Yang Gen, Mei Tao, Yuan Hang, Zhang Weiming, Chen Lianyun, Xue Jianming, Wu Lijun, Wang Yugang
State Key Laboratory of Nuclear Physics and Technology, Peking University, Beijing 100871, People's Republic of China.
Radiat Res. 2008 Sep;170(3):372-80. doi: 10.1667/RR1324.1.
To date, radiation-induced bystander effects have been observed largely in in vitro single-cell systems; verification of both the effects and the mechanisms in multicellular systems in vivo is important. Previously we showed that bystander/ abscopal effects can be induced by irradiating the shoot apical meristem cells in Arabidopsis embryos. In this study, we investigated the in vivo effects induced by 30 keV 40Ar ions in intact Arabidopsis seeds and traced the postembryonic development of both irradiated and nonirradiated shoot apical meristem and root apical meristem cells. Since the range of 30 keV 40Ar ions in water is about 0.07 microm, which is less than the distance from the testa to shoot apical meristem and root apical meristem in Arabidopsis seeds (about 100 microm), the incident low-energy heavy ions generally stop in the proximal surface. Our results showed that, after the 30 keV 40Ar-ion irradiation of shielded and nonshielded Arabidopsis seeds at a fluence of 1.5 x 10(17) ions/cm2, short- and long-term postembryonic development, including germination, root hair differentiation, primary root elongation, lateral root initiation and survival, was significantly inhibited. Since shoot apical meristem and root apical meristem cells were not damaged directly by radiation, the results suggested that a damage signal(s) is transferred from the irradiated cells to shoot apical meristem and root apical meristem cells and causes the ultimate developmental alterations, indicating that long-distance bystander/ abscopal effects exist in the intact seed. A further study of mechanisms showed that the effects are associated with either enhanced generation of reactive oxygen species (ROS) or decreased auxin-dependent transcription in postembryonic development. Treatment with the ROS scavenger dimethyl sulfoxide (DMSO) or synthetic auxin 2,4-dichlorophenoxyacetic acid (2,4-D) can significantly reverse both the alterations in postembryonic development and auxin-dependent transcription, suggesting that ROS and auxin-dependent transcription processes play essential roles in the low-energy heavy-ion radiation-induced long-distance bystander/abscopal effects in the intact organism.
迄今为止，辐射诱导的旁观者效应主要是在体外单细胞系统中观察到的；在体内多细胞系统中验证这些效应及其机制很重要。此前我们表明，通过照射拟南芥胚胎中的茎尖分生组织细胞可以诱导旁观者/远隔效应。在本研究中，我们研究了30 keV 40Ar离子对完整拟南芥种子诱导的体内效应，并追踪了受辐照和未受辐照的茎尖分生组织和根尖分生组织细胞的胚后发育。由于30 keV 40Ar离子在水中的射程约为0.07微米，小于拟南芥种子中从种皮到茎尖分生组织和根尖分生组织的距离（约100微米），入射的低能重离子通常会在近端表面停止。我们的结果表明，在以1.5×10(17)离子/cm2的注量对屏蔽和未屏蔽的拟南芥种子进行30 keV 40Ar离子辐照后，包括萌发、根毛分化、初生根伸长、侧根起始和存活在内的短期和长期胚后发育均受到显著抑制。由于茎尖分生组织和根尖分生组织细胞没有直接受到辐射损伤，结果表明损伤信号从受辐照细胞传递到茎尖分生组织和根尖分生组织细胞，并导致最终的发育改变，这表明完整种子中存在长距离旁观者/远隔效应。对机制的进一步研究表明，这些效应与胚后发育中活性氧（ROS）生成的增加或生长素依赖性转录的减少有关。用ROS清除剂二甲基亚砜（DMSO）或合成生长素2,4-二氯苯氧乙酸（2,4-D）处理可以显著逆转胚后发育和生长素依赖性转录的改变，表明ROS和生长素依赖性转录过程在完整生物体中低能重离子辐射诱导的长距离旁观者/远隔效应中起重要作用。
