Described first by Camillo Golgi in 1890 in the nerve cells of barn owl, the Golgi complex has attracted the attention of cell biologists not only by its complex structure but also by its varied functions.
In fact Golgi complex was observed earlier by St George in 1865 itself. Nassonov (1923) and Bowen (19229) established the secretary function in the Golgi apparatus.
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1. Terminoloy:
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Various terms have been employed to refer to the Golgi complex. Baker (1953) described them as Lipochondria as they have high lipid content. Golgi complex found in plant cell is often refered to as Dictyosomes.
2. Occurrence and distribution:
All the eukaryotic cells have a golgi complex which is absent in prokaryotic cells. Even in eukaryotic cells of some fungi, spenrmatozoids of bryophytes etc. golgi complex is absent.
3. Distribution:
In higher plants, golgi complex is scattered all over the cytoplasm apparently without any localization (Hall 1974). As a contrast in animal cells, the golgi complex is localized into an organelle. In animal cytoplasm, usually there is only one golgi apparatus, but in some cases as in Storeomyxa there may be many complexes.
In shape, the Golgi complex is variable depending on the cell type; it varies from a compact mass to dispersed filamentous reticulum. In size, the golgi complex varies from large (nerve cells.) to small (muscle cells).
4. Morphology:
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The morphology is variable depending on the source. In plants the golgi bodies are about I – 3nm in length and 0.5nm thick. Each golgi body consists of the following parts – cisternae, tubules, vesicles and golgian vacuoles.
The cisternae are flattened sacs filled with a fluid. Each golgi body consists of 4 – 8 flat structures which are slightly curved and are arranged in stacks. Each cistema is enclosed by the trilaminar membrane 6nm in thickness and is separated from the other by a 100 -150A wide space.
In some instances the intercisternal space is filled by fibres called intercisternal elements. The membranes of the cisternae are fenestrated (porous). The pores may be localized or present all over the cisternae. Occasionally cisternae may form reticulate structures.
5. Tubules:
Arising from the peripheral region of the cisterane, the tubules form an anastomosing network of300 – 500A in diameter.
6. Vesicles:
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These are goblet like structures attached to the tubules. There are two types of vesicles smooth vesicles and coated vesicles. The smooth vesicles are 20 – 80nm in diameter and are often called secretory vesicles. These are pinched off from the ends of cistetnal tubes. The coated vesicles are spherical outgrowths about 50nm in diameter. The function of the coated vesicles is not known.
7. Vacuoles:
These are large spaces occurring at the distal end of the cisternae. They represent the cistemae whose membranes are widely separated.
In the case of Dictyosomes (isolated golgi bodies) of plants, cistemae are extensively fesnestrated and have rough and smooth vesicles attached to them. Parallel fibres fill the intercisternal place.
8. Chemical composition of golgi complex:
Proteins and phospholipids are in equal concentration. Golgi material in the nerve cells consists of cephalin and lecithin. Giroud has reported Vitamin C in the golgi complex.
9. Functions of the golgi complex:
The following are some of the functions attributed to the golgi complex –
1. Absorption of compounds
2. Sites of enzyme production
3. Sites of hormonal production
4. Sites of protein storage
5. Forms acrosome during sperm maturation
6. Forms intracellular crystals
7. Formation of plant cell wall – the golgi bodies synthesise pectin, hemiceullulose and cellulose microfibrils. They also help in the formation of cell plate during mitosis.
10. Origin of golgi complex:
Evidences indicate that the golgi bodies are produced from the membranes of the smooth ER. Earlier it was thought that they arise de novo or from the phragmoplasts of the cell wall. Both these theories are found to be incorrect.