Although plants are more difficult to work with than bacteria, gene insertions can be made into single plant cells. Then the cells can be cultivated to form a mature plant. The major method for inserting genes is through the plasmids of the bacterium called Agrobacterium tumefaciens. This bacterium invades plant cells, and its plasmids insert into plant chromosomes carrying the genes for tumor induction. Scientists remove the tumor‐inducing genes and obtain a plasmid that unites with the plant cell without causing any harm.
Recombinant DNA and biotechnology have been used to increase the efficiency of plant growth by increasing the efficiency of the plant's ability to fix nitrogen. Scientists have obtained the genes for nitrogen fixation from bacteria and have incorporated those genes into plant cells. The plant cells can then perform a process that normally takes place only in bacteria.
DNA technology has also been used to increase plant resistance to disease by reengineering the plant to produce viral proteins. Also, the genes for an insecticide obtained from a bacterium have been inserted into plants to allow the plants to resist caterpillars and other pests.
One of the first agricultural products of biotechnology was the rot-resistant tomato. This plant was altered by adding a gene that produces an antisense molecule. The antisense molecule inhibits the tomato from producing the enzyme that encourages rotting. Without this enzyme, the tomato can ripen longer on the vine.