In 1898, Camillo Golgi, an Italian neurobiologist, discovered a reticulate structure in the cytoplasm of nerve cell of an owl. This organelle is known as Golgi complex, Golgi apparatus, Golgi body or dictyosomes. This is usually present in all eucaryotic cells, but is absent in prokaryotic cells. But, so far, Golgi complex is not reported in cells of fungi, male gametes of bryophytes and pteridophytes, mature sieve tubes and RBC.
Golgi complex is a major cytoplasmic organelle that measures about 1-3 u in length and about 0.5u in height. The shape and size of the complex are variable depending upon the type of cells where it is present. The number of Golgi complex varies from only one in certain alga to about 25,000 in a generalised plant cell. The complex consists of one or more stacks of flat, discoid, parallel inter-communicating cisternae. A cisternae is a fluid filled lumen of about 60-90 Å across, enclosed by a single smooth membrane of 60-70 Å thick. In a plant cell, 2-7 such cisternae constitute one Golgi apparatus.
There is continuity between adjacent cisternae and they do not possess a common boundary. The periphery of this cisternae highly branched giving rise to an anastomosing network of tubules whose diameter varies from 300-500 Å. End points of cisternae constitute a number of vesicles which are pinched off from the smooth endoplasmic reticulum and fuse with the Golgi cisternae through transitional vesicles.
Golgi complex forms an extensive intercommunicating network of membranes in association with a cell membrane, endoplasmic reticulum, lysosome and nuclear membrane. They form the endomembrane system of the cell as they seem to have a common origin and are closely associated. Some regions of endomembrane system constituting of more Golgi complex are often called GERL (Golgi-Endoplasmic reticulum-Lysosome complex). The lumens of endoplasmic reticulum and Golgi cisternae communicate with each other forming passages for transport of secretory proteins, lipids and sterols. The membranes of Golgi cisternae and endoplasmic reticulum are also continuous with each other, thereby allowing the onward flow of membrane proteins and lipids along the membranes.
Secretion is the main function of Golgi complex. The vesicles packed with the secreted proteins and lipids are pinched off from the dilated tips of cisternae into the cytoplasm as secretory or zymogen granules. These granules ultimately release their contents by exocytosis. Besides, the Golgi complex participates in the recycling of plasmamembrane. Synthesis of pectins and other carbohydrates, necessary for cell wall formation, are done by Golgi complex. It also secrets gum and mucilage.