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Organogenesis and Embryogenesis -

Organogenesis refers to the induction of morphologically well defined organs such as the shoot or root from callus cultures. Skoog and Miller (1957) pointed out that a balance between the relative levels of auxin and cytokinin played a great role in the initiation of shoot and root.

Embryogenesis refers to the development of somatic bipolar adventive embryoids from callus cultures under certain nutritional and hormonal conditions.

This development follows a sequence through proembryoid, globular, and torpedo stages.

The technique of cloning isolated single cells in vitro has demonstrated the fact that somatic cells, under appropriate conditions, can differentiate to a whole plant. This potential of the cell to grow and develop a multicellular or multiorganed higher organism is termed cellular totipotency.

Since the potential lies mainly in cellular differentiation, this indicates that all genes responsible for differentiation are present within individual cells and many of them that remain inactive in differentiated tissues or organs are able to express only under adequate culture conditions.

Development of an adult organism from a single cell or zygote is the result of the integration of cell division and cell differentiation. Isolated cells from differentiated tissues are generally non dividing and quiescent; to express totipotency the differentiated cell first undergoes dedifferentiation and then redifferentiation.

The phenomenon of a mature cell reverting to a meristematic state and forming undifferentiated callus tissue is termed dedifferentiation, whereas the ability of a dedifferentiated cell to form a whole plant or plant organs is termed redifferentiation.

 
 

 
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