电子束辐射对大麦种胚核酸合成活性的损伤效应

Lowering of Barley Embryo Nucleic Acid Synthesis Activity Induced by Electron Beam Irradiation

电子束辐射损伤大麦种胚核酸合成能力的效应主要表现在使DNA复制合成启动推迟 ,使DNA复制、RNA合成活性下降。吸涨过程中大麦种胚的DNA复制合成有一明显的启动过程 ,RNA合成则无明显的启动过程。 2 0 0与 40 0Gy电子束辐射分别使DNA复制合成启动推迟约 2与 4h ;电子束辐射对DNA复制合成活性的抑制作用强于对RNA合成活性的抑制。在 5 0～ 5 0 0Gy范围内 ,大麦种胚DNA复制、RNA合成活性均随辐射剂量呈指数下降 ,其半对数斜率分别为- 0 .0 0 39与 - 0 .0 0 14。根据实验计算 ,电子束辐射对DNA复制合成的LD50 、D37分别为 178与 2 5

The damage of embryo nucleic acid synthesis activity induced by electron beam irradiation (EB irradiation) on intact dry seeds of barley ( Hordeum vulgare L., cv. Zhe Nong Da No.3 ) was studied by measuring the DNA and RNA synthesis activities as the degree of incorporation of 3H thymidine or 3H uridine into the barley embryos. With dry seeds, flow cytometric profiles indicated that the majority of the cells were arrested at the G 1 phase of the cell cycle. A lag phase was observed during embryo cell DNA replication, and a sharp turnover of DNA synthesis occurred 10～12 h after imbibition of water, while cells at G 1 phase were observed to develop into S phase by flow cytometric analysis of nuclear DNA analysis. The onset of DNA replication was [HJ6:2]delayed 2 h or 4 h by 200 Gy or 400 Gy EB irradiation respectively. The rate of DNA replication, RNA synthesis in barley embryos labeled with 3H thymidine or 3H uridine for 2 h after imbibing for 16 h decreased exponentially with increasing dosage of EB irradiation up to 500 Gy. The lowering effect of EB irradiation on DNA replication activity was much stronger than that on RNA synthesis, with the slopes of their semilogarithmic curves being -0.0039 and -0.0014 respectively. According to this experiment,the 50% inhibitory dosage and lethal dosage of electron beam for DNA synthesis activity in barley embryos were about 178 and 256 Gy respectively.