CELL SUICIDE OR PROGRAMMED CELL DEATH

M. Elsahookie, M.; W. Abdalqahar, F.

	CELL SUICIDE OR PROGRAMMED CELL DEATH
The Iraqi Journal of Agricultural Science
Article 1, Volume 40, Issue 3, 2009, Pages 1-26
Authors
M. M. Elsahookie; F. W. Abdalqahar
Abstract
Via mitochondrial genes, eukaryotes: such as plants, animals, human and yeast have evolved ways of cellular suicide that are known as Programmed Cell Death (PCD). In multicellular organisms, the organized destruction of cells is important in development and immunity and for forming body and specific organ shapes, as well as for removing superfluous, unwanted, damaged or infected cells. Furthermore, disfunction of PCD could lead to various diseases in humans, including cancer and several degenerative diseases. Two characterized systems for the study of plant PCD are those of the Hypersensitive Response (HR), which is often observed during plant–microbe interactions, and the development of tracheary elements in the xylem of vascular plants. A simplified depiction of the sequence of cytological events that take place during these forms of plant PCD is contrasted with those of "apoptosis", the well studied form of animal PCD. The "clean" process of apoptosis effectively contains the contents of the dead cell for removal by other cells and avoids activating an inflammatory response in animals. In the case of HR-associated cell death and the terminal differentiation of tracheary elements, the contents of the dying cells are not engulfed by other cells. In addition, the "corpse" of the dead cell is held in place by the cell wall, and for mature tracheary elements, the cell wall is reinforced during the early phase of PCD and carries out the essential function of mechanical support and transport after autolysis. The final collapse of the vacuole immediately precedes nuclear DNA fragmentation, which occurs at late stages of the cell death process before the final autolysis of the cell. These "key" characteristics therefore distinguish plant PCD from that of classic apoptosis and indicate that specialized features and pathways have probably evolved to control and execute the death program in plant cells. Taxonomy of all forms of PCD based on inhibitors, activators, and identified biochemical pathways involved in each form of PCD, and that should offer new insight into cell death associated with various disease states, and ultimately introduce new therapeutic approaches in human and animals. In plants, and by controlling PCD mechanism, the system capacity constant could be increased, and ultimately, the economic yield.

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