Direct transformation implies that the cells take up the foreign gene of interest without the help of a vector.
DGT transformation methods are species and genotype-independent in terms of DNA delivery, but their efficiency is influenced by the type of target cell, and their utility for the production of transgenic plants in most cases depends on the ease of regeneration from the targeted cells, as most methods operate on cells cultured in vitro.There are a range of DGT techniques all with their own advantages and disadvantages, some are described below.
Direct Gene Uptake by Protoplasts
Protoplasts are cells without rigid cellulose walls. It has been shown that plant protoplasts treated with polyethylene glycol, commonly used to induce protoplast fusion, will take up DNA from their surrounding medium. More importantly, this can then be stably integrated into the plant chromosomal DNA.
Microinjection
A delivery system that involves the direct injection of foreign DNA into plant cells using minute needles. Microinjection of DNA into the nuclei of isolate protoplasts could be an efficient means of gene transfer.
Electroporation
This is a technique using electrical fields to make protoplasts temporarily permeable to DNA, and offers an effective alternative to vectors.
In electroporation plant cell protoplasts are suspended in a small chamber with electrodes at opposite ends. The suspension medium contains the DNA or other material to be inserted into the cells. Pulses of high voltages are applied to the electrodes. The high voltage produces pores in the plasma membranes, allowing the DNA (or other material) to diffuse into the cells. The membranes reseal after a short period. If properly treated, the cells can then regenerate cell walls, divide to form callus, and finally regenerate new plants.
Liposome Mediated DNA Delivery
Liposomes are small artificial lipid vesicles prepared from phosphatidyl choline and stearylamine by a process known as reverse-phase evaporation. Nucleic acid entrapped in such liposomes renders them highly tolerant to attack by nucleases. Techniques for fusing these liposomes to plant cell protoplast have been evolved.
Microprojectile Gun method
To overcome the limitations of protoplast regeneration, high velocity microprojectiles are being used to deliver nucleic acids directly into intact plant cells or tissues. In this method DNA is coated on the surface of tungsten particles which are projected by means of a particle gun into intact cells or tissues. The particles can penetrate through several layers of cells and can transform cells within tissue/explants. Soybean, tobacco, and maize have been transformed by this method.