Another source of plant material for transformation is tissue culture, where cells are growing under aseptic conditions. The following steps are all carried out under sterile tissue culture conditions, with the plant tissue growing on an artificial agar medium. The explant is subjected to the transformation procedure. The goal is to transform as many cells as possible in the tissue. Even though all of the cells that are transformed may have received the same piece of DNA, the site at which the DNA integrates into the chromosome is different in each cell and this means that every transformed cell is genetically different.
Selection is applied to identify the rare cells that have been transformed.
Only transformed cells will be able to grow under these selection conditions. Without this selection, many more plants would have to be regenerated and then screened later to find the rare transformed plant. The composition of the growth medium, especially the levels of auxin and cytokinin hormones, are altered so that differentiated plants will regenerate from transformed cells. Overhead of general approach to plant transformation. Notice that this scheme is very similar to that used with bacteria through the first three steps, until you have to regenerate a multicellular organism.