49. Radiation Effects on Growth and Seed Germination of Arabidopsis

Yoshito Watanabe, Masae Yukawa, Kim Hee-Sun and Yoshikazu Nishimura

Keywords: environmental protection, plants, arabidopsis, germtnatton

With the increasing interest about the impact of human activities on the ecology, envuronmental protection against ionizing radiation is getting attention. There is, however, only limited information about radiation effects on environmental organisms such as plants. In field studies of a nuclear accident, deleterious effects such as poor growth and genetic damages were observed in plants after a large dose of irradiation. On the other hand, some reports have shown that a low dose of irradiation could stimulate plant growth. In this study, we used a biological model plant, arabidopsis, to elucidate the radiation effects on plants.

The seeds of arabidopsis (var. Columbia) were surface sterilized and soaked in water at 4C for 2 days, before being cultured on the medium containing 0.8% agar under light in a controlled environment chamber. The plants were irradiated with X rays (0.5 20 Gy, l Gy/min) or gamma rays (50 Gy 1000 Gy, 10 Gy/min) at various growth stages. When young plant seedlings were irradiated, their root elongation was inhibited at doses more than 100 Gy, although elongation of the hypocotyls was not affected even at 1000 Gy. This indicates that the inhibition of growth by a high dose of irradiation var ies with tissues, and the root is relatively sensitive to irradiation.

Irradiation of seeds did not affect their germination when they were cultured at the cultural fern perature of 23C. However, when the seeds were cultured at 8C which is almost the lower limit for germination, the irradiated seeds germinated faster than the non-irradiated seeds. The effect of seed irradiation could be observed at a dose as low as 0.5 Gy. The acceleration of germination by seed irradiation was observed not only under the chilling stress, but also under the stress induced by a chemical agent. When seeds were grown at 23C on medium containing methyl viologen, a biological radical generator, pre-irradiation of seeds reduced the methyl viologen-induced retardation of germination (Fig 16) . This suggests that irradiation of seeds could enhance anti-oxidant systems that enable seeds to germinate promptly under stress.

Fig.16. Reducation of methyl viologen (MV) -induced retardation of seed germination by X-ray pretreatment.