Sexual reproduction in Spirogyra

In spirogyra, sexual reproduction takes place by conjugation. The fusion process of two opposite strains (positive, negative) cells is called conjugation. Male having a positive strain and female having a negative strain or fusion process of two isogametes called conjugation. Zygospore is the final product of conjugation. In spirogyra, conjugation is of two types:

• Scalariform conjugation
• Lateral conjugation

Scaliform conjugation

It involves in between two filamentous cells. It is a common type of conjugation in spirogyra. Most of the species of spirogyra sexually reproduce by the scalary form of conjugation.

During conjugation period, two conjugating filaments come close to each other and grow parallel. Two conjugating filaments are connected by mucilage layer. Between two filamentous cells, outgrowth like structure appears called protuberance. Continuous growth of protuberance joins together with two filamentous cell called conjugation tube formation. In scalariform conjugation, one whole filamentous cell function as a male and another function as a female. After conjugation tube formation, the protoplasmic mass of the male cell function as male gamete and protoplasmic mass of the female cell rounded to form female gamete.

The male is active and donor. It moves towards the female through conjugation tube. Fusion product of male and female cell is called zygote. It secretes thick-walled zygospore so, in scalariform conjugation male filamentous cells are empty and female filamentous cells are filled with zygospore. Due to the several conjugation tube formation between two filamentous cells, its appearance is like a ladder. So, it is also called ladder like conjugation.

Lateral conjugation

In lateral conjugation, a single filament is involved. During conjugation period, adjacent cells of the same filament function as a male and female. Fusion product of male and female cell is diploid zygospore. In lateral conjugation, the male cell is empty and female cell is zygospore. Lateral conjugation is of two types;

• Indirect lateral conjugation
• Direct lateral conjugation

Indirect lateral conjugation

Spirogyra affinis sexually reproduce by indirect lateral conjugation. During conjugation period adjacent cells of the same filament function as a female and male. Between two conjugating cells, conjugation tube is formed. After conjugation tube formation, the protoplasmic mass of the male cell rounded to form male gamete and protoplasmic mass of female cell rounded to form female gamete. The male is active and donor. It moves towards the female through conjugation tube. Fusion product of male and female cell is called diploid zygospore.

Direct lateral conjugation

Spirogyra genesis sexually reproduces by direct lateral conjugation. During conjugation period, the protoplasmic content of the male cell rounded to form male gamete and protoplasmic content of female cell rounded to form female gamete. Male move towards the female by the formation of a septal pore. Fusion product of male and female cell is diploid zygospore.

Germination of zygospore

Zygospore is the final product of conjugation. It is diploid, thick walled structure surrounded by three different layers. The outer smooth layer is exine. The middle layer is called mesine and the innermost covering layer is called intine. Zygospore contains a diploid nucleus, degenerating chloroplast, and dense cytoplasm. After liberating from mother filamentous cell, it undergoes meiosis cell division and produces four haploid nuclei. Out of four three haploid nuclei are degenerate. One of the functional haploid nuclei germinates to form a young filament of spirogyra.