BIOTECHNOLOGY - Inshyna N.M. - 2009

CHAPTER 3. CELL ENGINEERING

Cellular Selection

Cells in in vitro culture vary in Morphology, biochemical properties, physiological state, and genetics. This phenomenon is known as somaclonal variation. The genetic nature and mechanisms underlying somaclonal variation remain insufficiently studied. The heterogeneity of Cell cultures stems from both genetic and modificational Variability. Mutations occur at the Gene, chromosomal, and genomic levels. Cells with varying levels of ploidy differ in division and growth rates; eventually, one cell type becomes dominant, and cellular Selection takes place. Modificational changes in cultured cells are adaptive in nature, ensuring physiological acclimatization. The spontaneous emergence of various variant cell lines in culture can be harnessed to improve existing crop varieties. Of particular practical importance is the creation of plant forms resistant to adverse environmental factors, such as low temperatures, soil salinity, environmental pollution by toxic substances, and pest infestations. The application of cellular technologies significantly accelerates the breeding process.

To accelerate selection in cell cultures, chemical and Physical Mutagens are employed. To increase mutation frequencies in somatic cells, researchers most frequently use mutagens such as nitrosoguanidine, nitrosomethylurea, and methyl methanesulfonate. Irradiation with ultraviolet light, γ-quanta, ⁶⁰Co, and neutrons is utilized less frequently. Selective agents include Antibiotics, nucleic acid synthesis inhibitors, purine and pyrimidine base analogues, phytotoxins, amino acid analogues, and agents inducing Water and salt stress.

Objects used for in vitro cellular selection include callus cultures and isolated protoplasts, somatic or androgenic embryo cultures, isolated embryo cultures, organoids, or explants (leaf and stem segments).

Advantages of the in vitro cellular selection method compared to whole-plant selection:

- mutant traits manifest quite rapidly at the single-cell level;

- novel Types of mutations, including those of a biochemical nature, can be obtained;

- space efficiency: a Petri dish 10 cm in diameter can accommodate the cultivation of 10⁷—10⁸ cells, whereas an equivalent number of plants would require over 1,000 hectares of land;

- significant savings in time and labor when acquiring a desired trait.

Conducting selection at THE CELLULAR LEVEL makes it possible to generate new

plant forms 2 to 4 times faster than through traditional breeding Methods. For instance, developing new varieties using cellular selection takes an average of 3 to 4 years, whereas whole-plant selection requires 10 to 12 years. The primary prerequisite for the successful Structure/175.html">Implementation of cellular selection is an efficient Plant Regeneration system.