Algae are of great use and the branch of study that deals with the detailed description of the functioning and livelihood of algae is termed as “microbiology”. Algae are organisms with specialized multicellular reproductive structures of plants. These organisms do not contain any true roots, shoots or leaves. These eventually are known predominantly for their aquatic, photosynthetic and nucleus-bearing organisms.
Let us discuss one of the living organisms which cannot be seen with naked eyes and are microscopic which is a yellow-green algae named vaucheria in detail .
Vaucheria is a green freshwater alga found in lakes, canals and wetlands and It will not float freely like spirogyra but it is attached to the substratum with colorless rhizoids or holdfasts. The thallus is a single tubular cord. It contains nuclei (minute) in the living layer of the cytoplasm around a large central vacuole. Such a structure is called a coenocytic in which septa appear in the connection with reproductive organs.
The Life Cycle of Vaucheria
According to Williams, Handtasche and Gross, the life cycle of vaucheria is haplontic, only oospore is the diploid structure in the life cycle. Vaucheria thallus is haploid, Aseptate, branched, tubular and coenocytic structure. In vaucheria vegetative reproduction, occurs by fragmentation, and asexual reproduction occurs by zoospores in aquatic and alpanospores in terrestrial.
Vaucheria Reproduction
Reproduction in vaucheria occurs by all three means, vegetative, asexual and sexual reproduction. Vegetative reproduction in vaucheria occurs by the accidental breakage of the vegetative filament, in which septa are formed in the injured region of the filament.
Asexual Reproduction
There are various means of asexual reproduction in vaucheria. Some of the reproductive structures of vaucheria are mentioned below –
(a) Zoospores,
(b) Aplanospores
(c) Hypnospores,
(d) Cyst formation.
(a). Zoospores
In vaucheria, asexual reproduction occurs by the large solitary zoospore, during the period of development, the apex of the filament swells up and becomes club-shaped, further, it will be separated from the rest of the filament by septum. The club-shaped body formed is called Zoosporangium. The protoplasmic content of the zoosporangium, makes it rounded off forming a single zoospore wall of zoosporangium, that ruptures at the apex and zoospore escapes from the terminal pore and begins to rotate. The shape of the zoospore is oval and large in size, the central part of it is occupied by a large vacuole and is surrounded by the zone of protoplasm.
Many small chloroplasts lie there, which gives green color to the zoospore. The complete surface of the zoospore is covered with many short cilia arranged in pairs and under each pair lies a nucleus, therefore the zoospore is regarded as one compound. Zoospores after escaping, swims freely in water, with the help of cilia and soon comes to rest. Further, after coming zoospores to the rest, it germinates and produces colorless branches rhizoid and that attaches the branch of the substratum.
(b) Aplanospores
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Aplanospores produced at the edges of the last branches are known as aplano sporangia.
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Aplanospores are usually produced by earthly species.
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It is non-motile in nature with thin-walled spores.
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They may be round or elongated in shape.
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One aplanospore is formed in each aplano sporangium.
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Sexual Reproduction
In vaucheria, asexual reproduction takes place by the method of fertilization, with the help of sharply differentiated male and female reproductive organs. The male reproductive organ is known as antheridia and the female reproductive organ is known as oogonium, they are developed at a scattered interval of time after lateral outgrowths.
The oogonium formed during outgrowth swells out, assumes to be a more or less rounded form and is cut off by basal septum. The apex of the oogonium developed, either breaking towards antheridium or away from it, and the protoplasm of the oogonium contains one nucleus, which forms the single large female gamete egg (ovum or oospores) which fills the oogonium. Each antheridium arises with the short tubular branch by the side of the oogonium and the terminal portion of it is cut off by a septum then it becomes actual antheridium. Once the antheridium becomes matured, it is much curved towards the oogonium. The protoplasm contains multiple chloroplasts and nuclei, many of the male gametes (antherozoids) are produced inside the antheridium, and they are minute in size and are bi-ciliated, cilia point in the opposite direction.
Fertilization
Self-fertilization is common but in dioecious species cross-fertilization is present. Antheridium bursts at the apex and many antherozoids call around the beak which opens at about the same time. Many antherozoids enter the oogonium through the break, but only fuse with the ovum, while all others perish. Once the fertilization is done, the ovum becomes invested with a thick cell wall called an oospore, undergoes a period of rest and germinates into a new vaucheria filament.
Vaucheria Classification –
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Phylum: Ochrophyta
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Class: Xanthophyceae
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Order: Vaucheriales
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Family: Vaucheriaceae
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Genus: Vaucheria
Vaucheria is sometimes also classified into the groups of Chlorophyceae. This is because the organism also contains different types of chlorophyll in its body. It contains chlorophyll a, chlorophyll e, carotenoids and xanthophylls. Even the amount of carotenoids in the vaucheria body is much higher than chlorophyll contains.
Selected species are:
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Vaucheria borealis
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Vaucheria disperma
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Vaucheria geminata
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Vaucheria hercynian
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Vaucheria litorea
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Vaucheria sessilis
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Vaucheria terrestris
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Vaucheria woroniniana
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Vaucheria jonsai
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Vaucheria hemata
Important Features of Vaucheria
1. Plant body is filamentous, coenocytic and branched. It remains attached to the substratum by rhizoids.
2. Reserve food is fats and oils.
3. Reproduction takes place by all three means: Vegetative, Asexual and Sexual.
4. Vegetative reproduction takes place by fragmentation.
5. Reproducing asexually in vaucheria, occurs by combining multi-flagellate zoospores (syn zoospores ), aplanospores, hypnospores and akinetes.
6. Sexual reproduction is oogamous.
7. The oogonium of vaucheria contains one large, uninucleated egg, while the antheridium contains several biflagellate antherozoids.
8. Oospore or zygote undergoes meiosis during germination and forms a new plant, Vaucheria.
Did You Know?
How does vaucheria differ from the other members of the Chlorophyceae? There was a great controversy regarding the taxonomic status of Vaucheria classification. Fritsch (1935) included Vaucheria along with the other three genera (Vaucheriopsis, Dichotomy Siphon and Pseudo Dichotoma Siphon) in the family Vaucheriaceae under the class Chlorophyceae. Because some of the characteristics were different, some of them are mentioned below
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Absence of mercerized cellulosic cell wall.
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Absence of pyrenoid.
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Paired flagella of syn zoospores are unequal.
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Absence of chlorophyll b.
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Reserve food is oil