In this article we will discuss about the vegetative body and reproduction of botrydium.
Vegetative Body of Botrydium (Fig. 75A):
The thallus is unicellular and is differentiated into an upper sub-aerial part and a branched rhizoidal part, which penetrates the soil. The sub-aerial part is globose, pear-shaped or elongated, cylindrical in form, depending on the environmental conditions, and about 1 -2 mm. in diameter. It is surrounded by a tough wall, within which is a peripheral layer of protoplasm surrounding a central vacuole.
The protoplasm contains many nuclei and discoid chromatophores with pyrenoid-like bodies, but oil instead of starch is formed as food-reserve. The rhizoidal portion shows various degrees of branching and is colourless due to the absence of chloroplast. Numerous nuclei are found distributed in the vacuolated cytoplasm. It is evident that within the body of the unicellular alga the protoplasm is continuous throughout, and is characteristic of a coenocyte.
Reproduction in Botrydium:
Botrydium usually reproduces asexually, but sexual reproduction has also been reported in some cases. It is incapable of any vegetative reproduction.
Asexual reproduction takes place by means of zoospores, aplanospores or hypnospores.
When the plants are flooded with water, zoospores ate produced. The protoplasm of the vesicular portion of the plant body, by repeated divisions, forms numerous uninucleate masses which are ultimately metamorphozed into pear-shaped zoospores. Each zoospores possesses anteriorly two flagella of unequal lengths. Due to the gelatinization of the apical portion of the vesicle an opening is formed, through which the zoospores escape and these finally develop into new plants.
When the plants grow in a comparatively dry soil, they form aplanospores. The formation of aplanospores is similar to that of zoospores, but the ultimate protoplasmic masses are either uninucleate or multinucleate, which become rounded and develop a wall around each. Aplanospores, under favourable conditions, germinate directly into new plants.
Thick-walled uninucleate or multinucleate hypnospores may also be formed from the aplanospores of the vesicular portion. In some cases, the protoplasm migrates into the rhizoidal portion and becomes separated into a number of multinucleate, serially-arranged segments, each of which eventually becomes surrounded by a thick wall. Uninucleate hypnospore germinates and directly forms a new thallus. Multinucleate hypnospores, on the other hand, at the time of germination forms a number of zoospores or aplanospores, each of which after liberation forms a new plant.
Sexual reproduction by isogamy has recently been reported. Botrydium is homothallic. Gamete-formation takes place within the vesicle, like zoospore-formation. The gametes usually after liberation fuse in pairs and form a zygote. The zygote germinates immediately. In some cases, parthenospores may also develop from the gametes.
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