This document summarizes the distribution, systematic position, and life cycle of the cyanobacteria Nostoc and the charophyte alga Chara.
Nostoc is a terrestrial or aquatic cyanobacteria that grows in gelatinous colonies of trichomes containing vegetative cells, heterocysts, and akinetes. It fixes atmospheric nitrogen and reproduces through hormogonia formation or budding.
Chara is a submerged freshwater charophyte alga that attaches to substrates via rhizoids. It has a branched thallus with nodes bearing short branches, stipulodes, and longer axillary branches. It reproduces vegetatively through amylum stars and bulbils or
4. Distribution and features:
• Terrestrial and aquatic habitats
• Grows in large colonies of closely packed trichomes –
embedded in gelatinous material.
• Colour – olive green or blue-green
• Terrestrial – grows on damp soil
• Aquatic – free floating or lie at bottom attached to
submerged vegetation
• Fix atmospheric nitrogen – maintain soil ferility
5. • Structure
• Trichome – enclosed by mucilaginous sheath – filament
• Composed of numerous cells joined like string of beads
• Heterocyst – colourless, empty-looking, barrel shaped cells – slightly larger
and thicker than vegetative cells – intercalary or terminal
• Akinetes – resting bodies stored with food materials
6. Life cycle:
1. Heterocystous phase - a) motile hormogonia; b) non
motile hormogonia with terminal heterocysts and
enveloped in a hyaline sheath; c) aseriate colonies
formed by several divisions occurring in different
planes. At the beginning the colony is elongated, then
it becomes spherical and contains a coiled filament
formed by vegetative cells and heterocysts; d)
reproduction of the colony by hormogonia or budding.
Buddings are more frequent in cultures grown on solid
medium. The hormogonia also are formed by a
breaking of the colonial filament at the junction of the
heterocysts and are released by rupture or dissolution
of the colony sheath; e) vesicles of transparent
mucillage containing numerous isolated hetercysts
after the release of the hormogonia.
2. Sporogenous phase – light exposure – 2 to 4 celled
fragments, grow to form long trichomes without
heterocysts, trichomes break into fragments,
intercalary cells develop into spores, spores germinate
– form 2-3 celled germlings
8. Distribution and features:
• Submerged aquatic alga – attach to soft mud at the bottom
• Prefers fresh, hard and shallow water
• Species growing in water containing calcareous materials
become encrusted by calcium carbonate
• Thallus organization:
o Rhizoids – for attachment to the substratum
o Has upright branched axis – short nodes and long internodes
o Node:
1. Branchlets – short branches of limited growth (primary
laterals)
2. Long branches – branches of unlimited growth (axillary
branches)
3. Stipulodes – unicellular outgrowths arise from node
9.
10. • Life cycle:
• Vegetative reproduction – amylum stars (star-shaped cell aggregation on
nodes), bulbils (rounded tuber-like structures on rhizoids)
• Sexual reproduction – oogamous - antheridia (globule), oogonia (nucule)
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12.
13. References
• Vashishta B.R., Sinha A.K. and Singh V.P. 2012. Botany for
degree students: Algae. S. Chand & company ltd.
• Fritsch, F.E.,(1956). The structure and reproduction of the
Algae; Volume I and II. Cambridge University Press.