Effect And Mechanism Of Carbon Heavy Ion Beam Irradiation On Wheat Disease Resistance

Recent years, more and more peoples pay enough attentions to the biological effects induced by heavy ion beam in the medicine and biology domain. In terms of the previous study on crops heredity improvement, we know that heavy ion beam as a new mutation source which had potential advantages, is one of an important ways to supplement conventional breeding.Taken advantage of the unique characters of heavy ion beam, enhancement of crop disease resistance and cultivation of excellent disease-resistant varieties will bring the profound influence in agricultural production. Hence, it is indispensable to investigate the mechanism of plant disease resistance on heavy ion beam. Consequently, these data provide the more information to support irradiation mutagenic breeding in the further.The present study was designed to evaluate the effects of heavy ion beam on the changes and mechanisms of leaf rust resistance in wheat seedlings when the dry seeds of wheat were irradiated with heavy ion beam. From the macroscopic biology and molecular biology view, the main discussion is aimed to explore the response relationship between the changes of along with cell wall reactive oxygen species (ROS) caused by heavy ion beam and the variation of plant disease resistance. In the study, wheat seeds exposed to ¹²C⁶⁺ ion beam with different doses (10～80Gy). After germination of 10 day, we examined disease-resistant index, the quantification of plant survival and growth, and cell wall contents and uronic acid contents as well as ROS-related biomarkers in wheat seedlings. The results are as follows:First, the data showed that irradiation-treated groups equally decreased disease index, and especially significant change were observed in 20Gy for irradiation. It was suggested that heavy ions obviously augment plant disease resistance. Secondly, the observation of the quantification of plant survival and growth showed that low dosages of irradiation (10Gy-20Gy) stimulated the increase of wheat survival and growth as compared to control group (0Gy). In contrast, higher dosages (40Gy-80Gy) for irradiation inhibited wheat survival and growth. Thirdly, through measuring uronic acid contents of cell wall, we found that heavy ion increased uronic acid contents, indicated that cell wall components have been changes induced by heavy ion.Another important disclose is heavy ion enhanced ROS reflected by the production of O2-, H2O2 and NO as well as TBARS contents, and 20Gy for irradiation achieved the peak value. The data demonstrated that the potential mutagenic mechanism of low dosages of irradiation may be closely associated with ROS yield, while the mutagenic mechanism for high dosages is possibly related to direct DNA damage. Simultaneously, increase of SOD activity was induced by heavy ions to counteract ROS accumulation.Together with above results, we conclude that the mechanisms of leaf rust resistance in wheat seedlings is due to three aspects: 1) Heavy ion promotes the speed of growth and shortens the cycle of growth, and in turn reduces leaf disease. 2) Heavy ion varies the structure and contents of cell wall, and consequently strengths stability of cell wall to avoid invasion of pathogenic microorganism. 3) Accumulated ROS(H₂O₂,O₂^-, NO) induced by heavy ion can directly kill pathogenic microorganism, and also indirectly improve plant disease resistance as signaling molecules. On the other hand, the above observations imply that an optimal dose is likely approximately 20Gy which may promise for wheat mutation breeding.