Plant Propagation and Nursery Management (1+1)

Principles and Practices

A. Totipotency and plant regeneration: The term totipotency was coined by Germen plant physiologist Haberlant in 1902. This is achieved by excising the explants and placing it on culture medium, which involves the following consecutive events:

1) Differentiation of source tissue or organ, as a result of which, all physiological mechanism activate in the cell, which leads to cell division.
2) Active cell division in the entire cut surface of the explants, resulting in proliferation of the callus tissue.
3) Organization of defined meristems, resulting in formation of shoot or root meristems or both.
4) Regeneration and differentiation of new organs through organogenesis or somatic embryogenesis.

B. Axillary bud proliferation

• It is considered a convenient route for micropropagation, because it does not include a callus stage and is considered safe for the preservation of clonal characteristics.
• It has been observed by many workers that a large number of axillary shoot buds grow extensively when shoot-tips or even smaller apical meristems are cultured in an appropriate culture medium, containing higher concentration of cytokinin.
• Both the excision of the explants and the cytokinin rich medium activate the bud, leading to proliferation of many side shoots, which can later be separated for further culture.
C. Organogenesis (Development of organs)

• Organogenesis from explants results in the formation of both shoots and roots.
• Generally shoots are formed first than roots.
• The regeneration of other organs occur later on, either in the same media or after sub-culturing in another medium, supplemented with different concentration of salt under different environmental conditions.
D. Somatic embryogenesis

• Somatic embryogenesis is different from organogenesis in that the regeneration and organization are bipolar i.e. the shoots and root meristems in the explants are formed simultaneously from pre-embryonic masses.
• Differentiation and organization of somatic embryogenesis usually, a two stage culture is involved.
• First induction of pre-embryonic masses, which is usually favoured by 2,4-D or other auxins and second, by the transfer of the pre-embryonic masses to a differentiation medium in which the somatic embryos fully differentiate into organs.