Mutagenesis—A Potential Approach for Crop Improvement - Crop Improvement: New Approaches and Modern Techniques - page 157

Fig. 4.2 The schematic view of E5B beam line. (RRC = RIKEN Ring Cyclotron)
perature during treatment. The concentration of chemical mutagen is determined
by the per cent strength of the chemical in the solvent (distilled water). The volume
of treatment solution is also equally important so as to provide each seed or organ
an opportunity to absorb the same number of moles of mutagen. It is generally ac-
cepted that a treatment giving 30-40 % growth reduction is likely to give an optimal
mutation yield in crops. The treatment duration must provide an opportunity for
hydration and full penetration through the treated tissue of the mutagen. Long treat-
ment is advisable, but it can be shortened by using pre-soaked seeds. However, the
treatment duration also depends on the hydrolytic rate of the mutagen. For a short
period, a high concentration is used after pre-soaking at high temperatures. The
temperature of mutagenic solution greatly influences the mutagenic process. When
there is no published information of mutation dose in a particular crop, we often re-
sort to LD 50 (Lethal Dose-50), which is a common parameter to decide the effective
doses of both physical and chemical mutagens (Albokari et al. 2012 ). Thus, LD 50 is
a dose, which results in 50 % mortality of treated seeds (Roychowdhury 2011 ). With
ionizing radiations, a dose which restricts survival to 50 % (LD 50 ) or growth to 50 %
(GR 50 ) is a good treatment.
IonBeamMutagenesis
Application of ion beams for mutation induction was started with low-energy
ions in China in the late 1980s and with heavy ions in Japan in the early 1990s.
While ion beam technology has been used for food crop improvement in China,
it has been more extensively used for floriculture plants in Japan. Ion beams as
a mutagen are different from other physical mutagens such as gamma or X-rays
in that they not only involve energy transfer (as gamma or X-rays), but also mass
deposition and charge exchange (Hase et al. 2012 ); hence could result in complex
DNA damage and changes that are not found when gamma or X-rays are used
(high percentage of double strand breaks and subsequent chromosome aberrations).
Ion beams are produced by particle accelerators, i.e. cyclotrons. Figure 4.2 is a
schematic view of the E5B beam line available in the RIKEN Accelerator Research
Facility (RARF), Japan.