Cellular Alime Moulds Habitat and Life Cycle, Myxamoebae, Uninucleate, Haploid, Amoeba Like, Formation of Pseudoplasmodium, Communal Slime Moulds

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Cellular Slime Moulds Habitat

The cellular slime moulds occur in all humus-containing upper layers of damp soil.

Life cycle of Cellular Slime Moulds

Life cycle (Fig. 6.3) of a typical cellular slime mould includes the following:

(i) Myxamoebae. These are uninucleate, haploid and amoeba-like cells. Myxamoebae are without cell wall. They are covered by plasma membrane. They move by amoeboid movements. Myxamoebae feed on bacteria and other microorganisms through ingestion (phagotrophic or holotrophic nutrition).

They grow and divide to form a large population of individuals. Under unfavourable conditions, a myxamoeba secretes a rigid cellulose wall to form the microcysts. Microcyst formation is a means of perennation. The microcysts can be dispersed.

On the return of favourable conditions, the microcyst wall ruptures to release a myxamoeba. The latter resumes its function of feeding, growth and multiplication forming amoeboid cells.

(ii) Formation of Pseudoplasmodium.

When the food supply is exhausted, the amoeboid cells get aggregated without any fusion.

The stimulus for the aggregation process is due to release of cyclic 3',5' adenosine monophosphate (cyclic AMP) from the amoeboid cells.

This aggregated mass of cells is called pseudoplasmodium. It is a sort of community association. Because of this reason, cellular slime moulds are called the communal slime moulds.

Significance of Pseudo plasmodium.

The pseudoplasmodium exhibits a primitive form of multicellularity, where cells maintain their identity but can live together. It also shows division of

Life Cycle of a Typical Cellular Slime Mould

1. Division	6. Spore
2. Amoeboid Cells	7. Sporangium
3. Pseudo Plasmodium	8. Stalk
4. Myxamoeba	9. Substratum
5. Spore Germination

labour as some cells form fruiting body (sporangium) while others form spores. For this reason the cellular slime moulds are regarded as advanced protists or primitive fungi.

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(iii) Formation of Sporangium.

The aggregated cells of pseudoplasmodium differentiate and migrate to form a stalked sporocarp. The sporocarp bears a sporangium at its terminal end.

The sporangium of cellular slime moulds is naked. The stalk may remain upright or become slightly bent.

(iv) Formation of Spores.

The cells present inside the sporangium become rounded and become surrounded by the cellulose wall to form the spores.

Each spore is an void, haploid, uninucleate mass of protoplast covered by a cellulose cell wall. The spore germinates to produce a single naked amoeba-like cell called myxamoeba.

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Sexual Reproduction.

In this process, the myxamoebae form clusters. The central myxamoeba of the cluster engulfs a surrounding myxamoeba to become larger structure which forms a thick wall to form the zygote.

This zygote is called macrocyst. Karyogamy occurs inside the macrocyst which is followed by meiotic and several mitotic divisions.

Ultimately the macrocyst wall ruptures to release a number of haploid myxamoebae.

Examples of Cellular Slime Moulds are: Dictyostelium, Polysphondylium.

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