Q.17. Describe the structure and reproduction of Chara. (1993, 95)
Related Question-
Q. Describe the various modes of reproduction in Chara. (2008)
Q. Draw the labelled diagram of L.S. of sex organs of Chara. (2003, 10, 11, 12)
Q. Why is Chara known as stonewort ? (2012)
Ans. Sysematic Position: -
Division - Algae
Class - Chlorophyceae
Order - Charales
family - Characeae
Genus - Chara
Occurrence: - Chara is aquatic submerged fresh water, muddy or sandy algae. It usually found in ponds, puddles tanks lakes or slow flowing streams. Many species of Chara occurs over water running lime stone rocks. Species like C. fraglis occurs in such hot springs. Several species of Chara get encrusted with calcium carbonate and become hard, brittle and rough, hence commonly called “stonewort”
Thallus structure: - Plant body is well developed macroscopic and well branched. The height of plant body generally 20-30 cm, it may be 90 cm to 1 meter. The plant body differentiated into many rhizoids and main axis.
(i) Rhizoids: - Rhizoids are branched multicellular thread like structure. These helps attached top land to mud or sand. Oblique septa are present in rhizoids. There are lacking of Node and Internode.
(ii) Main axis: - The main axis is erect and well branched. It is differentiated into nodes and internodes.
(i) Internode: - Internode is long cylindrical undivided single cell. It is much in length than breath. It makes much part of main axis.
(ii) Node: - Node arranged in a definite pattern and is complex man of cells. It consist of a central pair of cells surrounded by 6-20 peripheral cells. From the node of main axis develops 4 types of appendages. i.e., primary laterals, branches of unlimited growth, stipulodes and cortex.
(a) Primary laterals: - These are short branches and arranged in the form of whole on the node or branch of unlimited growth.
These are limited in size and known as branch of limited growth branchlets.
It contains various number of peropheral cells. from these cells develop the stipulodes, but in corticate species these cells give rise to cortex of the axis.
(b) Branches of unlimited growth: - From the node of main axis and from the axil of branch of limited growth, arise one or few branches of unlimited growth. They are often called as axillary branches. These branches possesses nodes and internodes and have primary laterals on their nodes. The axillary branch originate from the primary internodal cell.
(c) stipulodes: - From the basal node of each branchlets develop unicellular, spine-like outgrowths called stipulodes. Two stipulodes develop at the base of each branchlets in the most of the species.
(d) Cortex: - In most species of Chara the long internodal cells of the axis covered by a sheath called cortex. The cortex consists of vertically extending row to cells.
(iii) Cell structure: - The nodal cells have dense and granular cytoplasm, having many discoid chloroplast with lacking of pyrenoids single nucleus centrally located and bounded by a cellulose cell wall.
The internodal cells are very large and surrounded by a cellulose cell wall. A large central vaccide surrounded by parictal cytoplasm with many discoid chloroplast. The outer region is exoplasm and inner endoplasm region more cytoplasmic fluid is present in the endoplasm region. This flluid makes streaming movement with in the cells.
Reproduction: - Only two kinds of reproduction vegetatively and sexually. asexually spores are absent.
Vegetative reproduction: - It reproduces vegetatively by following methods -
(i) Amylum stars: - In some species of Chara some amylum star is an aggregration of cells, looking like a star. The cells are filled with amylum starch. Amylum star, after being detached from the parent plant, grows into a new plant.
(ii) Bulbils: - These are small rounded tuber-like structure which are developed on the rhizoids, e.g. C. aspera. After being detached from the parent plant, they give rise to a new plant.
(iii) Tuber-like bodies: - In certain cases, tube-like bodies arise either from rhizoids or form main axis buried in the soil. Tubers store abundant starch and germinate by producing basal cell and by more transverse divisions.
(iv) Protonemal outgrowths: -Protonemal branches may develop from existing nodes of old plants, primary rhizoid ring or dormant apices. These develop into new plants in a way similar to primary protonema.
Sexual reproduction: - sexual reproduction is advanced type in chara and it is Oogomous type. Sex organs are well developed. The male reproductive bodies are called globule. The female reproductive body is called nucule. The species of Chara are both types monoecious and dioecious. In monoecious species sex organs are present on adaxial side of the nodes of the primary laterals. The nucule is present above globule on the node. In dioecious species both sex organs are developed separately.
Antheridium or The Globule: - The globule of Chara is a spherical, hollow yellow or red coloured strucure. It is attached to the node of branch of limited growth with the help of pedical. At the centre of the globule the pedical bears 8 primary capitulum cells. The wall of the globule is composed of 8 shield cells which are curved and plate like. Eight elongated rod like cells called manubrium connect the primary capitular cell to middle of the shield cells. Each primary capitulum cell bears six secondary capitula on their cavity face. The secondary capitulum may bear tertiary and quaternary capitula. The last series of capitular cells bear branched or unbranched antheridial filaments. Each antheridium produces a band shaped, spirally coiled and subterminally flagellate antherozoids. At maturity, the shield cells of globule get separated and the antheridial filaments rupture to release the antherozoids.
Ooginium or The nucule: - Nucule is an oval structure having a pedicel cell and unicelled oogonium surrounded by five tube cells coiled in a clockwise direction around it. The oogonium is capped by five celled coronal which are infact the termini of the five cells. In between the pedicel and oogonium lie a small nodal cell and a stalk cell. The oogonium contains a single egg or oosphere. The egg is laiden with starch and oil globules.
Development of sex organs: - Both the sex organs are arise form some divisions of single peripheral cel.
(i) Development of Antheridium (Globule): - The development of antheridium starts from antheridal initial. It devided transversly into basal pedicel cell and terminal antheridial mother cell. There are no division in podicel cell.
Antheridial mother cell spherical and divides by two verticle division. A quadrat is formed but only two cells are visible in a section. All these cells divide transversely and form octant stage of eight cells, of which only four visible. All these cells divide periclinally into eight number of outer cell and the same number of inner cell. The inner cell divide periclinally result is the formation of eight diagonal series of three cells each. There is no division in eight peripheral and eight middle cell. The outermost of peripheral eight cells expand laterally into curved plate and called shield cells. Middle eight form eight rod-shaped manubrial cell.
Manubrial cells developing from the shield cell. At the inner tip of each manubrial cell is persent a primary capitulum cell. Six secondary capitulum develops from each primary capitulum cell. Secondary capitulum cells are about 48 in each globule. Each secondary capitulum cell gives rise to 2-4 long thread like, multicellular branched and unbrabched antheridial filament hundreds of cells are present in each antheridial filaments. These cells function as sperm mother cells and each gives rise to uniunclease and biflagellate antherozoid.
(ii) Development of Oogonium (Nucule): - The upper peripheral cell of the basal node of the antheridium starts to function as oogonial initial. This initial divided to form a short filament of 3 cells. The lower is called pedicel cell, middle one is called cell, Pedicule did not divide, it forms the pedicel of the oogonium.
The oogonial mother cell divides transversely into a lower small stalk cell and upper large oogounium. The oogonium becomes enlarged and its content changed into a single large multinucleate ovum or egg. Single central cell does not divide any further and starts to function as node of oogonium. All five peripheral cells grow upward, elongate and divide transversely into two tiers of five cells. The upper tier of five cells function as coronal cells and lower tier of five cells form tube cells.
Mature nucule: - The ogonium or nucule is oval structure, attached on the node with the help of pedicell cell. It remains surrounded by five long spiraly twisted tube cells. At the top of each which is persent a coronal cell. It contains a single large egg. The nature egg contains a single nucleus.
Fertilization: - Coronal cells spread at the base leaving five small slits at the time of fertilization. Antherizoids enter through these slits swim to oogonium and later penetrate by gelatinising the wall. One antherozoid entering into oogonium fuses with the ovum and form zygote. The zygote secrete a thick wall and becomes oospore.
Oospore and its germination: - It is hard and surrounded by 4 layers. Outer two layers coloured and inner two colourless on ruptureing of oogonial wall the oospore comes out and settle at the bottom of pond.
At the time of germination diploid nucleous divides reductionally, and give six to four haploid nuclei. The oospore divided into two unequal cells by a transverse wall. One nuclei present in upper smaller cell and three in lower larger cell. Three nuclei of lower cell degenerate and upper uninucleate cell project out rupturing the oospore wall. It divides and form a protonemal initial and a rhizoidal initial. Both these initials grow in opposite directions. The rhizoidal initial develops into colourless rhizoid and the protonemal initial develops into an erect primary protonema.