Vaucheria
Q.21. Describe the life cycle of Vaucheria with the help of suitable diagram. (1994, 96, 98)
Related Question-
Q. Describe the sexual reproduction in Vaucheria. (2006)
Ans. Systematic position: -
Division - Algae
Class - Xanthophyceae
Order - Siphonales
Family - Vaucheriaceae
Genus - Vaucheria
Occurrence: - They occurs in fresh water in stream spring and water falls with 54 species. Most of the species of Vaucheria are either aquatic or terrestrial. The terrestrial species are found upon damp soil and mud. Rhizoids like branches present in terrestrial species attaching thallus to the substratum.
Thallus structure: - The thallus of Vaucheria is branched, coenocytic unseptate and tubular filament. At the base rhizoidal system is present. The branches have apical growth. In terrestrial forms thallus remains attached to the substratum by rhizoid-like branches with relatively faint colour. This region may be called hepteron. Septation takes place at the time of formation of reproductive bodies.
Cell wall is thin and less elastic. It consists of an inner layer of cellulose and the outer of pectose. A big central vacuole form in the central region of tubular thallus. Cytoplasm is present on the peripheral region. Numerous chloroplast embedded in the cytoplasm towards outside and numerious minute nuclei are found towards central region pyrenoids are present in chloroplast starch grain are absent.
Reproduction: - Reproduction takes place by all three kinds, vegetative, asexual and sexual reproduction.
Vegetative reproduction: - It take place by breaking of thallus into small fragments. This breaking may be accidental. each fragment capable to give rise a new plant.
Asexual reproduction: - Asexual reproduction takes place by several kinds. These are following :
(i) By Zoospores: - A single compound zoospore develops in a single zoosporangium. Any distal branch be act as zoosporangium by separated a cross wall. This separated portion becomes swallen and functions as zoosporangium, chloroplast and nuclei migrate to the distal portion, the contents of the zoosporangium becomes more dense. The entire protoplast contracts and changes into single nucleate and multinucleate zoospore.
(ii) By Aplanospore: - In unfavourable condition an aplanospore develops into an aplanosporangium. Aplanosorangium formed at the apical end of the young branch. Aplanosporangium have a club shaped aplanospore.
(iii) Akinetes: - There are thick walled portion of the filament separated with the help of cross walls. There thick walled, multinucleate parts of the filament are akinetes. Many oil globule are found in protoplasm. This type of asexual reproduction generally found in terrestrial or aquatic species in unfavourable condition.
Sexual Reproduction: - The sexual reproduction in vaucheria is oogamous type place by specialised sex organs anthredia and oogonia.
Antheridium: - The antheridial branch arises as a out growth of the thallus. Many chromatophores and nuclei are present in this outgrowth. It elongates and becomes curved tip. Its terminal curved part is cut off by a septum and this separated part in antheridium. Male gamete or spermatozoids are formed from the entire protoplasm of antheridium
Oogonium: - Oogonium develops near the antheridium in same filament. A colourless multinucleated cytoplasm is accumulated near the antheridium. This colourless mass of cytoplasm called ‘Wanderplasm’ chromatophores are present in wanderplasm.
The oogonial initial enlarges and many chromatophores migrate into it. The oogonium increases in size and becomes rounded septum is formed at the base and the entire rounded. Oogonium is cutoff from the rest of the thallus. The protoplasm content of mature oogonium round off and form a single female gamete.
Fertilization: - Both sexual organs are opening at the time of sexual reproduction. By the opening of the oogonial tip a small drop of cytoplasm comes out in the form of twisted mass. Many spermatozoids comes out from antheridim and get entangled in the cytoplasmic drop of the oogonial liquid. Few of them make way into oogonium. The male nucleus approaches the fema1e nucleus. Fusion of both gametes takes place and results into a diploid zygote or oospore.
Development of Oospore: - After end of the resting period, the diploid nucleus of oospore undergoes meiosis. Haploid nuclei are formed. A new haploid coenocytic siphonous filament emerges from the oospore wall.
