Closterium: Vegetative Body and Reproduction | Algae | Botany

In this article we will discuss about the vegetative body and reproduction of closterium.

Vegetative Body of Closterium:

The body of closterium is strictly unicellular, which is elonga­ted or somewhat lunate without any median constriction, and attenuated at both ends. The cell wall is pro­vided with delicate pores and in most cases with longitudinal striations.

It is mainly made up of cellu­lose and often appears yellowish-brown in colour due to impregna­tion with iron compounds. The cell wall consists of two halves, one belonging to the older genera­tion and the other to the younger one.

They fit so closely and firmly that they are not easily recognizable in living conditions but become se­parated after death or during con­jugation. The protoplast contains two chloroplasts, one within each half of the cell wall and usually with a few pyrenoids. The chloroplasts are either entire or they are provi­ded with radiating longitudinal ridges.

The nucleus lies embedded in a mass of cytoplasm and is connected with the two chloroplasts by means of thin cytoplasmic strands. At the attenuated ends (poles) of each cell there is a conspicuous vacuole in which is embedded one or more crystals of gypsum salts.

Reproduction in Closterium:

Closterium reproduces vegetatively as well as by the sexual method.

During vegetative reproduction there is a transverse division of the pre-existing nucleus and the two chloroplasts. It is very peculiar that in this case the dividing wall is not formed in the middle of the cell but a little away from the centre and within the younger half wall of the cell.

Sexual reproduction takes place by conjugation of amoeboid gametes from two conjugating cells. In some cases, a rudimentary conjugation tube may be formed between them; in others, sister cells probably conjugate. In most cases, the cell wall breaks in the middle region (isthmus) and its protoplast escapes as an amoeboid gamete, which, on finding its mate, unites with it and forms a spherical, ovoid or quadrangular zygote (zygospore) with thick or ornamented walls.

After the resting period the zygote germinates, its nucleus divides reductionally forming four daughter nuclei, of which two degenerate. This is followed by the division of the pro­toplast, each of which contains a single chloroplast, a functional and a disintegrating nucleus. The daughter protoplast sooner or later surrounds itself with a cell wall and assumes the shape cha­racteristic of the genus.