Figure 1.
Scheme of Mutation Inductions by gamma radiation for the genetic improvement of plants. (A) Gamma radiation (GR) is one of the most widely used mutagenic agents in plants, because it is reported to induce high genetic variability. This type of radiation can be generated by radioisotopes such as carbon-14 (14C), cobalt-60 (60Co), cesium-137 (137Cs), and plutonium-239 (239Pu) [1]. Gamma rays (B) interact indirectly through (C) Radiolysis of water produces (D) reactive oxygen species (ROS) (hydrogen peroxide (H2O2), superoxide anion (O2), hydroxyl radical (OH), and singlet oxygen (O=O)) that generate lipid peroxidation and alter the structure of DNA and proteins [2,3,4]. (E) By increasing the ROS concentration, oxidative stress triggers the defense of the plant, which is modulated by enzymes such as peroxidase, ascorbate peroxidase, superoxide dismutase, and glutathione reductase [2,6]. Primary gamma radiation lesions delay or inhibit cell division and affect mitotic activity, growth rate or habit, dilation of thylakoid membranes, photosynthesis, modulation of the antioxidant system, and accumulation of phenolic compounds [7]. (F) Direct gamma radiation can generate base modifications and (G) single or double DNA strand breaks [8]. A twofold mechanism is involved in the natural repair of these errors: (H) Homologous Recombination (HR), an error-free repair mechanism; and (I) Non-Homologous End-Joining (NHEJ), a mechanism with a greater probability of generating mutations in the repair site, including deletions, insertions, and substitutions, among others [9].