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In this article we will discuss about the general characteristics of plasmodiophoromycetes.
The representatives of this class are obligate endoparasites of the seed plants (Cabbage, Nasturtium), ferns (Azolla), algae (Vaucheria) and Fungi (Achlya, Saprolegnia). The somatic phase is a moving, naked, multinucleate mass of protoplasm feeding in an amoeboid fashion.
It is known as the Plasmodium. It grows within the host cells and is holocarpic. Two types of plasmodia namely primary or gametangial plasmodia and secondary or cystogenous Plasmodia occur in the life cycle. The former are haploid and the latter diploid.
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The entire protoplasm of the primary Plasmodium divides to give rise to thin-walled gametangia, each of which contains a single motile biflagellate, uninucleate structure which functions as a gamete. In older terminology, it is called a zoospore and the Plasmodium bearing it as zoosporogenous Plasmodium.
The cystogenous Plasmodium divides by meiosis to form thick- walled resting meiospores. Some scientists call them resting sporangia or cyst. On germination each cyst gives rise to a zoospore or cyst zoospore. Both the gametes and the cyst zoospore are uninucleate, biflagellate and similar in structure.
Both the flagella are of whiplash type but of unequal length (heterokont) and inserted anteriorly, the shorter near the longer one. The longer flagellum terminates in an end piece. The shorter flagellum lacks the end piece. It has blunt tip. When the swarm cell is in motion, the longer flagellum trails behind and the short blunt flagellum is directed forward.
The nuclear division occurring during the somatic phase of both gametangial and cystogenous phases is cruciform. Sexual reproduction when present is isogamous and takes place by planogametic copulation. The class includes a single order Plasmodiophorales.
