Asexual Reproduction in Chlamydomonas:
When the cell matures, under favorable conditions it multiplies by the formation of zoospores. First, the parent cell comes to rest, and the flagella are cast off or reabsorbed. The contractile vacuoles disappear and the protoplast withdraws from the cell wall as shown below. The cell undergoes a longitudinal division giving two daughter protoplasts. Another longitudinal division giving two daughter cells into four. All the divisions are mitotic. During the division of the protoplast, the chloroplast as well as the pyrenoids also divide. The daughter protoplasts form their own cell wall, and flagella and develop into zoospores. The zoospores liberated into the water by the rupture of the parent cell wall or by the gelatinization of the cell wall. The zoospores later develop into Chlamydomonas cells.
Aplanospore Formation: Chlamydomonas also reproduces asexually by the formation of aplanospores or hypnospores. Thus in C. caudata the whole protoplasm rounds up to form a single aplanospore. In C. nivalis, thick-walled aplanspores (hypnospores) which are colored red due to hematochrome are produced and they cause the formation of red snow in the arctic regions.
Palmella Stage- Under unfavorable conditions, the motile cells come to rest and lose their flagella. The parent cell comes to rest and divides into 4 or 8 daughter protoplasts. The daughter cells do not develop flagella but remain within the gelatinized parent cell wall. Progressive division and re-division of daughter protoplasts followed by the gelatinization of the walls results in a colony of several hundreds of cells embedded in a gelatinous matrix. This aggregation of the cells is known as the Palmella stage as shown below.
Originally when it was first discovered by algologists, they were mistaken for a species of Palmella and hence the name Palmella stage. Exceptionally, in C. kleinii palmella stage is a rule in its life cycle, otherwise it is of rare occurrence in other species of Chlamydomonas. When the damp soil gets flooded with water, the individual cells readily develop their cilia and develop into free-swimming zoospores, which later develop into Chlamydomonas cells.
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