Describe various methods of asexual reproduction in algae
Asexual Reproduction:
Asexual reproduction involves the formation of certain type of spores — either naked or newly walled. It is a process of rejuvenation of the protoplast without any sexual fusion. Each and every spore germinates into a new plant. In this method, there is no alternation of generations.
The asexual spores may be of various types:
a. Zoospores:
These are motile naked spores provided with two, four or many flagella and called as bi-, quadri- or multiflagellate zoospores, respectively. Biflagellate zoospores are found in Chlamydomonas, Ulothrix Ectocarpus etc., quadriflagellate zoospores are found in Ulothrix and multiflagellate zoospores are found in Oedogonium
But the multinucleate and multiflagellate zoospores as found in Vaucheria (Fig. 3.17D) are called synzoospores. Each zoospore has a chloroplast and an eye spot. The zoospores may be either haploid or diploid.
Asexual Spores in Algae
They are formed within the zoosporangium. There may be single zoospore (e.g., Oedogonium) or many zoospores (e.g., Cladophora) per zoosporangium. Zoospores are either haploid or diploid depending on the nature of plant body, gametophytic or sporophytic on which it develops.
The zoospores are liberated either by the disintegration of the zoosporangial wall or by the formation of an apical pore on the zoosporangium. After liberation the zoospores swim for a while, then withdraw their flagella, encyst and ultimately germinate into new plants.
b. Aplanospores:
Aplanospores are non- motile spores. These spores are formed either singly or its protoplast may divide to form many aplanospores inside sporangium during unfavourable conditions, especially in drought (e.g., Ulothrix Microspora). The aplanospores may also be formed in certain algae of semiaquatic habitat.
When they appear identical to the parent cell, they are referred to as autospores (e.g., Scenedesmus, Chlorella etc.). Aplanospores with thickened wall and abundant food reserve are known as hypnospores (e.g., Pediastram, Sphaerella etc.).
They are formed to overcome prolonged period of desiccation. With the onset of favourable condition the hypnospores either directly germinate into a new individual or their protoplasts may form zoospores. Due to deposition of haematochrome pigment in their walls, the hypnospores of Chlamydomonas nivalis are red in colour.
c. Tetraspores:
Diploid plants of some algae (e.g., Polysiphonia, ) produce a special type of haploid aplanospores, called tetraspores, formed within tetrasporangium. The diploid nucleus of a tetrasporangium divides meiotically to form four haploid nuclei which — with little amount of protoplasm — are developed into four tetraspores. After liberation the tetraspores germinate to form male and female gametophytes.
d. Akinetes:
The vegetative cells of certain filamentous algae develop into elongated thick-walled spore-like structures with abundant food reserves, called akinetes (e.g., Gloeotrichia, ). They can tide over the unfavourable conditions. With the onset of favourable condition they germinate into new individuals.
e. Exospores:
In some algae, spores are regularly cut off at the exposed distal end of the protoplast in basipetal succession, called exospores. These spores aggregate in groups and develop new colonies, e.g., Chamaesiphon
f. Endospores:
These are small spores formed by the divisions of the mother protoplast. They are also called conidia or gonidia. They are set free after the dissolution of mother wail. Without taking rest, the spores germinate directly and develop into a new plant, e.g., Dermocarpa
Asexual reproduction involves the formation of certain type of spores — either naked or newly walled. It is a process of rejuvenation of the protoplast without any sexual fusion. Each and every spore germinates into a new plant. In this method, there is no alternation of generations.
The asexual spores may be of various types:
a. Zoospores:
These are motile naked spores provided with two, four or many flagella and called as bi-, quadri- or multiflagellate zoospores, respectively. Biflagellate zoospores are found in Chlamydomonas, Ulothrix Ectocarpus etc., quadriflagellate zoospores are found in Ulothrix and multiflagellate zoospores are found in Oedogonium
But the multinucleate and multiflagellate zoospores as found in Vaucheria (Fig. 3.17D) are called synzoospores. Each zoospore has a chloroplast and an eye spot. The zoospores may be either haploid or diploid.
Asexual Spores in Algae
They are formed within the zoosporangium. There may be single zoospore (e.g., Oedogonium) or many zoospores (e.g., Cladophora) per zoosporangium. Zoospores are either haploid or diploid depending on the nature of plant body, gametophytic or sporophytic on which it develops.
The zoospores are liberated either by the disintegration of the zoosporangial wall or by the formation of an apical pore on the zoosporangium. After liberation the zoospores swim for a while, then withdraw their flagella, encyst and ultimately germinate into new plants.
b. Aplanospores:
Aplanospores are non- motile spores. These spores are formed either singly or its protoplast may divide to form many aplanospores inside sporangium during unfavourable conditions, especially in drought (e.g., Ulothrix Microspora). The aplanospores may also be formed in certain algae of semiaquatic habitat.
When they appear identical to the parent cell, they are referred to as autospores (e.g., Scenedesmus, Chlorella etc.). Aplanospores with thickened wall and abundant food reserve are known as hypnospores (e.g., Pediastram, Sphaerella etc.).
They are formed to overcome prolonged period of desiccation. With the onset of favourable condition the hypnospores either directly germinate into a new individual or their protoplasts may form zoospores. Due to deposition of haematochrome pigment in their walls, the hypnospores of Chlamydomonas nivalis are red in colour.
c. Tetraspores:
Diploid plants of some algae (e.g., Polysiphonia, ) produce a special type of haploid aplanospores, called tetraspores, formed within tetrasporangium. The diploid nucleus of a tetrasporangium divides meiotically to form four haploid nuclei which — with little amount of protoplasm — are developed into four tetraspores. After liberation the tetraspores germinate to form male and female gametophytes.
d. Akinetes:
The vegetative cells of certain filamentous algae develop into elongated thick-walled spore-like structures with abundant food reserves, called akinetes (e.g., Gloeotrichia, ). They can tide over the unfavourable conditions. With the onset of favourable condition they germinate into new individuals.
e. Exospores:
In some algae, spores are regularly cut off at the exposed distal end of the protoplast in basipetal succession, called exospores. These spores aggregate in groups and develop new colonies, e.g., Chamaesiphon
f. Endospores:
These are small spores formed by the divisions of the mother protoplast. They are also called conidia or gonidia. They are set free after the dissolution of mother wail. Without taking rest, the spores germinate directly and develop into a new plant, e.g., Dermocarpa