NUCLEUS
- Nucleus was first discovered by Robert Brown (1831) in orchid cells.
- It is the most important part of the cell which directs and controls all the cellular functions.
- That’s why the nucleus is very often regarded as ‘director of the cell’.
- Presence of a true nucleus with nuclear membrane and linear chromosomes is the characteristic of all the eukaryotic cells.
- However, there are some exceptions viz., mature mammalian RBCs, sieve tubes of phloem, tracheids and vessels of xylem.
- As far as the number of nuclei in a cell is concerned, most eukaryotic cells have a single nucleus within them.
- However, the number may vary in some cells.
- Depending on the number of nuclei cells may be of following types :
- Anucleate (without nucleus) : Mammalian RBCs.
- Uninucleate : Most Eukaryotic Cells.
- Binucleate : Basidiomycetes, Paramoecium
- Multinucleate : Phycomycetes like Mucor, Rhizopus etc.Red Algae.
- The true Nucleus may be defined as: ‘The cellular structure limited externally by a nuclear membrane surrounded by cytoplasm which contains linear nucleoproteinous chromosomes and carry genetic information from generation to generation’.
- The carrier of genetic information about the nature of nuclei was established by Hammerling (1953) who worked on the macroscopic unicellular alga, Acetabularia and concluded that the morphology of the plant is solely determined by the type of nucleus contained in the plant body.
