The convention breeding methods are the most widely used for crop improvement. But in certain situations, these methods have to be supplemented with plant tissues culture techniques either to increase their efficiency to be able to achieve the objective, which is not possible through the conventional methods. One example of such situation would illustrate the point. The production of purelines or inbreeds involves six to seven generations of selfing. Production of haploids through distance crosses or using pollen, anther or ovary culture, followed by chromosome doubling, reduces this time to two generations. This represents a saving of four to six years. The other example is the transfer of a useful bacterial gene say, cry (crystal protein) gene from Bacillus thuringiensis, into a plant cell and ultimately, regeneration of whole plants containing and expressing this gene (transgenic plants). This can be achieved only by the combination of tissue culture and engineering; none of the conventional breeding approaches can ever produce such a plant.
The term tissue culture is commonly used in a very wide sense to include in vitro culture of plant cells, tissues as well as organs. But in a strict sense, tissue culture denotes the in vitro cultivation of plant cells in an undifferentiated mass e.g., callus cultures. Another term cell culture is use for in vitro culture of single or relatively small groups of plant cells, e.g., suspension cultures. But in general, the term tissue culture is applied to both callus and suspension cultures and the cell culture are often used for callus culture as well. When organized structures like root tips, shoot tips, embryos, etc. are cultured in vitro to obtain their development as organized structures, it is called organ culture. The plant tissue is used in its broad sense to denote aseptic in vitro culture of plant cells, tissues and organs.
The in vitro techniques were developed initially to demonstrate the totipotency of plant cells predicted by Haberlandt in 1902. The ability of single plant cell to develop into a whole plant. In 1902, Haberlandt reported culture of isolated single palisade cell from leaves in knop’s salt solution enriched with sucrose. The cells remained alive for up to one month, increased in size, accumulated starch, but failed to divide. Efforts to demonstrate totipotency led to the development of techniques for cultivation to plant cells under defined conditions. This was made possible by the brilliant contributions from R.J Gautheret in France and P.R White in U.S.A. during third and fourth decades of 20th century. Most of modern tissue culture media have been derived from the work of Skoog and co-workers during 1950 and 1960.
The first embryo culture was carried out by Hanning in 1904; he cultured nearly mature embryos of certain Crucifers an d grew them to maturity. The technique was utilized by Laibach, in 1925, to recover hybrid progeny from an inter-specific cross in Linum. Subsequently, contributions from several workers have led to the considerable refinements in this technique.
Haploid plants from pollen grains were first produced by Maheshwary and Guha in 1964 by anthers culturing of Datura. This marked in the beginning of anther culture and pollen culture for the production of haploid plants. The technique has been further developed by many workers, more notably by J.P Nitch and co-workers. These workers showed that isolated microspores of tobacco produce complete plants.
Plant protoplasts are naked cells from which cell wall have been removed. In 1960, Cocking produced large quantities of protoplasts by using cell wall degrading enzymes. The techniques of protoplast production have now been considerably refined. It is now possible to regenerate whole plants from protoplasts and also to fuse protoplasts of different plant species. In1972 Varlson and co-workers produced first somatic hybrid plant by fusing the protoplasts of Nicotiana glauca and Nicotiana langsdorfii.
A successful establishment of callus cultures depended on the discovery during mid-thirties of IAA (indol-3-acetic acid), the endogenous Auxin, and the role of Vitamin B complex in plant growth and in root cultures. The first continuously growing callus cultures were established from cambium tissue in 1939 independently by Gautheret, White and Nobecoat. The subsequent discovery of kinetin by Miller and coworkers in 1955 enabled the initiation of callus cultures from differentiated tissues. Shoot bud differentiation from tobacco pith tissues cultured in vitro was reported by Skoog in 1944, and in 1957 Skoog and Miller proposed that root-shoot differentiation in this system was regulated by auxin-cytokinin ratio. The first plant from a mature cell was regenerated by Braun in 1959. The development of somatic embryos was first reported in 1958-1959 from carrot tissue by Reinert and Steward independently.
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