The cells that surround the internodal cell constitute cortex.
The process of development of cortex is called cortication.
The cortex of each internode is contributed by the adjacent two nodes.
One set of cortical cells grow downwards from the upper node and the other set of cortical cells grow upwards from the lower node. These two sets of cells elongate and meet in the middle of the internode ensheathing the central internodal cell. This sheath of cortical cells constitutes the cortex.
The cortex is present in most of the species of Chara.
The species of Chara containing cortex is called corticated species. Eg. C. zeylanica. The species that do not contain cortex is called ecorticated species. Eg. C. nuda.
Cell Structure
The nodal cells are small and the internodal cells are large.
The cell has a thick cell wall.
The cell wall is differentiated into an inner layer consisting of cellulose and an outer layer consisting of pectin and calcium carbonate crystals.
Inner to the cell wall is a plasma membrane around the protoplasm.
The protoplasm contains a haploid nucleus and a few discoid chloroplasts.
The pyrenoid is absent.
The chloroplast contains chlorophyll-a and-b, carotenes-a, -B, and -y,lutein, lyco-pene, violaxanthin and neoxanthin.
Starch granules are the reserve food.
Growth
Reproduction
Chara reproduces by two methods. They are:
Vegetative reproduction
Sexual reproduction.
Vegetative Reproduction
Vegetative reproduction takes place by the following methods:1. Amylum stars 2. Bulbils 3. Tubers 4. Secondary protonema.
1. Amylum Stars
These are star-shaped, multicellular bodies.They are produced on the lower nodes of the main axis. Each amylum star is an aggregation of cells rich in starch.
These stars get separated from the nodes and grow into new plants. Eg.Chara stelligera.
2. Bulbils
Bulbils are small, rounded, tuber-like structures produced from the lower nodes and rhizoids of Chara. When the bulbils are detached from the nodes, they grow into new plants. Eg Chara aspera.3. Tubers
Tubers are ovoid bodies rich in starch,They are produced on the rhizoids.
They are also known as root bulbils.
During favourable season, they get separated and grow into new plants.
4. Secondary Protonema
The filamentous structures arising from nodes or rhizoids of old stem of Chara are calledThe secondary protonema forms nodes and internodes.
When the protonema gets detached from the axis, it develops into a new plant.
Sexual Reproduction
The sexual reproduction in Chara is oogamous type as the eggs are non-motile.Chara is a haploid gametophyte.
The sex organs are multicellular.
They are protected by a sterile envelope.
The male sex organ is called globule or antheridium.
The female sex organ is called nucule or oogonium.
The sex organs are produced at the nodes of the 'leaves'.
Globule
It develops at the nodes of 'leaves'. It is formed on the lower side.
The mature globule is a large, hollow, spherical structure. It is yellow or red in colour.
It has a short stalk called pedicel cell which projects into the cavity.
The wall of the globule consists of 8 curved plate-like cells called shield cells.
The outer surface of the shield cell is convex and the inner surface is concave.
From the centre of each shield cell arises an elongated cell called manubrium. Thus the globule contains & manubria in the hollow space.
At the tip of each manubrium, there is one or two rounded cells called primary capitulum ot primary head cell.
cells. Each primary capitulum produces 2-6 secondary capitulum cells or secondary head
Each secondary capitulum produces two long uniseriate filaments called antheridial fila-ments of spermatogenous filaments. Each spermatogenous filament consists of 50-200 sperm mother cells.
Each sperm mother cell gives rise to an elongated spirally coiled, biflagellate sperm or spermatozoid.
The spermatozoid of Chara is spirally coiled with about three turns.
The anterior end is thin and pointed.
A vesicle is present at the posterior end of the body.
Two flagella are attached at the anterior end.
Each spermatozoid has an elongated coiled nucleus and has a cytoplasmic sheath all over its body. The spermatozoids are liberated as the shield cells separate.
Nucule
Nucule is the female sex organ of Chara. It is also known as oogonium.
It is produced at the nodes of 'leaves'. It is located on the upper side.
The nucule is oval in shape and has a short pedicel.
The mature nucule is black in colour.
It contains a single egg.
The egg cell contains a single basal nucleus, dense cytoplasm and reserve foods like
starch and oils.
The egg is surrounded by a sterile protective envelope.
The protective envelope consists of five spirally elongated sterile cells called tube-cells.
Each tube cell cuts off a small crown cell at the apex of the nucule.
These five crown cells together form a corona at the apex of the nucule.
The egg contains a colourless area at the apex called receptive spot.
Fertilization
In mature nucule, the tube cells around the oogonium separate from one another. Hence narrow slits are formed in the envelope.The oogonial wall at the receptive spot gets gelatinized.
The spermatozoids enter the nucule through the slits of the envelope.
One of the spermatozoids enters the egg cell through the gelatinized oogonial wall and fertilizes the egg
Germination of Oospore
Conclusion
The life cycle of Chara is haplontic type as the haploid phase is dominant. The vegetative thallus is a haploid gametophyte (N). It produces eggs and spermatozoids by simple mitosis. The spermatozoid fuses with the egg to form a diploid zygote (2N). The zygote undergoes meiosis to form haploid filamentous primary protonema. The primary protonema grows into a new gametophytic plant (N). Here the diploid stage is represented only by the zygote. There is no alternation of generation.
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