Sensitivity of Lavender to Proton, Electron, and Gamma Radiation

Abstract

While ion beams are widely used in plant breeding, little is known about the sensitivity of Lavandula angustifolia (lavender) to ionizing radiation. To compare the biological effects of different types of ionizing radiation on the germination and survival rates of lavender, we exposed lavender seeds to gamma rays, 3 MeV electron beams, and 1.89 MeV proton ion beams. We observed that the seed germination rate decreased with increasing dosages of all three types of ionizing radiation. The malformation rate of lavender seedlings exposed to electron beams and gamma rays increased with increasing radiation dosage. By contrast, the effect of the accelerated proton beams on the malformation rate was negatively correlated with the dosage used. The survival rate of lavender seedlings exposed to the three types of ionizing radiation decreased in a dose-dependent manner. In addition, the survival rate of seedlings irradiated with proton and electron beams decreased more slowly than did that of seedlings irradiated with gamma rays. The half-lethal dose of gamma rays, electron beams, and proton beams was determined to be 48.1 Gy, 134.3 Gy, and 277.8 Gy, respectively, and the most suitable proton-ion energy for lavender seeds in terms of penetration depth was determined to be 5 MeV. These findings provide valuable information for the breeding of lavender by radiation mutation.Additional key words: half-lethal dose, high oil content, mutation breeding of lavender, radiation sensitivity, survival rate nonlinearly related to the LET, with the peak value of the survival curves being 113 keVㆍμm -1 (Tanaka et al., 1997).Proton beams have long been used as low-LET ionizing radiation. The LET values for 9 GeV, 645 MeV, and 50 MeV protons are 0.23, 0.25, and 1.25 keVㆍμm -1 , respectively. These values are close to the LET values of electron beams or gamma rays (value of gamma rays 0.2 keVㆍμm -1 ); however, they are considerably lower than those of heavy-element ion beams. Further, previous studies indicated that low-energy protons (<10 MeV, >4.6 keVㆍμm -1 ) have higher relative biological effectiveness (Yang, 1999). Consequently, low-energy protons can be considered as promising mutagens in plant breeding.Ion beams induce DNA damage and genomic instability in cells by generating reactive oxidative species (Esault et al., 2010;Mughal et al., 2012), which in turn inhibit cell division and cell elongation (Vazquez-Tello, 1996) and suppress tissue regeneration and germination (Zhou et al., 2006;Wu and Yu, 2001). In the context of mutation by ion beams, it has been reported that exposure of roses, carnations, and wheat to ion beams can induce a wide variety of mutations in flower color and flower shape (Okamura et al., 2003;Wu and Yu, 2001). The mechanisms underlying the biological effects of low-energy ion beams on plants may involve a combination of energy deposition, mass deposition, and the exchange of mass and charge (Lin and Yu, 1996).Lavender is widely grown for its essential oils in Asia and Europe. However, the oil content of lave...