# Biological Effect of Gamma Rays According to Exposure Time on Germination and Plant Growth in Wheat
## 3 Results  
### Free Radical Contents and Plant Growth  
To examine the oxidative stress produced by gamma irradiation, we measured the free radical contents in irradiated and control seeds. The mean differences in the free radical levels were significant according to the gamma radiation dose and time (Figure 1). The free radical content increased dose-dependently in the case of both long- and short-term gamma irradiation. Interestingly, we observed that the free radical content was significantly higher in the long-term irradiated seeds compared to their short-term irradiated counterparts. The relative free radical levels significantly increased in the case of all long-term gamma irradiation treatments, showing a more than 5-fold increase compared with the control levels. In the case of the short-term treatment, the free radical content increased slightly (1.1-1.5-fold) compared with the control levels.  
Figure 2 shows the daily wheat seed germination percentage. The germination percentages in DAG1 and DAG2 showed a significant difference between the short-term irradiation, including the control, and the long-term irradiation with gamma rays. The final germination percentage did not show a significant difference between the control and the irradiated seeds. Data analysis revealed that the GRI and MGT were affected by the gamma-ray dose and exposure time (Table 1). The GRI showed a tendency to decrease with prolonged exposure at the same dose of gamma radiation. The MGT was slower in the case of long-term irradiation. The MGT increased with an increase in the gamma-ray dose and exposure time. The shoot and root lengths decreased dose-dependently (Figure 3). The growth of plants treated with short-term gamma irradiation exposure was slightly reduced compared with the non-irradiated samples, whereas exposure to long-term irradiation caused severe growth inhibition. In the case of long-term irradiation, the shoot and root lengths decreased drastically as the radiation doses increased. These results indicate that the free radical content increase according to the radiation dose and exposure time increase is closely related to plant growth. Moreover, our results indicate that the high free radical levels affected the early stage of wheat development by reducing the ability of the seeds to germinate or delaying their development. The RD\({}_{50}\) values determined by plant growth  
characteristics were 158.6 Gy and 206.3 Gy (shoot and root length in the case of short-term irradiation, respectively) and 202.8 Gy and 252.5 Gy (shoot and root length in the case of long-term irradiation, respectively) (Supplementary Figure S1).  
Figure 1: Measurements of the free radical content in wheat seeds following short- and long-term gamma irradiation using electron spin resonance (ESR). Con, non-irradiated seeds (0 Gy); S, short-term irradiation; L, long-term irradiation; 100, 300, and 500, gamma irradiation doses. Each bar represents the mean \(\pm\) standard deviation (SD). Values with different letters are significantly different using [PERSON]’s multiple range test (\(p<0.05\)).  
Figure 2: Gamma radiation dose and exposure time effects on seed germination percentage. The seed germination percentages were determined daily for 4 days. DAG, days after germination. Each bar represents the mean \(\pm\) SD.