Agrobacterium tumefaciens, a plant pathogen, is commonly used as a vector for the introduction of foreign genes into plants and consequent regeneration of transgenic plants. A. tumefaciens naturally infects the wound sites in dicotyledonous plants and induces diseases known as crown gall. The bacterium has a large plasmid that induces tumor induction, and for this reason, it was named tumor-inducing (Ti) plasmid. The expression of T-DNA genes of Ti-plasmid in plant cells causes the formation of tumors at the infection site. The molecular basis of Agrobacterium-mediated transformation is the stable integration of a DNA sequence (T-DNA) from Ti (tumor-inducing) plasmid of A. tumefaciens into the plant genome. A. tumefaciens-mediated transformation has some advantages compared with direct gene transfer methods such as integration of low copy number of T-DNA into plant genome, stable gene expression, and transformation of large size DNA segments. That is why manipulations of the plant, bacteria and physical conditions have been applied to increase the virulence of bacteria and to increase the transformation efficiency. Preculturing explants before inoculation, modification of temperature and medium pH, addition chemicals to inoculation medium such as acetosyringone, changing bacterial density, and co-cultivation period, and vacuum infiltration have been reported to increase transformation. In this chapter, four new transformation protocols that can be used to increase the transformation efficiency via A. tumefaciens in most plant species are described.
Part of the book: Genetic Engineering
Dormancy is when there is a lack of germination in seeds or tubers even though the required conditions (temperature, humidity, oxygen, and light) are provided. Dormancy is based on hard seed coat impermeability or the lack of supply and activity of enzymes (internal dormancy) necessary for germination. Dormancy is an important factor limiting production in many field crops. Several physical and chemical pretreatments are applied to the organic material (seeds/tubers) to overcome dormancy. Physical and physiological dormancy can be found together in some plants, and this makes it difficult to provide high-frequency, healthy seedling growth, since the formation of healthy seedlings from the organic material (seeds/tubers) sown is a prerequisite for plant production. This chapter will focus on the description of four different methods we have not seen reported elsewhere for overcoming dormancy.
Part of the book: Seed Biology