NOSTOC - STRUCTURE OF VEGETATIVE BODY AND REPRODUCTION

-

A. CLASSIFICATION:

Division – Cyanophyta
     Class – Cyanophyceae
          Order – Nostocales
                Family – Nostocaceae
                     Genus – Nostoc
The genus Nostoc comprises about 23 species in India and found to grow both on terrestrial and aquatic habitats. Terrestrial species grow on damp soils, especially in paddy fields and forms lathery or rubbery sheaths (Nostoc commune). Aquatic species are often attached to the substratum or they may be free floating on stagnant water bodies. Some species of Nostoc are also found to live in association with other plant species.
Nostoc thalli occur in colony forming closely packed trichomes. They are enclosed by a common envelop and forms a ball-like structure called ‘Nostoc ball’.
Some of the common Indian Nostoc species are, – N. commune, N. endophytum, N. muscorum, N. hatei, N. punctiforme, N. calcicola, etc.
B. STRUCTURE OF THE VEGETATIVE BODY:
The plant body is un-branched filamentous trichome. The filaments are aggregated together within a mucilaginous envelop forming a ball-like gelatinous colony, known as ‘Nostoc ball’. Nostoc balls are bluish-green or greenish in colour. Each ball or colony contains numerous trichomes which remain inter-winged with each other.
Each trichome is enveloped by a thin mucilaginous, hyaline or coloured sheath forming a filament. Each filament consists of a row of rounded oval cells, which seems to be arranged like beads on a string. Such a habit is called moniliform.
Some cells of the filament are quite larger, rounded and thick walled cells having transparent contents. These are called heterocysts. Besides the formation of heterocysts, the filament occasionally forms akinetes.

C. REPRODUCTION: Nostoc  reproduces entirely asexually by the following methods –
1. Colony Fragmentation:- The Nostoc colony as it gets larger frequently breaks up into flat expanses as a result of storms and other disturbances. Each of these grows into the size of the parent colony.
2. Hormogonia:- Hormogone formation is very common in Nostoc. 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.
3. 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.
**************

Comments

Post a Comment

Popular posts from this blog

EQUISETUM - CLASSIFICATION, STRUCTURE OF SPOROPHYTE, REPRODUCTION, STRUCTURE OF GAMETOPHYTE AND FERTILIZATION

-
Image
A. CLASSIFICATION: Division – Sphenophyta     Class – Sphenopsida        Order – Equisitales            Family – Equisitaceae               Genus – Equisetum Equisetum commonly known as horsetails comprises about 25 species and is world-wide in distribution. Equisetum can grow in wide variety of habitats. Some species grow in damp and shaded places, others grow in ponds and marshes or in sandy soil, near the banks of rivers, etc. Some others are found to grow in exposed dry habitats, along the road side and railway embankments. Some of the common Indian species of Equisetum are – Equisetum debile , E. arvense , E. Diffusum , E. elongatum , etc. B. STRUCTURE OF THE SPOROPHYTE: 1. External structure:- The sporophyte, i.e., the plant body is well differentiated into – stem, leaves and roots – Stem – The stem is underground, horizontal and much branched, which often penetrates more than a meter into the soil. The rhoizome is jointed and provided with nodes and
Read more

SELAGINELLA - CLASSIFICATION, STRUCTURE OF SPOROPHYTE, REPRODUCTION, STRUCTURE OF GAMETOPHYTE, FERTILIZATION, MORPHOLOGY OF RHIZOPHORE OF SELAGINELLA

-
Image
A. CLASSIFICATION: Division – Lycophyta      Class – Lycopsida          Order – Selaginellales              Family – Selaginellaceae                  Genus – Selaginella The genus Selaginella is commonly known as “ Club-moss ” or “ Spike-moss ”. Selaginella is a large genus comprising about 700 species and is world-wide in distribution. Some species of Selaginella are found to grow in temperate regions but majority of them are found to occur in the rain forests of tropical countries. The species of Selaginella is found to grow on the ground, on damp, shaded and humid conditions. Some species are also occurs in arid regions of the world. Temperate species are found to grow on damp shaded sides of the hills. About 55 species are found to occur in India. Of these the common species are S. rupestris, S. chrysocaulos, S. pallidissima, S. jacquemonth, S. megaphylla, S. pentagona , etc. B. STRUCTURE OF THE SPOROPHYTE: 1. External structure:- The sporophyte, i.e., t
Read more

PUCCINIA - CLASSIFICATION, VEGETATIVE STRUCTURE, REPRODUCTION, ECONOMIC IMPORTANCE

-
Image
            A. CLASSIFICATION Division – Mycota       Sub-division – Eumycotina             Class – Basidiomycetes                   Sub-class – Heterobasidiomycetidae                        Order – Uredinales                              Family – Pucciniaceae                                   Genus – Puccinia             The genus Puccinia is cosmopolitan in distribution and is a parasitic fungus causing diseases on many crop plants such as wheat, barley, oats, etc., and causes great loses to the cultivated crops. Puccinia is an obligate fungal parasite and are commonly known as ‘rust fungi’ because they produce ‘rust-like’, i.e., reddish-brown coloured spores in the form of rusty spots or streaks on stems, leaf-sheaths, leaves, etc., of the host plants.             The genus includes about 3000 species. Out of these, 147 species have been reported from India. Wheat rust disease has been extensively studied in India and is found to be caused by three different
Read more