Physiologic and molecular responses of indica–japonica subspecies tetraploid rice seed germination to ion beams

Ionizing radiation can not only reduce the yield of rice but also cause rice toxicity, and consumption of this kind of rice threatens human health. Moreover, the production and application of freon has further caused a hole in the earth’s ozone layer, increasing the amount of ionizing radiation from the sun affecting rice. To select and breed new radiation-resistant rice varieties, dry seeds of the indica–japonica subspecies of tetraploid rice subjected to different doses of ionizing radiation were investigated for their responses during germination. The results showed that the relative water absorption, seed vigour and GA(3) content sharply decreased in response to three different doses of ionizing radiation, and the regulation of the expression of genes related to α-amylase synthesis and gibberellin metabolism was disrupted. Moreover, the degree of inhibition increased with increasing dose. Notably, under 3.0 × 10(17) ions/cm(2) radiation, an upregulation of OsGA3ox2 expression resulted in a sharp increase in GA(3) content in the indica–japonica tetraploid rice, and upregulated expression of OsAmy3A and OsAmy3D resulted in sharp increase in α-amylase activity, water absorption, and sucrose and fructose contents, which resulted in the seed vigour being greater than that of its parents. The results indicate that additional research on the physiological and molecular features of indica–japonica tetraploid rice seed germination in response to ionizing radiation is needed.