In this article we will discuss about the Structure of Cyanobacteria (Blue Green Algae).
Blue-green algae are the most primitive organisms in the plant kingdom and show typical prokaryotic organization (Fig. 1.13).
A typical cell of blue-green algae is composed of the following components:
1. Outer cellular covering.
3. Nucleic material.
1. Outer Cellular Covering:
The outer covering of cell includes:
(a) Mucilaginous layer
(b) Cell wall and
(c) Innermost plasma membrane.
(a) Mucilaginous layer:
Mucilaginous sheath is the outermost layer covering the cell wall. In some cases the mucilaginous layer is very conspicuous and forms mucilaginous sheath but in others it may be inconspicuous. It protects the cell from the injurious factors of the environment.
(b) Cell wall:
Just below the mucilaginous layer is present cell wall. Electron microscopy has revealed that the cell wall is relatively complex structure. The cell wall is 2 or 3-layered and the inner layer lies in between outer wall layer and plasma membrane. The cell wall is formed of polysaccharides and mucopeptides.
(c) Plasma membrane:
The plasma membrane is selectively permeable living membrane enclosing the cytoplasm and is lipoproteinic in nature.
Below the plasma membrane is seen the groundplasm which contains structures of different shapes and functions. In the peripheral region of cytoplasm are located lamellae which contain pigmemts (Fig. 1.14). Fine structure study has made it clear that the pigmented lamellae are not organised into plastid. Lamellae or membranes are derived from plasma membrane.
The pigments in lamellae include chlorophylls, carotenes, xanthophylls, c-phycoerythrin and c-phycocyanin, the last two are characteristically found in blue-green algae only. In addition to lamellae, several membrane bound vesicles may also be seen in the cytoplasm and they may sometimes be stacked in layers. Besides, ribosomes may be found scattered in the groundplasm.
3. Nuclear Material:
The nucleoplasm or DNA containing region is centrally located in the cell and shows a fibrillar structure. Nucleoplasm is feulgen- positive but is not organised into an electron micrograph of cell, nucleus, i.e., there is no nuclear boundary and no nucleolus. During division the nucleoplasmic material dispersed throughout the cell divides into two and no spindle apparatus participates in this process.