ANABAENA - STRUCTURE OF VEGETATIVE BODY AND REPRODUCTION

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A. CLASSIFICATION:
Division – Cyanophyta
     Class – Cyanophyceae
          Order – Nostocales
                Family – Nostocaceae
                     Genus – Anabaena
The genus Anabaena comprises about 23 species. It is a fresh water alga and is found to float in water of rice fields, ponds, pools, etc. The filament of the species lives singly without forming a colony. Some species of Anabaena are endophytic living in the root tubercles of Cycas sp. and leaves of Azolla sp.
Some of the common Indian species of Anabaena are – Anabaena cylindrica, A. variabilis, A. fertillissima, A. gelatinicola, A. sphaerica, A. oscillariodes, etc.
B. STRUCTURE OF THE VEGETATIVE BODY:
The plant body is un-branched filamentous trichome. Usually the trichomes are straight, but may be twisted in some planktonic species.
              Each trichome possess an extremely watery i.e., hyaline gelatinous sheath forming a filament. In some species the trichomes are devoid of mucilaginous sheath. Each trichome consists of a string of beaded cells. The cells are usually barrel shaped or spherical, but never discoid. Some of the cells in the filament are possess thick walls, and are called heterocysts. Akinetes, the larger cells, also known as resting spores are also present on both the sides of the heterocyst.
C. REPRODUCTION: Anabaena  reproduces entirely asexually by the following methods –
1. Hormogonia:- Hormogone formation is very common in Anabaena. In such case the trichome ruptures at places where heterocyst and the vegetative cells adjoin. In this way short, short segments of living cells are formed called the hormogonia.
The hormogonia slip out of the gelatinous matrix and establish new colonies by division. The terminal cells of the hormogonia differentiate into heterocysts. The intercalary cells then divide in the plane parallel to the axis of the trichome forming a packet of cells. This is called aseriate stage.
2. Akinetes:- Under certain conditions any cell or some vegetative cells of the trichome become enlarged and secretes a thick, highly resistant wall around it. They get filled with the reserved food materials. Such specially modified vegetative cells are called akinetes or resting spores. These are well adapted to survive the unfavourable conditions like water shortage and unsuitable temperature.
             The resting spores survives during the unfavourable conditions and with the return of the favourable conditions, they germinate into new plants.
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Comments

  1. UnknownDecember 27, 2020 at 8:05 AM

    Nonsense is this the place to write these things... Is this what u are taught .

    ReplyDelete
  2. UnknownDecember 9, 2021 at 6:15 AM

    I landed on this site when I was learning about nitrogen fixing freshwater species.

    I would like to know more.

    ReplyDelete

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