Tomato line 8338 was developed by introducing into the genome of a processing tomato cultivar UC82B a gene for 1-amino-cyclopropane-1-carboxylic acid deaminase (ACCd) derived from a nonpathogenic soil bacterium (Pseudomonas chlororaphis). In the plant, this enzyme catalyzes metabolism of 1-amino-cyclopropane-1-arboxylic acid (ACC), an essential precursor for the biosynthesis of the plant ripening hormone ethylene.

The initiation and progression of tomato fruit ripening depends on increased levels of ethylene. In line 8338, ACC is sufficiently reduced in detached fruit so that ethylene becomes limiting and the ripening process is delayed. Line 8338 has also been transformed with the nptII gene derived from Escherichia coli that encodes the enzyme NPTII. NPTII confers resistance to certain antibiotics, such as kanamycin, that are used to select transformed cells.