Sinopsis
One of the most important biological events in the life cycle of an organism is fertilization, which involves the fusion of two gametes of opposite sex or strain resulting in the formation of a zygote. From this singlecelled zygote originates the entire multicellular and multiorganed body of a higher organism; may it be a flowering plant or a human body. In a flowering plant, for example, structures as morphologically and functionally diverse as underground roots, green photosynthesizing leaves, and beautiful flowers all arise from the single-celled zygote through millions of mitoses. The latter process is a type of cell division characterized by identical products. Theoretically, therefore, all the cells in a plant body, whether residing in the flowers, conducting tissues or root tips, should have received the same genetic material as originally present in the zygote. All this would then suggest that there must be some other factor(s) superimposed on the genetic characteristics of cells which bring about this vast variation expressed by the genetically identical cells. The process involved in the manifestation of these variations is called differentiation. The morphological differentiation is actually preceded by certain cellular and subcellular changes. A pertinent question that arises at this stage is: whether the cellular changes underlying differentiation of various types of cells are permanent and, consequently, irreversible, or whether it is merely a social feature in which a cell undergoes an adaptive change to suit the functional need of the organism in general and the organ in particular. The fact that during the normal life cycle of a plant a cell which has differentiated into a palisade cell dies as a palisade cell and an epidermal cell does not revert to meristemic state may suggest that the events leading to differentiation are of a permanent nature. However, the classic experiments of Vochting on polarity in cuttings, carried out in 1878, suggest otherwise. He observed that all cells along the stem length are capable of forming roots as well as shoots, but their destiny is decided by their relative position in the cutting. The best way to answer this question and understand more about the inter-relationship between different cells of an organ and different organs of an organism would, however, be to remove them from the influence of their neighbouring cells and tissues and grow them in isolation on nutrient media. To put it in the words of the great German botanist Gottlieb Haberlandt (1854-1945), now aptly regarded as the father of plant tissue culture, 'To my knowledge, no systematically organized attempts to culture isolated vegetative cells from higher plants in simple nutrient solutions have been made. Yet the results of such culture experiments should give some interesting insight to the properties and potentialities which the cell as an elementary organism possesses. Moreover, it would provide information about the inter-relationships and complementary influences to which cells within a multicellular whole organism are exposed'. Haberlandt was the first person to culture isolated, fully differentiated cells as early as 1898 and the above lines are cited from the English translation of his classic paper presented in 1902 in which he described the results of his pioneering experiments (Krikorian and Berquam, 1969).
Content
- Introductory history
- Laboratory requirements and general techniques
- Tissue culture media
- Cell culture
- Cellular totipotency
- Somatic embryogenesis
- Haploid production
- Triploid production
- Variant selection
- In vitro pollination and fertilization
- Zygotic embryo culture
- Protoplast isolation and culture
- Somatic hybridization and cybridization
- Genetic engineering
- Production of pathogen-free plants
- Clonal propagation
- Production of secondary metabolites
- Germplasm storage
