ABSTRACT
Since the observation of mutation induction with x-rays in Drosophila by Muller (1927) and with x-rays and gamma rays in maize and barley by Stadler (1928), a number of plant mutations have been induced by ionizing radiation and used for plant science and breeding. The biological effects of ion beams have also been investigated and it has been found that ion beams show a high relative biological effectiveness (RBE) in lethality, mutation, and so on compared to low linear energy transfer (LET) radiation such as gamma rays, x-rays, and electrons (Blakely, 1992). As ion beams deposit high energy on a local target, it is suggested that ion beams predominantly induce single-or doublestrand DNA breaks with damaged end groups whose reparability would be low (Goodhead, 1995)
33.1 Introduction .......................................................................................................................... 943 33.2Ion-Beam Irradiation ............................................................................................................944 33.3Biological Effects of Ion Beams ...........................................................................................946 33.4Mutation Induction ............................................................................................................... 947
33.4.1Determination of Irradiation Dose ........................................................................... 947 33.4.2 Mutation Frequency .................................................................................................. 947 33.4.3Determination of Population Size for Mutation Induction .......................................948 33.4.4Mutation Spectrum ................................................................................................... 949 33.4.5Molecular Nature of Mutation Induced by Ion Beams ............................................. 950
33.5Novel Mutants Induced by Ion Beams .................................................................................. 950 33.5.1 Model Plants ............................................................................................................. 950 33.5.2Crops ......................................................................................................................... 952 33.5.3Ornamental Flowers ................................................................................................. 952 33.5.4Trees .......................................................................................................................... 952
33.6Other Biological Effects of Ion Beams ................................................................................. 953 33.6.1 Cross Incompatibility ............................................................................................... 953 33.6.2Sex ModiŸcation ....................................................................................................... 953 33.6.3Activation of Endogenous Transposable Element .................................................... 953
33.7Conclusion and Perspective .................................................................................................. 953 Acknowledgments .......................................................................................................................... 955 References ...................................................................................................................................... 955
(Figure 33.1). Therefore, it seems plausible that ion beams can frequently produce large DNA alterations such as inversions, translocations, and deletions rather than point mutations, producing characteristic mutants induced by ion beams. However, the characteristics of ion beams for mutation induction have not been elucidated yet. On the other hand, more than 2200 mutant varieties of cereals, beans, ¡owers, etc., have been ofŸcially registered to FAO/IAEA organization (FAO/IAEA, 2006), most of which are induced by ionizing radiations, chie¡y gamma rays. As saturations for gamma-or x-ray mutanization have been realized in several kinds of mutant phenotypes because of its long history of about 80 years, new chemical or physical mutagens were expected to come into existence.
