The main objective in plant cultures is to regenerate a plant or plant organ from the callus culture. The regeneration of plant or plant organs only taken place by the expression of cellular totipotancy of the callus tissues. Scattered areas of actively dividing cells, known as meristematic centres, develop as a result of differentiation and their further activity results in the production of root and shoot primordia. These processes can be controlled by adjusting the cytokinins: auxin ratio in culture medium. The production of adventitious roots and shoots from cells of tissue is called organogenesis.
Definition of Organogenesis:
“The development of adventitious organs or primordia from undifferentiated cell mass in tissue culture by the process of differentiation is called organogenesis.
“The formation of roots, shoots or flower buds from the cells in culture in manner similar to adventitious root or shoot formation in cuttings is called organogenesis.
Type of organogenesis by which only adventitious shoot bud initiation take place in the callus tissue.
Type of organogenesis by which only adventitious root formation takes place in the callus tissues.
In some culture tissues, an error occurs in development programming for organogenesis and an anomalous structure is formed. Such anomalous organs like structures are known as Organoids. Although Organoids contain the dermal, vascular and ground tissues present in plant organs, they differ from true organ in that the Organoids are formed directly from the periphery of the callus tissue and not from organised mersitemoids.
Meristemoid is localized group of meristematic cells that arise in callus tissue and may give rise to shoots and or roots. They are also termed as nodules or growth centres.
In plant tissue culture, during growth and maturation of callus tissue or free cells in suspension culture, few dedifferentiated cells undergo cytoquiescece and cytosenescence and this twin phenomenon are mainly associated with redifferentaition of vascular tissues, particularly tracheary elements. The whole developmental process is termed as cytodifferetiation.