Rhodophyta-2

Organelles

Halydictyon250.jpg (26376 bytes)

Halydictyon sp.- (A Coenocyte) Its Nuclei are Stained with DAPI

Nucleus

Some simple organisms are Uninucleate.

Complex Organisms are Multinucleate (Coenocytic).

There can be 100 to 1000 Nuclei per cell!

They are Eukaryotes and have True Chromosomes. N = 2 - 90

Cell Division & New Wall Organization

The New Cell Wall exhibits Annular Growth.New Wall formation starts from the Outside and proceeds centripetally (towards the center).This is similar to closing an Iris Diaphragm like the Field Diaphragm of a microscope or the diaphragm in a camera lens or in your eye.

A large opening remains between the two cells. A Protein Plug completely blocks cytoplasmic continuity.

This is called the "Primary Pit Connection" and is unique to Rhodophyta.

Chloroplasts

There can be from one to many chloroplasts per cell.

Porphyridium Cell Showing the Chloroplast & Nucleus

Simple Forms have 1 to several.

Larger More Complex Forms have many Small chloroplasts.

Ultrastructure

Chloroplasts have a Double Limiting Membrane with Solitary Thylakoids that are Widely Spaced. This is partly due to the presence of Phycobilisomes which protrude above the surface of the Thylakoids.

Pyrenoids may be present. These have high Concentrations of RUBISCO, the enzyme involved in the Fixation of CO2. Pyrenoids may allow carbon fixation at lower CO2 levels.

The Stroma (matrix) is Homogenous &

Chloroplast of Laurencia

DNA is present.