What do you mean by Totipotent cells? Explain in detail?
According to Haberlandt (1902), a German botanist, every living plant cell is totipotent, i.e., each cell is capable of regenerating a whole plant. This concept is base on the fact that each cell of an organism begins its development from a fertilised egg, hence, it must contain the inherent capacity to form the whole organism. The development of a whole organism from a single cell (zygote) is the result of the integration of cell division and cellular differentiation.
The cells isolated from different tissues are normally non-dividing and inactive. In order to express totipotency, the differentiated and matured cells first undergo the process of differentiation called cytodifferentiation. Haberlandt reported culture of isolated palisade cells obtained from leaves in Knop’s salt solution enriched with sucrose. The cells remained alive for upto one month, increased in size, accumulated starch but failed to divide. This led to the development of techniques for cultivation of plant cells under defined conditions.
The first embryo culture in plant science was done by Hanning (1904), who cultured nearly matured embryos of certain crucifers and grew them to maturity. Haploid plants from pollen grains were first produced by Maheswari and Guha in 1964 by culturing anothers of Datura. In 1960, Cocking produced-large quantities of protoplasts which are naked cells from which cell wall has been removed by using cell wall degrading enzymes. It is now possible to regenerate whole plant from protoplast.
In 1972, Carlson and his associates produced the first somatic hybrid plant by fusing the protoplasts of Nicotiana glauca and N.langsdorfii. The first plant from a matured plant cell was regenerated by Braun in 1959. Development of somatic embryos was first reported in 1958-59 from carrot tissues by Reinert and Steward independently. Subsequently, Steward in 1963 and Halperin and Wetherell in 1964 demonstrated the production of thousands of somatic embryos from carrot cells in cultured medium.
During the last century, totipotency of living cells has been practised in a wide variety of plant tissues obtained from anther, endosperm, nucellus, embryo, root tip, leaf, flower buds. Except in few animal cells like Rana and Xenopus, where the nuclei of both, blastula as well as gastrula are totipotent when transplanted in eggs, this unique property of cells is restricted to plant kingdom only.